Can I have breakfast right before a psychedelic session?
It is generally better not to eat right before a session. It is recommended not to eat any food for at least 4 hours before the session. This is because the digestion process of food requires energy and blood flow to the digestive organs, which can affect the effects of the psychedelic substance. Additionally, eating right before a psychedelic session can slow down the absorption of psychedelic substances and can cause nausea or vomiting. Eating a light meal about 4 hours before your psychedelic session is acceptable so that you have enough energy for the session. However, if it is too difficult to stay sober for 4 hours, or if you have diabetes or are prone to fainting, you may want to eat some fruit, with the exception of bananas.
Psychedelic sessions: Psychedelic therapy | Psychedelic ceremonies

Having breakfast right before a psychedelic session, like a truffle session or a MDMA session, is generally advised against. According to multiple experiences and recommendations on the Triptherapie forum, It is advisable not to eat for at least 3 to 4 hours before the start of the session. There are several reasons for this:
Firstly, the body uses energy and blood supply for digestion, which can flatten or slow down the effects of psychedelics such as psilocybin. Additionally, eating immediately before the session increases the likelihood of nausea and vomiting, which occurs particularly in the first 30 minutes after ingestion.
If your session starts at 10:00 AM, for example, it is advisable to eat your last meal before 6:00 AM. If you follow a medical diet, have diabetes, or are prone to low blood sugar, a very light breakfast such as a piece of fruit (not a banana) or a small portion of yogurt and/or oatmeal approximately 60–90 minutes before the start might be a better option.
Preferably, also do not drink coffee or dairy immediately before the session and avoid heavy or fatty meals. Do ensure that you are sufficiently hydrated, without drinking large amounts just before the session.
I have eaten quite a lot before a truffle session, and it is not ideal. The nausea is worse, but you won't die from it or anything.