[Solved] Which neurotransmitter system do psychedelics primarily act on?

Psychedelics primarily act on the serotonin system, particularly via the 5-HT₂A receptor. This receptor is a subtype of the serotonin (5-hydroxytryptamine, or 5-HT) receptors and plays a central role in the development of the psychedelic experience, such as:

1. Visual hallucinations

2. Changed perception of time

3. Ego dissolution

4. Emotional intensification

Key features of this mechanism:

1. Agonism at 5-HT₂A receptors (as with LSD, psilocybin, DMT) leads to increased activity in certain brain areas, but also to desynchronization of networks such as the Default Mode Network (DMN).

2. This causes an “expanded consciousness” because normal patterns of self-perception and perception are let go.

3. Other serotonin receptors such as 5-HT₁A, 5-HT₂C can also contribute to mood and cognitive modulation.

Exceptions:

1. Ketamine works primarily on the glutamate system via blockade of NMDA receptors.

2. MDMA works primarily through release of serotonin, dopamine and noradrenaline, and influences the system indirect.

In short: classic psychedelics (LSD, psilocybin, DMT) work directly as agonists on the serotonergic system, with an emphasis on 5-HT₂A receptors, which explains their unique psychological and therapeutic effects.

In this overview, we describe for each substance the neurobiological action (receptor profiles and involved neurotransmitters), the physical effects, the mental and perceptual effects, and current insights into therapeutic applications.

DMT (N,N-dimethyltryptamine)

Neurobiological function

DMT is a psychedelic tryptamine that acts primarily as an agonist on serotonin (5-HT) receptors. It binds particularly to the 5-HT_2A receptor – the key receptor associated with hallucinogenic effects – but also to 5-HT_1A and 5-HT_2C receptors. This receptor activation leads to a strong disruption of sensory and cognitive networks. Additionally, there are indications that DMT has other targets: for instance, in high concentrations, it can activate the sigma-1 receptor, which may contribute to modulating effects on glutamate and dopamine pathways, among others. DMT shares a structural similarity with the body's own neurotransmitter serotonin and acts as a so-called serotonergic hallucinogen.

Physical effects

Under the influence of DMT, distinct physiological reactions occur. Clinical research (with intravenous administration) has shown that DMT affects blood pressure and heart rate. slightly increases, the pupils dilate and body temperature rises slightly. Hormonal stress responses are also observed: for instance, concentrations of cortisol, prolactin, and other stress hormones rise briefly after DMT intake. In higher doses, DMT causes significant activation of the cardiovascular system (increased systolic/diastolic blood pressure) – usually temporary in nature. Although DMT is generally safe in terms of physical toxicity, acute side effects such as an accelerated heart rate, increased blood pressure, or other cardiovascular effects occur, especially in people with a predisposition for them.

Mental and perceptual effects

DMT is notorious for its intense psychedelic experience. Within seconds after inhalation or injection, it induces vivid visual hallucinations – often complex, colorful geometric patterns and even the sensation of perceiving entities or beings. Users report drastically altered sensory perception, a distorted sense of time, and phenomena such as ego dissolution (loss of the sense of a defined self). Also characteristic are out-of-body experiences and the feeling of being “in another reality”. Emotionally, DMT can go in any direction: from ecstatic insights to overwhelming fear or paranoia during a “bad trip”. During the peak, there is often a detachment from ordinary reality (depersonalization/derealization) and a state of consciousness that is difficult to describe. Nevertheless, users generally realize that the visual spectacle is caused by the drug (so-called pseudohallucinations that are not confused with reality). Tolerance to repeated doses sets in quickly afterwards (what is unique is that DMT no builds up long-term tolerance like LSD does).

Therapeutic insights and applications

DMT is traditionally used ritually (e.g., in ayahuasca brews) and there is growing scientific interest in its potential therapeutic value. Current insights suggest that DMT can induce powerful transpersonal experiences that, provided in the right setting, can be psychologically healing. Clinical trials are underway into DMT-assisted therapy for depression – due to its short duration of action, DMT is seen as a “scalable” alternative to longer-acting psychedelics in clinical use. DMT (in the form of ayahuasca) showed positive effects in preliminary studies for the treatment of addiction and depression, presumably by promoting introspection and neuroplasticity. For example, short-acting DMT is being investigated for treatment-resistant depression. Although results are promising, DMT is not yet recognized as a medicine outside of research settings. Furthermore, the intense psychological effects are challenging – professional guidance is essential to address any potential emotional breakthroughs to manage properly.

Psilocybin (psilocin)

Neurobiological function

Psilocybin (from mushrooms) is converted in the body into psilocin, the actual active compound. Psilocin is a tryptamine that is very similar to DMT and acts as an agonist on multiple serotonin receptors, with emphasis on the 5-HT_2A receptor. Activation of 5-HT_2A in the cerebral cortex triggers complex signaling cascades (via G_q/11 and β-arrestin pathways) that cause the psychedelic state. Although 5-HT_2A plays the leading role in hallucinogenic effects, psilocin also binds to other serotonin receptors: it even has high affinity for 5-HT_2C, 5-HT_1A and 5-HT_2B. These additional receptor interactions likely do not contribute to the hallucinations, but could play a role in the modulation of mood and therapeutic effect. Psilocin has little direct influence on other neurotransmitter systems: it acts hardly binds to dopamine or noradrenaline receptors. For instance, it has a negligible affinity for the serotonin transporter (SERT) and no direct action on the dopamine (DAT) or norepinephrine transporter (NET). It also barely affects dopamine D2 receptors and does not bind significantly to adrenergic, muscarinic, histamine, or opioid receptors. In summary: psilocin acts selectively serotonergically, with the 5-HT_2A receptor as the primary target, which explains the typical mind-altering effects.

Physical effects

Psilocybin causes mild to moderate physical effects, largely resulting from central sympathetic activation. Common acute physiological reactions are pupil dilation and changes in heart rate and blood pressure. In studies, a slightly increased heart rate was observed in ~56% of the users (sometimes actually a decrease in a few), and blood pressure changes varied from slight hypertension to hypotension. In general, these cardiovascular effects are mild: on average, heart rate increases by only ~5 beats/min and systolic blood pressure by 10–15 mmHg. However, a temporary blood pressure spike can pose risks in vulnerable individuals (especially in those with pre-existing hypertension). Other frequently reported physical side effects are nausea – in ~44% in one study – which is often associated with eating the mushrooms themselves. In addition, increased muscle tension and tremors for (in ~25% of users) as well as yawning and fatigue. Sensory reflexes may become heightened (increased muscle speech reflex). In short, psilocybin is physical relatively mild sympathomimetic: slight increase in heart rate/blood pressure, dilated pupils, slight loss of coordination (dysmetria), and sometimes stomach complaints. These effects usually disappear within a few hours without residual damage.

Mental and perceptual effects

Psilocybin is known for profound changes in perception, cognition, and mood. Visual hallucinations are typical: with closed eyes, users see vivid, colorful geometric patterns, and with open eyes, distortions of objects or a wave motion in surfaces. Colors are often perceived more intensely, and synesthesia phenomena may occur (for example, “feeling” colors or “seeing” sounds). perception of time becomes severely distorted – minutes can feel like hours, and one has the feeling of being in a timeless state. Emotionally reinforced Psilocybin emotional intensity: euphoria, wonder, and a sense of connection with the world are common. At the same time, the capacity for introspection is heightened, and long-repressed memories or emotions can surface vividly (often with a strong emotional charge). In high doses, this often occurs. ego loss (ego dissolution) on: the user temporarily loses the sense of a separate self and experiences oneness with the environment or the universe. Negative psychological reactions are also possible, particularly in an unsafe environment. set and setting: anxiety, paranoia or panic attacks can be part of a “bad trip”. Also depersonalization or derealization It has been reported – the feeling of being detached from reality – usually temporary during the trip. In general, the effects of psilocybin closely resemble those of LSD, although psilocybin is often described as “warmer” and more emotionally connecting than LSD. Hallucinations under psilocybin are usually not mistaken for reality.; Users retain some awareness that the experienced visions are drug-induced (which is why they are sometimes referred to as pseudohallucinations). After the trip, an aftermath of hours to a day may follow, involving fatigue or mood swings, but structural, long-lasting psychoses or HPPD (persistent perceptual disturbances) are rare.

Therapeutic insights and applications

Psilocybin has emerged in recent years as a promising therapeutic tool, particularly in psychiatry. Current insights demonstrate that a single psilocybin session (in combination with psychotherapy) can provide profound and long-lasting improvement for certain conditions. For example, clinical studies have shown that psilocybin therapy fast can bring about a reduction in depressive symptoms in patients with treatment-resistant depression. In Australia, psilocybin was even approved in 2023 for the treatment of therapy-resistant depression under strict medical supervision. In the US and Europe, psilocybin is also in the final phase of clinical trials for depression. In addition to depression, psilocybin is being investigated for anxiety in terminal cancer patients, post-traumatic stress disorder (PTSD), addiction problems (such as alcohol addiction) and obsessive-compulsive disorder. In this context, patients often reported mystical or emotional breakthrough experiences which were associated with therapeutic advances. The mechanisms of action are still being investigated, but psilocybin appears to “reset” brain networks via 5-HT_2A agonism and promote neuroplasticity – which may be the long-lasting antidepressant effects explains after only one or two doses. Beyond psychiatry, there are small studies suggesting that psilocybin (and related tryptamines) can interrupt or long-term reduce cluster headache attacks, an effect also seen with LSD. In summary, psilocybin is now known as a potentially revolutionary treatment: in scientific reviews, it is cited as one of the most promising new therapies for certain major depressive disorders. It is important, however, that these applications take place under strictly controlled clinical conditions, given the potential of psilocybin to provoke strong psychic reactions. Nevertheless, it holds true that where conventional treatments fail, psilocybin-assisted therapy has been successful in a subset of patients. rapid and long-lasting improvement brought. This has led to renewed acceptance – for instance, therapists in some regions (e.g. Oregon, USA) are already receiving training in psilocybin therapy. Further large-scale studies still need to confirm the safety and optimal protocols, but preliminary results position psilocybin as a groundbreaking therapeutic tool in psychiatry.

LSD (lysergic acid diethylamide)

Neurobiological function

LSD is a semisynthetic hallucinogenic substance from the lysergamide family and has a very broad receptor profile. The most important point of leverage is the 5-HT2A serotonin receptor, to which LSD binds with high affinity as a (partial) agonist. This triggers, just like with psilocybin, changes in signaling pathways responsible for the psychedelic effects. However, LSD's pharmacology is more complex: the molecule binds to multiple serotonin subtypes (5-HT_1A, 5-HT_1B, 5-HT_2C, 5-HT_5A, 5-HT_6, 5-HT_7). Additionally, LSD affects dopamine receptors – particularly D_2 and D_1 – and on certain adrenergic receptors. In a neuroimaging study, it has been confirmed that LSD 5-HT_2A, 5-HT_2C, 5-HT_1A/B, 5-HT_6, 5-HT_7 receptors stimulates and also measurably binds to dopamine D-1/D-2 receptors in the cerebral cortex. This pleiotropic receptor affinity explains why LSD's effects strongly correspond to classic serotonergic hallucinogens on the one hand, but have additional stimulant properties and a longer duration on the other. The influence on dopamine, for example, may contribute to the mild euphoria and increased energy that LSD sometimes provides, while 5-HT_1A agonism in the raphe nuclei, among others, causes perceptual gating. LSD's interaction with 5-HT_2B (serotonin-2B on heart valves) is known in vitro, but plays no significant role in occasional use (the risk of heart valve fibrosis arises primarily with chronic 5-HT_2B agonism, which is rarely the case with LSD use). In summary: LSD mimics serotonin on countless receptors, of 5-HT_2A as primary target, and has additional dopaminergic and adrenergic effects. This broad receptor profile leads to the characteristic mixture of strong sensory disturbance and subtle stimulation that LSD brings about.

Physical effects

LSD causes physical effects that are typical of a mild sympathomimetic stimulant. Users often experience dilation of the pupils, a slight increase in the heart rate and blood pressure, and a slightly elevated body temperature. Clinical studies show that LSD (100–200 µg oral doses) moderately increases blood pressure (systolic and diastolic on average 10–15 mmHg above basal) and significantly accelerates the heart rate. In a direct comparative study, LSD was found to increase heart rate more strongly than an equivalent dose of psilocybin. Typical physical side effects during the LSD trip are dry mouth, light tremor or muscle twitching, and sometimes nausea. Also sweating and chills can occur due to the disruption of body temperature. Many people suffer from muscle tension, especially in the jaw (jaw clenching) or neck. Nevertheless, these symptoms are experienced as mild by most users – LSD, for example, increases blood pressure and temperature but mediocre compared to physical stress. Objectively, during LSD intoxication, are often dilated pupils and a raised reflex reactivity to be seen. LSD also has some unique anesthetic properties: unlike classic sedatives, LSD does not suppress breathing and the user retains muscle control (up to high doses where disorientation occurs). However, in high doses or in case of hypersensitivity, LSD can trigger unpleasant somatic reactions such as dizziness, confusion or fainting. Acutely dangerous side effects are rare; LSD is not directly cardiotoxic and dose levels for physical toxicity are extremely high. Nevertheless, a few medical emergencies have been reported due to indirect effects – for example hyperthermia during prolonged physical exertion on LSD or accidents due to loss of coordination. In general, the physical strain on LSD is low: mild fight-or-flight features (tachycardia, hypertension, mydriasis) and some sensory disturbances (blurred vision, tingling).

Mental and perceptual effects

LSD is notorious for the powerful changes in consciousness who causes it. The psychological effects typically begin 30–60 minutes after ingestion and last 8–12 hours. Visually, LSD causes vivid hallucinations and distortions: colors appear more intense, objects may wave or breathe, and complex fractal patterns appear when one closes the eyes. Open-eyed hallucinations under LSD are often very detailed but are usually not perceived as real – the user often realizes that what he sees is caused by the drug. Auditory changes can also occur (for example, music becomes extremely immersive or one hears echoes). LSD merges senses Sometimes (synesthesia): one can “see” sounds or “hear” colors in a phenomenon of sensory cross-connections. Cognitively, LSD causes accelerated, associative trains of thought; thoughts can get caught in loops and normal logic fades. Users often report profound insights or philosophical reflections, but confusion is also not uncommon. Emotionally, LSD has an amplifying effect: positive feelings such as euphoria, wonder and mystical ecstasy can manifest, but likewise latent fears or insecurities can be magnified. In high doses is ego dissolution possible: one temporarily loses the boundaries of one's own ego, which can be experienced as a sense of spiritual unity but can also be frightening. Negative effects with LSD are usually related to set/setting or dosage: paranoia, delusions and intense fear can characterize a “bad trip.” LSD can also bring latent psychoses to the surface in vulnerable individuals. During an LSD trip, reality orientation is significantly impaired – although one generally retains some basic awareness, behavior can become dangerously impulsive if fear or delusions take over. After the acute effects, aftershocks may occur such as flashbacks: spontaneous, brief reliving of hallucinations days or weeks later (LSD users ~5% reports this). Also HPPD (Hallucinogen Persisting Perception Disorder), persistent visual disturbances, is a rare complication among very frequent users. In summary, LSD produces a multifaceted spectrum of mental effects: from expanded perception and creative insights to potentially disorienting thought patterns and emotional extremes. The intensity and duration of LSD's effects make it one of the most powerful psychedelics, which explains both its unique therapeutic potential and the risks.

Therapeutic insights and applications

LSD was already being investigated in the 1950s and 1960s as an aid in psychotherapy (for example, for alcoholism and anxiety in terminally ill patients). These early studies sometimes showed remarkable improvements – a 2012 meta-analysis found that one LSD session, combined with psychosocial treatment, could provide reduced alcohol cravings for months. However, methodological flaws in older trials made the results difficult to interpret at the time. In recent years, LSD research has cautiously revived. Anxiolytic effectsSmall-scale modern studies suggest that LSD-guided therapy can reduce existential anxiety in, for example, cancer patients. Addiction: LSD shows a reduction in addictive behavior in some cases (historically studied primarily in alcohol addiction). Most striking is current research into LSD in anxiety disorders: in 2024, the FDA granted the breakthrough therapy-status to an LSD preparation (MM-120) for the treatment of generalized anxiety disorder. This means that preliminary clinical results were promising enough to justify accelerated follow-up research. Indeed, a recent study showed that a single LSD dose (100 µg) in a therapeutic setting resulted in significant anxiety reduction in patients with anxiety disorder. In addition, LSD has been investigated for cluster headache and pain management: small patient series report that low LSD doses can prevent or alleviate cluster headache attacks. Mechanistically, it is hypothesized that LSD—via 5-HT2A agonism and promotion of neuroplasticity—can break rigid thought and behavior patterns, which may be valuable in treatment-resistant psychiatric disorders. LSD is also sometimes used in microdosing (approx. 5–20 µg) in the hope of achieving subtle cognitive or mood benefits, but scientific evidence for this is currently limited and mixed. Despite renewed research interest, LSD remains illegal for use in virtually all countries; treatments take place only within a research setting. Nevertheless, some experts consider LSD to be a potential “psychoplastogenic” – a substance that rapidly increases neural plasticity – and is therefore potentially useful for hard-to-treat depression or anxiety. In summary: LSD's therapeutic application is (once again) in its infancy, but Initial results are encouraging for, among others, anxiety disorders and addiction. It is important that LSD therapy is always combined with intensive psychological counseling to manage the experience. In the coming years, larger-scale trials (partly funded by non-profit organizations) will provide more clarity regarding the safety and effectiveness of LSD in the clinic.

Ketamine

Neurobiological function

Ketamine is a dissociative anesthetic with a completely different mechanism of action than classic serotonergic psychedelics. It acts primarily on the glutamate system as non-competitive antagonist of the NMDA receptor (a subtype of glutamate receptor). Ketamine blocks NMDA receptor channels on excitatory neurons, particularly on GABA interneurons in the cortex. As a result, it reduces normal GABA inhibition and inhibits the glutamate tracts. The net effect is a increase in glutamate release particularly in the prefrontal cortex. This glutamate pulse activates AMPA receptors on postsynaptic neurons, which sets an entire cascade in motion: increased release of Brain-Derived Neurotrophic Factor (BDNF) and activation of the mTOR pathway, leading to synaptic growth and enhanced neuroplasticity. This neurobiological change is seen as an explanation for ketamine's unique rapid antidepressant effect: within hours after ketamine infusion, new connections between brain cells can form that break depressive patterns. In addition to NMDA blockade, ketamine has weaker secondary targets. For example, the molecule binds at low affinity to mu- and kappa-opioid receptors, but this effect is much weaker than NMDA inhibition. Nevertheless, research indicates that ketamine's antidepressant effect is partly dependent is of a functioning opioid system – administration of an opioid antagonist (naltrexone) can weaken the mood improvement. This suggests that ketamine indirectly endorphin/opioid release stimulates, without itself being a classical opioid agonist. Furthermore, ketamine increases dopamine levels in reward areas (including the striatum) – not through dopamine reuptake inhibition, but indirectly via NMDA antagonism that disinhibits dopamine cells. The discussion on whether ketamine is directly a D-2-dopamine agonist is, remains undecided; some in vitro data suggested weak D-2 partial agonism, but in vivo this is likely negligible at typical dosages. Finally, ketamine also affects nicotinic acetylcholine receptors and sigma receptors to a slight degree, but again at concentrations higher than those used clinically. All things considered, NMDA receptor blockade the core mechanism: this results in an acute glutamate overlux followed by a synaptic “reset” in brain networks involved in cognition and mood. This neuropharmacological profile makes ketamine unique: it is not a classic “psychedelic” but a dissociative anesthetic that, even at sub-anesthetic doses, causes powerful changes in consciousness and rapid causes neuroplasticity.

Physical effects

Ketamine's physical effects differ from serotonergic substances and resemble those of a anesthetic mixed with stimulant. A striking characteristic is that ketamine the sympathetic nervous system activates: heart rate and blood pressure increase after administration significantly more than with other anesthetics. Ketamine causes a dose-dependent increase in blood pressure (systolic and diastolic), heart rate, and cardiac output; peak values are usually reached within a few minutes immediately after injection. This is because ketamine causes the release of endogenous catecholamines (adrenaline/noradrenaline) – an indirect sympathomimetic effect. For instance, it has been reported that blood pressure increases of 10–50 TBP above baseline occur shortly after induction. In healthy individuals, these cardiovascular parameters usually normalize spontaneously within ~15 minutes. Due to this property, ketamine is valued in anesthesia for hypovolemic patients (it prevents hypotension). However, in people with heart problems, the hypertensive response can be risky; ketamine is then contraindicated or requires close monitoring. In addition to the heart and blood vessels, ketamine also affects other systems: for instance, it can slightly accelerate breathing, but the remarkable thing is that ketamine itself rarely causes respiratory depression in higher doses. Eye movement disorders (nystagmus) and wide open pupils occur during intoxication. Dizziness and loss of balance are common – ketamine disrupts cerebellar coordination, leading to unsteady walking or difficulty with fine motor skills. Nausea and vomiting can occur when ketamine wears off (just like with many anesthetics). Also muscle weakness or muscle stiffness has been reported. The phenomenon of is unique. analgesia: ketamine strongly dulls the sensation of pain (hence its use as a painkiller). Users often feel sedated or “light in the body”. At higher recreational doses, the so-called “K-hole” on: physically, the person appears motionless or very sluggish, with reduced response to stimuli (anesthesia-like). This is often accompanied by dissociation and vivid hallucinations, while the muscles may be relaxed or, conversely, mildly spastic. Other frequently reported acute side effects are numb limbs, speech problems (poor articulation, as if the mouth is “numb”) and sometimes involuntary muscle movements. Ketamine also slightly stimulates the secretion of saliva and mucus, causing patients sometimes extra salivation or experience pressure on the airway – therefore, atropine is sometimes administered for medical applications. Summary: ketamine increases acute the cardiovascular activity (tachycardia, hypertension) causes a dissociative immobility at higher doses, and leads to analgesia and mildly impaired motor skills. These effects appear rapidly (within minutes) and are relatively short-lived; for example, blood pressure and heart rate return to normal within ~15–30 minutes post-dose. Because ketamine alters consciousness without deep respiratory depression, it has an important safety profile in medical emergencies. For recreational users, however, this means that physical accidents can occur (due to impaired coordination) while vital functions remain intact, which sometimes gives a false sense of “safety.” Combining ketamine with other substances can be dangerous: with sedatives, respiratory arrest is a risk, and with stimulants, extreme hypertension can occur.

Mental and perceptual effects

Ketamines psychological effects distinguish themselves strongly from classic hallucinogens and are characterized as dissociative. This means that ketamine a feeling of separation between mind and body causes. Altered perception is reported even at low doses: mild distorted sensory input, a dreamy and slowed pace of thought, and depersonalization (the feeling as if one is observing oneself from the outside). A peculiar mixture of sedation and stimulation occurs: thoughts may drift away or fragment on the one hand (as if one is half asleep), while on the other, a chaotic internal stream of images or ideas may arise. Perceptual can ketamine mild hallucinations produce, particularly with closed eyes: users often describe kaleidoscopic or “ghost-eye” images, and experiential worlds that are detached from the physical environment. With open eyes, one is more likely to see distortions and a haze/blur, rather than the sharp hallucinations associated with LSD. The sense of space and time becomes severely distorted – minutes and meters no longer make sense. Characteristic of ketamine is the “out-of-body experience”: one feels literally disconnected from the body, sometimes floating above oneself or in another dimension. In this state – at higher doses the K-hole – one can become completely absorbed in internal hallucinatory scenarios, ranging from abstract and cosmic to nightmarish. People have provided descriptions in K-holes of near-death experiences, encounters with entities, or entering strange “ketamine worlds”. Emotional Ketamine is ambivalent: some users experience euphoria and calm bliss, while others experience anxiety and panic, depending on mindset and environment. Often there is a flatness or detachment from emotion – one observes feelings from a distance. Ketamine can also psychotic-like symptoms trigger (delusions, paranoia) during a high-dose episode, but these usually disappear as soon as the substance wears off. Cognitively, ketamine causes clear reduction of sharpness and memory During intoxication: short-term memory falters, speech becomes incoherent, and simple thought patterns require effort. This contributes to dissociation; one is, as it were, “numbed” in thought. In a controlled setting, this cognitive disinhibition can be utilized therapeutically – for example, patients dare to speak about trauma more easily because the usual emotional response is dampened. In the aftermath (hours later), users often feel hazy, sometimes emotionally unstable, or conversely euphoric. In summary does ketamine give a unique state of consciousness: a dreamlike dissociation in which the sense of reality diminishes, pain and fear often disappear, and intense inner experiences (visual and existential) can occur. All this without the classic structure or “insights” of serotonergic trips – ketamine experiences are rather fragmented, mysterious, and sometimes frightening due to their elusiveness.

Therapeutic insights and applications

Ketamine is special because it already has a recognized medical application and recently represented a breakthrough in psychiatry. Anesthesia and pain managementKetamine has been safely used as an anesthetic for decades, particularly for short procedures or in emergency situations. The preservation of spontaneous breathing and blood pressure makes it ideal for surgical patients at risk of shock; it is therefore included on the WHO list of essential medicines. Additionally, ketamine is used as a powerful analgesic (painkiller) for major traumas, among other things, or as an adjunct to general anesthesia to minimize the use of opioids. Psychiatry – depressionThe greatest recent development is the use of ketamine in treatment-resistant depression. Low, subanesthetic doses (typically 0.5 mg/kg IV infusion over 40 min) proved to be lightning-fast antidepressant response to be administered within 1 day in patients where conventional antidepressants failed. Studies reported response rates >60% within 4–24 hours after a single infusion (compared to ~20–40% with placebo), and although this effect diminishes after a week, a longer-lasting improvement can be achieved with repeated dosing. This discovery – first published in 2006 – is regarded as ""the most important breakthrough in depression treatment in 50 years"It has led to the development and approval of esketamine (the S-enantiomer of ketamine) nasal spray as a registered medicinal product. In 2019, the FDA and EMA approved esketamine for treatment-resistant depression, as an adjunct alongside antidepressants. This drug (Spravato) is now used clinically, albeit under strict conditions (administration only in a clinic, by a physician, due to possible side effects). Racemic ketamine itself is administered intravenously off-label in specialized centers to depressed patients, often with impressive results when nothing else works. Mechanism of action in depressionThe hypothesis is that ketamine, via NMDA blockade and the subsequent glutamate boost, “pulls” the brain out of rigid, depressed network connectivity and stimulates synaptic renewal. This is supported by animal research showing that ketamine increases the number of spinous processes (synaptic connections) in the prefrontal cortex within hours and restores stress-related synapse loss. PTSD and other conditionsIn addition to depression, ketamine is being investigated for post-traumatic stress disorder, anxiety disorders, and bipolar depression. Results for PTSD are mixed but promising; some small RCTs show rapid reduction in anxiety and re-experiencing. Ketamine also appears to be effective for chronic pain syndromes (e.g., CRPS) and is occasionally used to break opioid tolerance or counteract opioid-induced hyperalgesia. Ketamine-assisted psychotherapy: A new area is the combination of ketamine with psychotherapy for, for example, addiction or existential distress. This utilizes ketamine's ability to disconnect and its neuroplasticity to allow patients to step outside their fixed mental frameworks, after which therapeutic insights are better retained. The term ""psycholytic therapy"" has indeed been used for this. Clinical research is underway for, among others, alcohol addiction and cocaine addiction, with some promising results (ketamine sessions led to longer abstinence compared to placebo). RegulationsKetamine is recognized as a medicine worldwide, but recreational use is punishable by law. Because the dose-response for antidepressants is lower than for anesthesia, administration is relatively safe provided it is monitored. However, there is a need for more data on the long-term consequences of repeated ketamine use for depression – including on cognitive functioning and bladder health (high-dose ketamine abuse can cause severe bladder damage). For the time being, protocols are generally limited to a few infusions spread over weeks. Conclusion: Ketamine has proven itself on the one hand as safe anesthetic, on the other hand, it marks the rise of “rapid acting antidepressants”. It offers hope for patients for whom standard medication fails, although caution remains necessary due to its addiction and abuse potential. Ketamine forms a unique link between the world of anesthesia, psychedelics, and psychotherapy, and it is seen by many as an example of how neuroplasticity-inducing substances can innovate psychiatry.

MDMA (3,4-methylenedioxymethamphetamine)

Neurobiological function

MDMA, better known as “ecstasy”, is not a classic hallucinogen but a entactogen/amphetamine derivative with a unique mechanism of action. Unlike LSD or psilocybin (which act directly on receptors), MDMA works primarily indirectly via neurotransmitter release. It massively stimulates the release of serotonin from nerve cells, and to a lesser extent from dopamine and noradrenaline. MDMA binds to the serotonin transporter (SERT) at presynaptic terminals and reverses the transporter function, causing serotonin to be pumped out of the neuron into the synaptic cleft instead of being reuptaked. A single MDMA dose can thus lead to an increase in extracellular serotonin by a factor of 10 or more in certain brain regions. In addition, MDMA also inhibits the reuptake of dopamine (via DAT) and noradrenaline (NET), causing these neurotransmitters to accumulate outside the cells as well. The The serotonergic effect is, however, the strongest. – MDMA is classified as potent serotonin releaser. The enormous serotonin surpluses subsequently activate various 5-HT receptors: 5-HT_1A (determined for mood enhancement and anxiety suppression) and 5-HT_2A (possibly involved in mild hallucinogenic aspects such as light enhancement), among others, play a role. Interestingly, MDMA also affects the release of oxytocin induces via serotonin 5-HT-1A stimulation in the hypothalamus. Oxytocin – the “cuddle hormone” – is associated with MDMA’s characteristic empathogenic effects (feelings of connectedness and trust). The dopaminergic effect of MDMA contributes primarily to the stimulation and euphoriaIncreased dopamine in the reward circuit provides energy and pleasant excitement. Noradrenaline release ensures alertness and sympathetic activation (increase in heart rate/blood pressure). In short, MDMA functions as monoamine releaser in the central nervous system: it “floods” the synapses with serotonin (primary), dopamine, and noradrenaline. This unique combination explains the entactogenic profile: on the one hand stimulation and excitement (by DA/NA), on the other hand warm empathic affect and mood swings (by 5-HT/oxytocin). MDMA does not have a pronounced direct agonistic effect on classical post-synaptic receptors as psychedelics do, but secondary receptor activation by neurotransmitters is widespread. Because MDMA is an amphetamine analogue, it belongs to the substituted amphetamines in chemical classification. At high doses, it causes neurotoxic stress on serotonin axons, presumably due to the combination of excessive serotonin release and the formation of oxidative metabolites. This is relevant in cases of repeated abuse, but less so in cases of occasional therapeutic administration.

Physical effects

MDMA causes clear physiological stimulation through activation of the sympathetic nervous system (similar to amphetamines). The user notices the physical effects almost immediately. an increased heart rate and blood pressure. The dilate pupils strong (mydriasis) and often remain large throughout the entire duration of action. Due to the combination of activity and environment (often dancing in warm rooms), the body temperature rise; MDMA itself contributes to this by disrupting thermoregulation in the hypothalamus. Overheating (hyperthermia) is a serious risk at high doses or during prolonged physical exertion under MDMA, and is responsible for a portion of MDMA deaths (in combination with dehydration). MDMA also causes sweating and sometimes chills due to alternating vasodilation/constriction. A well-known characteristic is tensing jaw muscles and grinding teeth (bruxism): users unconsciously clench their jaws, leading to teeth grinding – this is so typical that chewing gum is often carried along to compensate for the effect. Other short-term side effects are dry mouth, blurred vision (because the focusing of the eyes decreases), and muscle tension in the neck and limbs. Some people experience nausea or a slightly agitated feeling in the stomach upon arrival, similar to “butterflies in the stomach”. Tremor or mild spasms may occur due to the stimulation. In general, users feel physically energetic and irritable – MDMA slightly suppresses feelings of fatigue and pain signals, which contributes to being able to dance for hours. At the same time, MDMA can promote urine retention (via ADH release), whereby water intoxication poses a risk if one drinks excessively out of fear of dehydration. For instance, there are a few known cases of hyponatremia due to massive water intake after MDMA. In summary are the acute physical MDMA effects: accelerated heart rate, increased blood pressure, hyperthermia, sweating, pupil dilation and bruxism, plus often euphoric energy and reduced fatigue. Most of these effects peak around 1–2 hours after ingestion and level off in ~4–6 hours. Upon wearing off, one often feels physical exhaustion, partly due to serotonin depletion and sleep deprivation. MDMA is notorious for a ‘Tuesday slump’ or hangover: a few days after use, fatigue, muscle pain, and general lethargy may occur as a rebound effect of the physical exertion.

Mental and perceptual effects

MDMA's popularity stems from the unique mental effects which it brings about: it is characterized as empathogenic or entactogen, which refers to the evocation of empathy and inner connection. Within approximately 30–60 minutes after ingestion, users feel a strong mood improvement and euphoria – an all-encompassing sense of well-being and loving happiness. Fear and inhibitions fall away; instead, there arises empathy and connection with othersUsers describe feeling intense love or understanding for both friends and strangers, and a deep need to express these feelings (hugging, having personal conversations). This pro-social effect distinguishes MDMA from classic stimulants. At the same time, MDMA provides a energetic alertness and increased sociability: one is talkative, extroverted, and feels confident in social situations. Sensory-wise, MDMA has a mild reinforcing effects: music sounds fuller and more immersive, colors can appear brighter, and touch feels more intense or pleasant. Real hallucinations or strong changes in sensory perception such as with LSD usually do not occur with MDMA – at most slight visual distortions (at high doses some light flickering, “trails” behind moving objects, or closed-eye vision). Mental clarity is relatively preserved at first, although one often notices a increased opennessThoughts about personal issues come more easily and without negative charge. MDMA promotes introspection. without overwhelming fear, causing emotional breakthroughs be possible in a therapeutic context (patients can, for example, discuss traumatic memories with a reduced anxiety response). This is precisely why MDMA achieves such good results in PTSD psychotherapy: the substance creates a “safe emotional window” in which difficult feelings can be processed. Cognitive Under MDMA, there is a mild stimulation – thinking is fluid but primarily focused on positive or empathetic subjects. Making complex calculations or rational reasoning is not central; rather, one feels a deep insight in emotional or relational matters, however often without sober objectivity. Negative mental effects can be from MDMA: restlessness, distraction (less concentration), sometimes confusion when stimuli become too much. Occasionally, the euphoria turns into anxiety or panic, particularly in the event of an overdose or in a crowded environment – one may then feel overwhelmed by palpitations and intense sensations. Paranoia or hallucinations are very rare, but can occur if the serotonin supply becomes depleted (for example, in the morning after using all night, sometimes mild delusions or sensory noise). In the days following, a dysphoric aftermath notorious: users report depressive feelings, irritation, or emptiness (“Suicide Tuesday”), because serotonin is temporarily depleted and the reward system needs to recover. With moderate use, these after-effects are limited to fatigue and melancholy for 1–2 days. In summary does MDMA give a unique psycho-emotional profile: intense positive mood, empathy and connectedness, sensory appreciation (especially music), increased energy and talkativeness, and suppression of negative emotions. This is accompanied by reduced anxiety and increased emotional openness, creating a sense of “emotional healing” can provide. It is precisely these properties that make MDMA interesting as a therapeutic tool: it can help people look at themselves and their trauma with compassion.

Therapeutic insights and applications

MDMA was originally developed (in the 1970s) as a possible adjunct to psychotherapy and currently has the status of potential breakthrough therapy, especially for PTSD (post-traumatic stress disorder). Current statusMultiple phase II and phase III studies have shown that MDMA-assisted psychotherapy can be remarkably effective for chronic, treatment-resistant PTSD. In these guided sessions (typically 2–3 MDMA sessions supervised by therapists), researchers observed drastic decreases in PTSD symptom scores, with a significant proportion of patients no longer meeting PTSD criteria after treatment. These results led the US FDA to grant MDMA the status of a drug in 2017. “Breakthrough Therapy” provided for PTSD treatment, to accelerate further development. It is expected (as of 2025) that MDMA will be used in the US within the foreseeable future regularly approved are being used as part of psychotherapy for PTSD, given the positive outcomes of phase III research. Australia led the way in this: as of July 2023, MDMA is permitted there – under very strict conditions – in psychiatry for PTSD treatment, limited to qualified doctors/psychiatrists. The therapeutic model relies on MDMA's unique mechanism of action: it reduces anxiety and defensiveness, increases trust in the therapist, and stimulates processing, allowing patients to relive traumatic experiences and work through them emotionally without being overwhelmed by fear. Beyond PTSD, MDMA is also being investigated for other conditions where social anxiety or emotional rigidity play a role. For example, in autism spectrum disorder (social anxiety in autistic adults) a small study showed improved social function after MDMA sessions. Also for therapy for addiction (such as alcoholism) pilot studies exist: the idea is that MDMA, under supervision, can help process underlying traumas or emotions that fuel addiction, thereby reducing the craving for the substance. Furthermore, research into MDMA is ongoing for eating disorders and life stage therapy in palliative cancer care (reducing fear of death). It is important to emphasize that MDMA is always studied in combination with psychotherapy, not as a stand-alone medication. Medical admissionAt present (2025), MDMA is not yet a generally registered medicine, except within the framework of research or compassionate use programs. In the Netherlands and most other countries, recreational use is illegal, but scientific trials are ongoing or have been completed. It is expected that within 1–2 years (possibly 2024 or 2025), MDMA will be officially approved in the US for PTSD treatment, followed by Europe once the EMA reviews the data. This would be a first: MDMA would then become the first in its class (entactogens) with a medical indication. Safety in a therapy settingStudies report that MDMA therapy under medical supervision is generally safe; no serious cardiovascular events occurred, nor were there any signs of addiction within the protocols. However, the sessions are medically monitored (heart rate, temperature) to detect hyperthermia or hypertensive reactions in a timely manner. Psychologically, a short-term increase in anxiety or sadness was sometimes observed during the integration of traumatic memories, but this is part of the therapeutic process and was managed with support. A point of attention is the neurotoxicity with repeated frequent useRecreational abuse of MDMA can cause permanent serotonin depletion and memory problems, but at limited therapeutic doses (and long intervals), this risk appears minimal. ConclusionMDMA is rapidly shifting from a banned party drug into a potentially valuable medicine in psychotherapy. It uniquely combines anxiolytic and empathogenic effects, temporarily placing patients in a mental state optimal for trauma processing and emotional healing. If the current trend continues, MDMA-assisted therapy could become an accepted treatment method for PTSD (and perhaps other stress-related disorders) within a few years, naturally within strict medical frameworks. In this way, MDMA illustrates that substances that were once used only as “"drug"” were seen, can be powerful therapeutic instruments in the right context.

Sources:

Frontiers | Nature