[Solved] How does LSD work?

The effect of LSD on the brain is unique, profound, and very well researched. LSD acts on specific brain receptors and networks, causing perception, emotions, and consciousness to temporarily and fundamentally change. These neurobiological changes explain the rich visual and emotional experience, as well as the therapeutic potential.

What does LSD take effect on?

The most important place where LSD works is the 5-HT2A receptor. This is a serotonin receptor that is abundant in the cortex. LSD is a very potent partial agonist of this receptor. If you block this receptor with an antagonist such as ketanserine, both the subjective trip experience and the measurable changes in brain activity disappear.

Additionally, LSD binds to a lesser extent to receptors such as 5-HT1A, 5-HT2C, dopamine D2, α2-adrenergic receptors, and the recently identified TAAR1. These contribute primarily to the later phases of the trip, with mild sympathetic activation or motor restlessness.

What happens in the brain during an LSD trip?

Functionally, LSD lowers the internal network coherence of the Default Mode Network (DMN), particularly in the posterior cingulate cortex and medial prefrontal cortex. At the same time, the connectivity between networks to. This leads to a looser hierarchical structure in the brain and a state of increased network entropy — with more brain states and thus more flexibility in thinking and feeling.

In the sensory and visual cortex, hyperconnectivity actually arises. The primary visual cortex (V1–V4) shows increased blood flow and communication, which correlates strongly with visual hallucinations. The thalamus—which normally filters sensory input—shows looser 'gating' under LSD, allowing raw sensory information to reach the cortex more easily.

In the limbic system, particularly the amygdala and hippocampus, reactivity to fear stimuli decreases. This contributes to emotional processing and increased empathy, an effect that is also important in therapeutic contexts.

Which receptors control this process?

1. 5-HT2A on pyramidal cells → increased glutamate release, dysregulation of top-down control, increased sensory input.
2. 5-HT1A → inhibits serotonergic tone, supports introspective phases.
3. D2 → contributes to delayed agitation or possible delusions at high doses.
4. CAKE1 → influences dopamine and adrenaline release, role only recently recognized.

In summary: LSD works primarily through 5-HT2A receptors in brain regions such as the DMN, prefrontal cortex, visual cortex, and thalamus. It leads to DMN disintegration, increased network connectivity, more sensory input and high entropy in brain activity. These changes explain the onset of ego dissolution, hallucinations, and creative insights — the typical characteristics of an LSD experience.

More detailed explanation about this topic can be found on the page about the effects of LSD.

Biochemical mechanism of action

LSD binds primarily to 5-HT2A receptors, a subtype of serotonin receptor that is common in the cortex. This binding disrupts normal signal transmission in brain cells and alters the balance between stimuli that are normally transmitted more strongly or, conversely, more weakly.

In addition, LSD also binds to other receptors, such as 5-HT1A, 5-HT2C, dopamine D2, adrenergic receptors and TAAR1; these appear to be involved in later or more subtle effects, such as mild physical arousal, altered mood and, in some cases, restlessness.

At the cellular level, LSD primarily causes cortical pyramidal cells to fire differently, leading to increased glutamate release and altered network activity. This makes the brain less “strictly regulated” than usual and allows more scope for unusual associations and perceptions.

Networks in the brain

Under the influence of LSD, the cohesion within the Default Mode Network , particularly in areas involved in self-reflection, inner monologue and a stable sense of “self”. At the same time, the connectivity between different brain networks increases, meaning that information is processed in a less compartmentalised and more integrated way.

The thalamus normally filters a great deal of sensory input before it reaches the cortex. Under the influence of LSD, this filtering appears to become less stringent, allowing more sensory information and internal signals to get through and be experienced more consciously.

Activity is also often heightened in the visual cortex, which is consistent with the pronounced visual effects such as colour intensification, moving patterns and distortion of shapes.

Emotions and experience

LSD can reduce the amygdala’s reactivity to fear-inducing stimuli, which for some people leads to a reduced sense of threat, greater emotional openness and, at times, a feeling of relief or release. This is also one reason why some therapeutic applications are considered promising.

The change in neural activity can lead to a more flexible, sometimes chaotic train of thought, but also to new insights, connections and a strong sense that you are seeing things “from a different perspective”.

What someone experiences

The experience is often a combination of sensory, cognitive and emotional changes. Common descriptions include:

1. Enhanced colours and patterns.

2. The distortion of time, space and depth.

3. More associative thinking and, at times, synaesthesia-like effects.

4. More intense emotions, ranging from euphoria to fear.

5. A sense of connection, wonder or introspection.

At higher intensities, the sense of self may temporarily weaken, causing a person to feel less firmly attached to their usual self-image. This can be experienced as liberating, mystical or, conversely, overwhelming.

Physical effects

As well as the mental effects, there are often physical signs too, such as dilated pupils, increased alertness, a slight rise in heart rate, tension or an “electric” sensation in the body. The trip can therefore be quite intense, not only mentally but also physically.

The duration of an LSD trip is relatively long compared with many other psychedelics, meaning that the experience often lasts for hours and unfolds in phases: the onset, the peak, the plateau and the gradual comedown.

In short

In short: LSD not only alters mood or perception, but also temporarily changes the way brain cells, receptors and networks interact, causing the brain’s filtering function to become less rigid and leading to significant shifts in perception, emotion and sense of self.