Interactions between classic psychedelics and serotonergic antidepressants: Effects on the acute psychedelic subjective experience, well-being and depressive symptoms from a prospective survey study

Classic psychedelics such as psilocybin, LSD, DMT and mescaline have seen a renewed research interest because controlled administration can produce rapid and sometimes sustained symptom improvements in depression, OCD and anxiety disorders. Many clinical participants are already prescribed serotonergic antidepressants (selective serotonin reuptake inhibitors, SSRIs, and serotonin–noradrenaline reuptake inhibitors, SNRIs), and earlier case reports and observational work have suggested that chronic SRI use can attenuate the subjective effects of psychedelics. Conversely, a recent randomised trial of 14-day escitalopram pre-treatment in healthy volunteers found reduced physiological and some negative effects of psilocybin but no reduction in positive subjective effects, leaving the interaction between SRIs and psychedelics uncertain. Barbut Siva and colleagues set out to address this gap using prospectively collected survey data from naturalistic psychedelic experiences. The study compared acute subjective psychedelic effects and before–after changes in well-being and depressive symptoms between people with self-reported psychiatric diagnoses who were currently taking SRIs ('SRI +') and those who reported no lifetime psychiatric medication use ('SRI -'), aiming to inform trial design and clinical practice for psychedelic-assisted interventions.

Data were pooled from three web-based prospective cohorts run by the Centre for Psychedelic Research: a large automated prospective cohort (Cohort 1), a modified follow-up cohort (Cohort 2) and a ceremony/retreat study (Cohort 3). Recruitment relied on online platforms and retreat centre advertisements. All studies had ethical approval from Imperial College London. Subjects were aged 18 or older, English-speaking and planning to take a classic serotonergic psychedelic (psilocybin/magic mushrooms/truffles, LSD/1P-LSD, DMT/5‑MeO‑DMT, ayahuasca). For the present analysis only participants who self-reported at least one psychiatric diagnosis and who used a classic psychedelic on the indexed occasion were included. Participants were classified into two groups based on self-reported medication history: 'SRI -' (never treated with psychiatric medication) and 'SRI +' (currently taking an SRI). Data collection focused on three time points: baseline (about 1 week pre-experience) for demographics, psychiatric history, intentions and baseline WEMWBS and QIDS‑SR‑16 scores; one day post-experience for drug type, estimated dose, setting and subjective experience measures; and four weeks post-experience for follow‑up WEMWBS and QIDS‑SR‑16. The study excluded experiences involving compounds outside the listed classic psychedelics and standardised dose categories using estimated LSD-equivalents. Acute subjective facets were measured one day post-experience using validated instruments: the Mystical Experience Questionnaire (MEQ), Challenging Experience Questionnaire (CEQ), Emotional Breakthrough Inventory (EBI) and the ASC-Vis visual subscale. Well-being was measured with the WEMWBS and depressive symptoms with the QIDS‑SR‑16 at baseline and 4 weeks. Potential confounders (dose, prior psychedelic use, intentions, setting elements) were identified via t-tests and checked for multicollinearity using variance inflation factors (VIF cutoff 5). For the primary analysis, a multivariate analysis of covariance (MANCOVA) was run with MEQ, CEQ, EBI and ASC-Vis as dependent variables and SRI status as the independent variable, controlling for identified covariates; Pillai's trace was used as the test statistic. For secondary analyses, linear mixed-effects models predicted WEMWBS and QIDS‑SR‑16 scores over time (baseline and 4 weeks) including Time, Condition (SRI +/‑) and their interaction. Analyses were performed in IBM SPSS and R using lme4 and related packages.

From an initial 1,463 registrants across cohorts, 161 participants met inclusion criteria (self-reported psychiatric diagnosis and use of a classic psychedelic) and completed the required timepoints for at least some analyses. Of these, 98 participants reported no lifetime psychiatric medication use ('SRI -') and 63 reported current SRI use ('SRI +'). Psilocybin was the most commonly used psychedelic, followed by LSD. Depression and anxiety were the predominant diagnoses, reported by 73% of 'SRI -' and 97% of 'SRI +' participants. Baseline WEMWBS and QIDS‑SR‑16 scores did not differ significantly between groups. Potential confounders that differed between groups included age (SRI + older), higher therapeutic intention among SRI +, and greater prior psychedelic frequency, curiosity, connection with nature, music use and emotional support among SRI -. Psychedelic dose did not differ between groups and VIF checks supported inclusion of the identified covariates in multivariate models. Primary outcomes (acute subjective experience): 131 participants completed the one‑day post questionnaires (84 SRI -, 47 SRI +). MANCOVA controlling for covariates indicated a significant Condition effect on the combined subjective measures (p = 0.016, partial ηp2 = 0.09). Follow-up univariate tests showed that SRI + participants had significantly lower scores on the MEQ (F(1,124) = 3.997, p = 0.048, ηp2 = 0.03), CEQ (F(1,124) = 10.618, p = 0.001, ηp2 = 0.08) and EBI (F(1,124) = 5.772, p = 0.018, ηp2 = 0.04). There was no significant between-group difference on ASC-Vis (F(1,124) = 1.666, p = 0.199, ηp2 = 0.01). Numerically, the authors report SRI - participants had approximately 18.2% higher mystical scores, 50.9% higher challenging scores and 31.9% higher emotional breakthrough scores than SRI + participants. Secondary outcomes (well-being and depressive symptoms): 92 participants completed baseline and 4-week follow-up (59 SRI -, 33 SRI +). Linear mixed models found a significant main effect of time for both WEMWBS and QIDS‑SR‑16 (p < 0.001), indicating overall improvement after the psychedelic experience. However, Time × Condition interactions were non-significant for WEMWBS (p = 0.47) and for QIDS‑SR‑16 (p = 0.39), indicating comparable pre–post improvements in well-being and depressive symptoms across SRI - and SRI + groups. The authors note attrition and that several planned covariates were controlled for in these models.

Barbut Siva and colleagues interpret their findings as showing that concurrent SRI use is associated with reduced intensity of several emotional components of the acute psychedelic experience—mystical-type experiences, challenging experiences and emotional breakthroughs—while leaving drug-induced visual phenomena unchanged. The pattern suggests that SRI use may blunt emotional responsiveness during the acute experience rather than producing a broad suppression of perceptual effects. The authors compare their results with previous reports and trials. They note consonance with earlier case reports and observational data indicating attenuated subjective responses among chronic SRI users, and partial divergence from a recent escitalopram pre-treatment trial in healthy volunteers that found no reduction in positive subjective effects. Possible mechanisms discussed include chronic SRI-induced desensitisation or down-regulation of 5‑HT2A receptors, which are implicated in psychedelic effects, but the absence of changes in visual effects argues against a simple global 5‑HT2A down-regulation explanation. An alternative hypothesis proposed is SRI-associated emotional blunting, which could specifically reduce emotionally laden components of the psychedelic experience while sparing perceptual alterations. Despite attenuated acute emotional effects among SRI + participants, the study found similar improvements in depressive symptoms and well-being across groups at 4 weeks. The authors suggest several interpretations: the reductions in subjective intensity may not have been large enough to impede therapeutic benefit; the link between acute subjective intensity and longer-term improvement may not be straightforward; or SRI co‑administration might still permit clinical benefit. In clinical terms, these results are discussed in the context of whether patients should discontinue SRIs before psychedelic-assisted therapy. The investigators highlight practical concerns about discontinuation—possible withdrawal symptoms and loss of stability—and suggest that continuing SRIs, tapering more slowly or employing partial tapering strategies might be alternatives worth evaluating. Key limitations acknowledged by the authors include the exploratory, non‑pre-registered nature of analyses, unequal group sizes and sample attrition, reliance on self-reported SRI use without biochemical verification and absence of data on duration of SRI treatment or whether participants paused medication prior to the psychedelic event. They also note that the sample tended to report mild to moderate depressive symptoms and that dose estimates were self-reported rather than objectively measured, limiting generalisability and causal inference. The authors therefore call for controlled clinical studies to clarify pharmacological and clinical interactions between SRIs and psychedelics.

The study concludes that people currently medicated with SRIs reported significantly less intense mystical, challenging and emotional breakthrough experiences during naturalistic psychedelic use compared with those never treated with psychiatric medication. Despite these acute subjective differences, both groups showed comparable improvements in depressive symptoms and well-being at 4 weeks. The authors characterise the findings as exploratory, derived from uncontrolled, self-reported data, and emphasise the need for controlled research in clinical populations to guide best practice for psychedelic-assisted therapy implementation.