Psilocybin Drug Interaction Safety Matrix

MAOIs prevent breakdown of serotonin and other monoamines. Combined with psilocybin this creates serotonin toxicity risk (agitation, hyperthermia, seizures, and in severe cases death). Even at sub-toxic doses, intensity is dramatically amplified and duration extended beyond what most people can safely navigate.

Sources: Passie et al. 2002 | Clinical trial exclusion criteria across all major trials

Multiple case reports document seizures when lithium is combined with classical psychedelics including psilocybin. The mechanism is incompletely understood but may involve altered neuronal excitability. Every major psilocybin clinical trial protocol lists lithium as an absolute exclusion criterion.

Sources: Nayak et al. 2021 Safety Review | COMPASS Pathways Phase 2 exclusion criteria

Tramadol has significant serotonergic activity beyond its opioid effects — it inhibits serotonin and norepinephrine reuptake, creating serotonin syndrome risk when combined with psilocybin. Additionally, tramadol independently lowers the seizure threshold, compounding neurological risk.

Sources: Boyer EW 2012 — Serotonin Syndrome Review | Clinical pharmacology literature

Antipsychotics work partly by blocking 5-HT2A receptors — the same receptors psilocybin activates. Most antipsychotics will partially or completely block psilocybin's perceptual effects. Second-generation (atypical) antipsychotics also carry QT-prolongation cardiac risks. Beyond futility, antipsychotics are prescribed for serious psychiatric conditions; stopping them without supervision is dangerous.

Sources: Vollenweider et al. 1998 — Ketanserin blocking of psilocybin effects

TCAs have serotonergic activity that creates additive risk with psilocybin. Clomipramine (the most serotonergic TCA) poses the greatest concern for serotonin syndrome. All TCAs have cardiac effects — QT prolongation and arrhythmia risk — that may be relevant during physiologically activating psychedelic states.

Sources: Clinical pharmacology review | Grob CS 2002 case series protocols

Anticonvulsants vary widely in interaction risk. Lamotrigine appears to blunt psilocybin effects in some users via 5-HT3 antagonism. Carbamazepine is a strong CYP450 inducer that can significantly alter psilocybin metabolism. Valproate affects multiple enzyme pathways with broad CNS effects. Stopping anticonvulsants without supervision risks seizures.

Sources: Carhart-Harris et al. protocol exclusion criteria | CYP450 interaction literature

Chronic SSRI use causes 5-HT2A receptor downregulation, which blunts psilocybin's effects. Some people report complete blockade. Fluoxetine (Prozac) has an extremely long half-life — its active metabolite norfluoxetine takes 4–6 weeks to clear. Other SSRIs clear in 1–2 weeks. There is theoretical low-level serotonin syndrome risk at high doses, though well-documented cases are rare.

Sources: Bonson et al. 1996 — Serotonergic modulation | Vollenweider 2010

SNRIs affect serotonin reuptake similarly to SSRIs with the same concerns: blunted psilocybin effects and theoretical (low) serotonin syndrome risk. Venlafaxine (Effexor) is particularly challenging because discontinuation syndrome is severe even after a short taper — dizziness, electric shock sensations ('brain zaps'), nausea.

Sources: Clinical pharmacology literature | Passie T 2008

The psilocybin + cannabis interaction is one of the most common reported and one of the most unpredictable. THC can potentiate both intensity and duration significantly. In people prone to anxiety, this potentiation substantially increases the risk of a difficult or overwhelming experience. CBD alone appears to have minimal interaction and some facilitators use it for grounding.

Sources: Johnson & Griffiths 2017 | Facilitator consensus guidance

Alcohol is not acutely dangerous in combination with psilocybin, but it is a CNS depressant that blunts the presence and emotional openness that makes psilocybin sessions therapeutic. Alcohol after a session disrupts sleep and integration — the 24–48 hour post-session period is considered critical for integration, and alcohol consumption during this window appears to reduce lasting benefit.

Sources: Harm reduction consensus | Watts et al. 2017 integration research

Prescribed stimulants (Adderall, Ritalin) add cardiovascular strain to psilocybin's mild increases in heart rate and blood pressure — relevant especially for people with underlying cardiac conditions. MDMA adds serotonergic load creating elevated serotonin syndrome risk and places substantial physiological demand on the body. Cocaine and methamphetamine pose significant cardiovascular risks.

Sources: Carhart-Harris & Nutt 2010 | Pharmacology literature

Opioids don't cause acutely dangerous reactions with psilocybin in most cases, but opioid-induced sedation and emotional blunting significantly impairs the therapeutic experience and integration capacity. Methadone prolongs QT interval (cardiac risk in combination with any physiologically activating substance). Buprenorphine's complex pharmacology adds uncertainty.

Sources: Harm reduction literature | Methadone cardiac review: Diaz 2011

Benzodiazepines dampen psilocybin effects significantly. This is clinically useful — facilitators often have benzos available for crisis management, as they can reduce session intensity within 20–30 minutes. For regular benzo users, psilocybin effects will be blunted. Note: abrupt discontinuation of high-dose long-term benzodiazepine use carries its own serious risks including seizures.

Sources: Nichols 2016 | Clinical trial safety protocols (benzos listed as rescue medication)

Beta blockers dampen the sympathetic 'fight or flight' response. Propranolol has been studied specifically for reducing anxiety during psilocybin sessions and can blunt cardiovascular responses (heart rate, blood pressure). Some research suggests it may reduce the overall psychedelic experience. Occasionally used intentionally by facilitators for very anxious participants.

Sources: Hasler et al. 2004 | Carhart-Harris et al. 2018

Nausea is a common psilocybin side effect in the first 1–2 hours. Ondansetron (Zofran) or ginger are commonly used for nausea prevention by facilitators. Diphenhydramine and promethazine have mild anticholinergic effects that may slightly modify the experience. These are generally low-concern interactions.

Sources: Johnson et al. 2019 Johns Hopkins protocol | Facilitator consensus

The Stamets Stack — microdose psilocybin + lion's mane mushroom + niacin — is widely used in the microdosing community. Lion's mane has documented nerve growth factor (NGF) stimulating effects. Flush niacin (nicotinic acid) is hypothesized to potentiate the combination via vasodilation. No adverse interactions have been clinically documented.

Sources: Stamets 2019 patent | Mori et al. 2009 (lion's mane NGF) | Limited human trial data

Caffeine has minimal pharmacological interaction with psilocybin. However, caffeine's anxiogenic effects may compound the anxiety that some people experience during sessions. Habitual users should have small amounts to avoid withdrawal headache rather than none.

Sources: Facilitator consensus

Ketamine and psilocybin are sometimes used in complementary clinical programs in separate sessions. There is minimal data on concurrent use. Both can produce dissociative effects; ketamine works via NMDA receptor antagonism (different from psilocybin's 5-HT2A mechanism). The combination is theoretically complex — synergistic or additive effects are plausible but lack clinical study.

Sources: Limited published data | Expert consensus only