Psilocybin and cyproheptadine
Reduces effectsAntihistamine, 5-HT2A antagonist · also: periactin, peritol
Cyproheptadine is a serotonin and histamine blocker that would be expected to reduce a mushroom experience and cause sedation, but it has not been tested as a psilocybin blocker in people.
Reduces the experience and adds sedation. It is also the drug used to treat serotonin syndrome.
Claims re-checked against the cited sources:
Why it happens
Cyproheptadine is a first-generation antihistamine that also blocks serotonin receptors, with anticholinergic and sedative effects. Because psilocybin acts through 5-HT2A receptors, a serotonin antagonist would be expected to blunt it, as ketanserin does in human studies. It is used as an adjunct in treating serotonin syndrome, though evidence that it changes outcomes is limited.
What is known
Its receptor profile is well established; it is the standard antidote in serotonin toxicity.
- 2026
- The US label describes cyproheptadine as a serotonin and histamine antagonist with anticholinergic and sedative effects. Cyproheptadine hydrochloride tablet US prescribing information, DailyMed
- 1998
- In a case series of five serotonin syndrome patients given 4 to 8 mg oral cyproheptadine, signs resolved in all, but the authors state its role is undefined and it is unknown whether it modifies outcome. Graudins, Stearman & Chan, Journal of Emergency Medicine 1998
- 1998
- Psilocybin's effects in humans were blocked dose-dependently by the 5-HT2A antagonist ketanserin. Vollenweider et al., NeuroReport 1998
Safety guidance
- Not a reliable or tested trip terminator; reassurance and a calm setting come first.
- Expect drowsiness, dry mouth and possible confusion from its anticholinergic effects.
- Do not combine with alcohol or other sedatives.
- If you take it on prescription, do not change your dose without your prescriber.
When to seek help
Seek help for confusion, a very fast heartbeat, inability to urinate, or extreme drowsiness after taking cyproheptadine. Emergency red flags.
Common questions
Will cyproheptadine stop a mushroom trip?
It may blunt it because it blocks serotonin receptors, but no human study has tested it with psilocybin.
Is it the antidote for serotonin syndrome?
It is commonly used as an adjunct, but evidence that it improves outcomes is limited.
Is it dangerous with mushrooms?
No specific danger is documented; the main issues are sedation and anticholinergic side effects.
Sources
How we research this: sources, evidence grading, review and updates.