Attenuation of psilocybin mushroom effects during and after SSRI/SNRI antidepressant use.

Background: Psilocybin is being studied for depression, but little is known about how it interacts with common antidepressants. Limited data suggest that psilocybin's effects may be diminished by serotonergic antidepressants acutely and even after a medication washout period.

Aims: To learn the extent to which antidepressants may diminish the effects of psilocybin-containing mushrooms both concurrently and after discontinuation of antidepressants.

Methods: Online retrospective survey of individuals with use of psilocybin mushrooms (1) with an antidepressant and/or (2) within 2 years of discontinuing an antidepressant. Participants who took mushrooms with an antidepressant and either took the same dose pre-antidepressant or took the same dose with other people not on antidepressant reported the strength of drug effects relative to their expectation. Participants who took mushrooms following discontinuation of an antidepressant also reported the presence of weakened effects.

Results: In reports ( = 611) of taking mushrooms with an antidepressant, probabilities [95% CI] of weaker than expected drug effects were 0.47 [0.41-0.54] (selective serotonergic reuptake inhibitors, SSRIs), 0.55 [0.44-0.67] (serotonin norepinephrine reuptake inhibitors, SNRIs) and 0.29 [0.2-0.39] (bupropion). Following SSRI/SNRI discontinuation ( = 1,542 reports), the probability of reduced drug effects was not significantly different from the earliest post-discontinuation timepoint (within 1 week) until 3-6 months, probability = 0.3 [0.20-0.46],  = 0.001. A sensitivity analysis found that removing responses involving fluoxetine, which has an especially long half-life, did not significantly alter this result.

Conclusions: SSRI/SNRIs appear to weaken psilocybin drug effects relative to a non-serotonergic antidepressant. This dampening effect may last as long as 3 months following antidepressant discontinuation.