NutriStack
Fluoxetine and Psilocybin, a caution.
Fluoxetine substantially blunts psilocybin's psychedelic effects through chronic 5-HT2A receptor downregulation, and its very long half-life means the effect persists for weeks after stopping. There is also a theoretical risk of serotonin syndrome with combined serotonergic load.
One pair, every claim cited. The two substances, the type, the mechanism, the recommendation, and the primary literature.
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From the interaction database
What the row says.
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At a glance
- Substances
- Fluoxetine and Psilocybin
- Pair type
- Caution
- Evidence (highest tier)
- Emerging
- Source citations
- 2 sources
- Stack Score effect
- −5 to your Stack Score (per scored caution row).
- Scope
- Supplement × Prescription
- Last verified
- May 30, 2026
Caution · Emerging evidence
Caution
What is happening. Fluoxetine substantially blunts psilocybin's psychedelic effects through chronic 5-HT2A receptor downregulation, and its very long half-life means the effect persists for weeks after stopping. There is also a theoretical risk of serotonin syndrome with combined serotonergic load.
Mechanism. Chronic SSRI exposure downregulates 5-HT2A receptors and raises baseline synaptic serotonin, attenuating psilocin's 5-HT2A agonism. Fluoxetine's long elimination half-life extends this attenuation well past discontinuation.
Recommendation. Do not take psilocybin while on fluoxetine. Because fluoxetine and norfluoxetine have half-lives of 1-2 weeks and 1-2+ weeks respectively, wait at least 5 weeks after the last fluoxetine dose before any psilocybin exposure.
Stack Score
How this pair moves the number.
Effect on the composite score
If both Fluoxetine and Psilocybin are in the same stack, this pair applies −5 to your Stack Score (per scored caution row).
The full algorithm, the clamping rules, and four worked stacks are documented at /methodology/stack-score.
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