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Serotonergic psychedelics (also known as serotonergic hallucinogens) are a class of hallucinogenic drugs with a method of action strongly tied to the serotonin neurotransmitter. Serotonin (often referred to as 5-HT, short for its full chemical name 5-Hydroxy Tryptamine) is a naturally occurring neurotransmitter which is tied to positive mood, certain involuntary muscle control, and countless other functions, many of which are not yet fully understood.
Method of action 
While the method of action of serotonergic psychedelics is not fully understood, serotonergic psychedelics are known to show affinities for various 5-HT receptors in different ways and levels, and may be classified by their activity at different 5-HT sub-sites, such as 5-HT1A, 5-HT1B, 5-HT2A, etc. Many serotonergic psychedelics, such as the family of tryptamines, have very strong structural similarities to serotonin itself, which partially explains the affinity for certain 5-HT sites. It is almost unanimously agreed that serotonergic psychedelics produce their effect by acting as strong partial agonists at the 5-HT2A receptors. How this produces the psychedelic experience is unclear, but it is likely that it acts by increasing excitation in the cortex, possibly by specifically facilitating input from the thalamus, the major relay for sensory information input to the cortex. Worth noting is that selective serotonin reuptake inhibitors (a class of antidepressants including Paxil, Prozac, and Zoloft) can increase the dosage required for hallucinogenic effects of serotonergic psychedelics, in some people, based on anecdotal reports. Some users, however, have found this to be entirely untrue for them.
Examples of serotonergic psychedelics include DMT, LSD, psilocybin, and mescaline. The tryptamine psychedelics, such as DMT and psilocybin structurally resemble serotonin itself. The phenethylamine psychedelics on the other hand, such as mescaline (found naturally in peyote) and compounds of the 2C family, more closely resemble the neurotransmitter dopamine.
Recreational uses 
External resources 
- Organization for Understanding Cluster Headaches Research Library - 5HT and Hallucinogens (Archive.org index, Aug 28, 2005)
- Cluster Busters