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

Gukasyan and colleagues situate the study within growing interest in psilocybin-assisted therapy for major depressive disorder, noting that clinical trials commonly require discontinuation of serotonergic antidepressants prior to psychedelic administration. Prior reports—largely from LSD studies, small clinical samples, and anecdotal sources—have suggested that monoaminergic antidepressants, particularly SSRIs and MAOIs, can attenuate classic psychedelic effects or, conversely, sometimes potentiate them depending on the drug class. There is also theoretical concern about interactions such as serotonin syndrome, but empirical data on psilocybin specifically are limited and mixed. The study therefore aimed to quantify two practical questions in a large naturalistic sample: (1) whether taking an antidepressant concurrent with psilocybin-containing mushrooms is associated with reduced subjective drug intensity, and (2) whether any reduction in subjective intensity persists after discontinuation of antidepressants and for how long. The investigators also collected data on self-reported adverse events, including possible serotonin syndrome. The work is a retrospective online survey intended to capture naturalistic experiences across a broad population of mushroom users with recent or concurrent antidepressant exposure.

The researchers conducted an anonymous web-based survey between September 2020 and November 2021, recruiting via forums, subreddits, and social media related to psychedelics and mental health. Major inclusion criteria were age over 18, English literacy, and having used a moderate or high dose of psilocybin mushrooms either while taking an antidepressant or within two years after stopping one. Respondents provided demographic and diagnostic history and could report experiences before, during, and/or after antidepressant use; those who reported during-use or post-discontinuation experiences entered separate survey streams labelled here as Survey 1 and Survey 2. Responses from duplicate IP addresses and low-quality responses were excluded. Survey 1 (psilocybin while on antidepressants) captured episode-level details for those with one or two such experiences and asked participants to report the antidepressant used (selected from a dropdown or free text), the form and estimated dose of psilocybin, whether the same dose had been taken prior to antidepressant initiation or by peers not on antidepressants, duration of antidepressant use, and whether a ‘‘drug holiday’’ (skipping doses) had occurred. For episode-level analysis the investigators restricted to dried mushroom use with resolvable gram doses and to episodes involving SSRIs, SNRIs, or bupropion (NDRI). The primary outcome for Survey 1 was participant-reported drug effect relative to expectation collapsed into a binary indicator of ‘‘weaker than expected’’ (including ‘‘no effect at all'') versus not. Survey 2 (psilocybin after discontinuation) asked respondents to indicate how long after stopping an antidepressant they used psilocybin (six time windows from within 1 week to ≥12 months), the antidepressant previously used, duration of prior antidepressant treatment, concurrent medications or other substances at the time of psilocybin use, anticipated intensity and actual intensity relative to expectation, and whether additional doses were taken because effects felt weak. For both surveys the primary analysis used logistic regression models predicting reduced subjective effects. Predictor covariates included age, sex, antidepressant class (Survey 1), psilocybin dose (Survey 1), duration of antidepressant use, drug holiday (Survey 1), time since discontinuation (Survey 2), anticipated intensity (Survey 2), and concurrent drug use. Regression coefficients were exponentiated to odds ratios and converted to probabilities for interpretation. Sensitivity analyses removed episodes involving other psychoactive drugs and separately examined cases involving fluoxetine because of its long half-life. Dose entries given as informal measures were converted to grams when possible; non-resolvable dose reports were excluded from episode-level analyses.

Sample recruitment yielded 2,625 completed, non-excluded surveys. The sample was predominantly white (91%), male (55%), mostly located in the United States (72%), and more than half held at least a bachelor's degree (54%). Survey 1 (psilocybin while on antidepressants): Of the 2,625 completers, 1,942 reported taking a moderate to high dose of psilocybin while on an antidepressant. Analyses of individual, episode-level reports were restricted to participants who had one or two such episodes and met additional inclusion criteria (same-form dried mushrooms, quantifiable gram dose, use of SSRI/SNRI/NDRI, and no other psychoactive prescription medications). After sequential exclusions for form, unquantifiable dose reports, uncommon antidepressant classes, and concurrent prescribed psychoactive medications, the final analytic set comprised 611 episodes from 468 participants. Concurrent use of other non-prescription psychoactive drugs was common (59.2% of episodes) and retained in the main analysis; removing those episodes in a sensitivity analysis did not materially change results. A main effect of antidepressant drug class on the probability of reporting a weaker-than-expected psilocybin effect was statistically significant (p < 0.001). Adjusted probabilities of reporting weaker-than-expected effects were 0.47, 95% CI [0.40, 0.54] after SSRIs; 0.55, 95% CI [0.44, 0.67] after SNRIs; and 0.29, 95% CI [0.20, 0.39] after bupropion. Sex, age, psilocybin dose, duration of antidepressant use, and presence of a drug holiday were not significant predictors in the model. Restricting attention to the most commonly reported antidepressants (escitalopram and sertraline) and including dose and dose × duration interactions likewise failed to show significant dose or time effects. On broader, non-episode-specific questions among 1,062 respondents who had used psilocybin both on and off antidepressants, 549 (51.7%) reported reduced intensity when on antidepressants, 313 (29.5%) reported about the same intensity, and 72 (6.8%) reported more intense effects. Of the 549 who reported reduced intensity, 284 (51.7%) attempted to overcome this by taking a larger dose; of those, 129 (45.4%) reported success and 155 (54.6%) did not. Drug holiday was uncommon in the episode-level sample (12.8% reported any days off) and showed no reliable effect. Adverse events attributed to combining psilocybin and an antidepressant were reported by 110 respondents (5.7%), but free-text review suggested many of these did not describe true adverse events; a conservative estimate was 4.0% reporting an adverse event. Fifty-five participants (2.8%) believed they had developed serotonin syndrome after reading a provided description, but only eight participants both believed they had serotonin syndrome and also reported an adverse reaction attributable to the combination—equivalent to 0.4% of those who combined psilocybin and an antidepressant in the sample. Survey 2 (psilocybin after discontinuation): Of 2,625 completers, 1,354 reported psilocybin use after discontinuing an antidepressant yielding 1,955 episodes; after exclusions focusing on SSRI/SNRI prior use and episode-level data quality, the final analytic set comprised 1,542 episodes in 1,092 participants. Absolute prevalence of weaker-than-expected effects by time since discontinuation were: within 1 week 32.7% ± SE 4.6; 1 week–1 month 25.9% ± SE 2.7; 1–3 months 23.3% ± SE 2.3; 3–6 months 15.7% ± SE 2.3; 6–12 months 18.8% ± SE 2.4; and ≥12 months 15.6% ± SE 2.1. In the logistic regression model, the probability of reduced effects was significantly lower beginning at the 3–6 month time window (probability = 0.30, 95% CI [0.20, 0.42], p = 0.001) and remained lower thereafter. Older age was associated with a higher likelihood of reduced effects after discontinuation (p = 0.012). Prior use of multiple psychiatric medications was associated with higher likelihood of reduced effects (probability = 0.58, 95% CI [0.52, 0.65], p = 0.014). Unexpectedly, duration of prior antidepressant treatment >12 months was associated with a lower probability of reduced effects compared with the shortest duration group (<1 month) (probability = 0.35, 95% CI [0.23, 0.49], p = 0.033). Anticipated moderate or strong drug intensity was associated with lower odds of reporting reduced effects relative to milder anticipated intensity. A sensitivity analysis excluding fluoxetine cases (n = 320) did not materially change the primary timing result.

The investigators interpret their findings as indicating that concurrent SSRI and SNRI use is associated with attenuated subjective effects of psilocybin-containing mushrooms for a substantial minority of users—about half in episode-level analyses and roughly half in broader self-reports—whereas a non-serotonergic antidepressant (bupropion) was associated with lower rates of attenuation. This attenuation rate is lower than some earlier LSD-focused reports, and the authors suggest this difference may reflect either sample size and method variation or genuine pharmacological differences between substances. They note few self-reported adverse events attributable to the combination and very few reports consistent with serotonin syndrome, observing that serious serotonin toxicity appears rare in their sample. The analyses did not find that higher antidepressant dose or longer concurrent duration reliably increased the likelihood of attenuation, nor that brief ‘‘drug holidays’’ reliably restored psilocybin effects. In the post-discontinuation sample the likelihood of reduced effects decreased over time but remained apparent for up to 1–3 months after stopping SSRIs/SNRIs; sensitivity analyses removing fluoxetine cases (which has a long half-life) did not change this pattern, leading the authors to propose that longer-term receptor-level changes such as 5-HT2A downregulation may underlie the effect rather than simple residual drug presence. The authors discuss inconsistency with some prior controlled and clinical findings and acknowledge that treatment-resistant populations may show different patterns. Clinically and ethically, they emphasise the importance of weighing risks of antidepressant discontinuation—withdrawal and relapse—against potential attenuation of psychedelic effects, suggesting that more precise quantification of attenuation could inform decisions about whether to taper, delay, or adjust psilocybin dosing. The proposed mechanism centres on 5-HT2A receptor downregulation following serotonergic antidepressant exposure, though the authors acknowledge some conflicting literature on receptor binding changes in humans. Key limitations are emphasised: the retrospective anonymous online design is vulnerable to recall and selection biases; self-reported diagnoses and adverse events could not be clinically verified; effect magnitude could not be precisely quantified from categorical subjective reports; variability in psilocybin content of mushrooms and uncontrolled contextual factors (set and setting) limit interpretation; and diagnostic history and treatment resistance were not accounted for in the analyses. The authors conclude that while their results point to attenuation of psilocybin effects during and for some months after SSRI/SNRI use, controlled prospective studies and clinical data are needed to determine clinical implications and optimal approaches to antidepressant management in the context of psychedelic-assisted treatments.