Drug-drug interactions between psychiatric medications and MDMA or psilocybin: a systematic review

Sarparast and colleagues situate this review within a renewed clinical interest in MDMA and psilocybin as adjuncts to psychotherapy for disorders such as post‑traumatic stress disorder and major depressive disorder. Both compounds differ from typical psychiatric medications in being administered only a few times during a treatment course and have advanced in the US FDA pipeline (MDMA with Breakthrough Therapy designation for PTSD; psilocybin for depression). Because current standard care for these indications frequently involves ongoing use of psychiatric medications and because MDMA and psilocybin both modulate serotonergic (and in MDMA's case noradrenergic and dopaminergic) systems, there is a plausible risk of pharmacokinetic and pharmacodynamic drug‑drug interactions that could alter safety, subjective effects, or therapeutic efficacy. This paper aims to systematically summarise human data on interactions between psychiatric medications and either MDMA or psilocybin. The stated objective was to compile evidence on pharmacokinetic measures (for example plasma drug and metabolite levels), physiological outcomes (for example vital signs, circulating catecholamines), and subjective effects when MDMA or psilocybin are co‑administered with drugs prescribed in psychiatry. The authors emphasise that prior reviews of MDMA interactions were not systematic and that no prior systematic review addressed psilocybin drug‑drug interactions, motivating the present work.

The researchers conducted a systematic review according to PRISMA guidelines and registered the protocol with PROSPERO (CRD42021233519). MEDLINE (via PubMed) was searched for English‑language human studies from 1958 through December 2020. The search strategy comprised 163 Title/Abstract terms: 22 pharmacologic class terms, 135 specific psychiatric medication terms, and six terms to capture MDMA/psilocybin. The PICOS framework specified participants as people exposed to MDMA or psilocybin together with a psychiatric medication; comparisons were typically MDMA or psilocybin with versus without the psychiatric drug; outcomes included pharmacokinetic, physiological and subjective measures; and eligible study designs were broad (RCTs, observational studies, case reports, reviews and meta‑analyses). Screening was performed by two independent reviewers with consensus decisions for disagreements; hand‑searching added 12 articles not retrieved by the database query. Ultimately 40 publications met inclusion: 26 randomized controlled trials (RCTs), 3 epidemiologic studies, and 11 case reports (the latter placed in supplemental materials). The authors standardised reported outcome differences using a percentage‑change formula to compare MDMA/psilocybin plus medication versus MDMA/psilocybin plus placebo. Most RCTs enrolled healthy adult volunteers, used single or short courses of the psychiatric medication (usually acute pretreatment or up to 14 days), had small samples (range 8–23 participants), and applied common exclusions such as pregnancy, age limits, extremes of BMI, psychiatric illness in self or first‑degree relatives, and active substance use. Some trials included pharmacogenetic measures such as CYP2D6 metaboliser status. The review synthesises findings by drug class and by the two index psychedelic drugs, integrating pharmacokinetic, physiological and subjective outcomes reported in the trials and epidemiologic studies.

The systematic search yielded 40 included publications: 26 RCTs, 3 epidemiologic studies (a post‑marketing association analysis, a cross‑sectional survey, and a quantitative analysis of online reports), and 11 case reports. Collective clinical trial enrolment exceeded 200 participants but individual RCTs were small and limited to healthy volunteers. RCTs examined MDMA combinations with SSRIs (citalopram, fluoxetine, paroxetine), SNRIs (duloxetine), NET inhibitors (reboxetine), bupropion, methylphenidate, haloperidol, memantine, and several adrenergic agents (carvedilol, pindolol, clonidine, doxazosin). Psilocybin RCTs studied co‑administration with chlorpromazine, haloperidol, risperidone, buspirone, ergotamine, and one trial with escitalopram. Adrenergic agents with MDMA: Pindolol (20 mg p.o.) given one hour before MDMA (1.6 mg/kg p.o.) reduced a small number of affective subscales and lowered MDMA peak heart rate but did not change mean arterial pressure, temperature, or neurocognitive impairment. Carvedilol (50 mg p.o.) plus MDMA (125 mg p.o.) markedly attenuated cardiostimulant and hyperthermic responses without significantly altering MDMA's subjective effects; circulating epinephrine and norepinephrine paradoxically rose, and MDMA/MDA plasma levels were unchanged. Clonidine (150 µg p.o.) reduced MDMA‑induced increases in circulating norepinephrine and blood pressure, but those reductions mirrored clonidine’s effects alone and did not alter temperature, mydriasis, mood, or adverse effects. Doxazosin (8 mg p.o. ~16 h prior) attenuated mean arterial pressure increases and mood‑heightening ratings yet enhanced tachycardia and circulating norepinephrine. Antipsychotics and other agents with MDMA: Intravenous haloperidol (1.4 mg i.v.) combined with MDMA (1.5 mg/kg p.o.) did not change cardiovascular or thermogenic effects but shifted MDMA’s psychological profile from pleasurable to dysphoric, reducing well‑being and “oceanic boundlessness” and increasing state anxiety. Bupropion XR (titrated to 300 mg) with MDMA (125 mg) moderately reduced norepinephrine and attenuated heart‑rate elevation but prolonged MDMA’s positive mood effects; pharmacokinetic changes included increased MDMA plasma and reduced metabolites (DHMA, HMMA, MDA), consistent with inhibition of CYP2D6 and CYP2B6 and reciprocal increases in bupropion levels. Memantine (20 mg) did not alter MDMA (75 mg) effects on memory or mood. Methylphenidate co‑administration delayed MDMA’s time to maximum concentration without changing MDMA or methylphenidate half‑lives. Serotonin reuptake inhibitors with MDMA: Acute pretreatment with SSRIs (citalopram, fluoxetine, paroxetine) attenuated MDMA’s subjective effects by approximately 30–80% and reduced physiological effects modestly (about 6–14% for most SSRIs; paroxetine showed larger physiological attenuation of ~40–60%). Fluoxetine and paroxetine, strong CYP2D6 inhibitors, increased MDMA plasma concentrations despite the blunted subjective response. The SNRI duloxetine markedly reduced circulating norepinephrine, heart rate, blood pressure, pupillary responses and many subjective measures (well‑being, extroversion, closeness, openness, alterations of consciousness); these reductions occurred despite higher MDMA plasma levels due to CYP2D6 inhibition. Reboxetine (8 mg) reduced norepinephrine, attenuated cardiovascular stimulation and several psychostimulant subjective effects, while not affecting drug “liking”; reboxetine also increased MDMA plasma, consistent with CYP2D6 inhibition. Psilocybin drug‑drug interactions: Antagonism at 5‑HT2A receptors attenuated psilocybin’s subjective and perceptual effects. Chlorpromazine (50 mg p.o.) reduced mydriasis and visual changes induced by psilocybin (0.2 mg/kg). Risperidone (0.5–1 mg p.o.) reduced multiple dimensions of the Altered States of Consciousness scale and lessened psilocybin‑induced reaction‑time delays; haloperidol increased dread of ego dissolution without attenuating perceptual changes. Buspirone (20 mg) reduced “visionary restructuralization” on the 5D‑ASC, while ergotamine (3 mg) had no effect. Escitalopram titrated to 20 mg over 14 days and given 2 hours before psilocybin (25 mg) did not significantly reduce ratings of altered states but did reduce several adverse subjective measures (bad drug effects, fear, anxiety, global adverse effects) and attenuated physiological responses (blood pressure, pupil dilation); escitalopram did not alter psilocin levels or QTc. Epidemiologic and case evidence: A cross‑sectional survey (n=216) of ecstasy users who co‑ingested pharmaceuticals found that 76% of those using antidepressants still reported euphoria but experienced higher rates of adverse effects (for example muscle rigidity, nystagmus, dizziness, headache, profuse sweating). A quantitative analysis of 96 online reports involving psychedelics plus mood stabilisers found two of six lithium‑plus‑psilocybin reports described seizures; lamotrigine reports (n=10) showed no seizures, although the authors judged this evidence low quality due to selection and verification biases. Case reports reviewed in the supplement highlighted severe morbidity and fatalities most commonly when MDMA was combined with MAO inhibitors, with presentations consistent with unrecognised serotonin‑toxicity syndromes.

Sarparast and colleagues interpret the literature as demonstrating clear, clinically relevant interactions between psychiatric medications and MDMA or psilocybin, while emphasising important limitations. The available evidence predominantly concerns MDMA; only a small number of studies addressed psilocybin drug‑drug interactions. Most clinical trials enrolled young, healthy volunteers who received acute or short‑term psychiatric medication exposure rather than chronic treatment, limiting generalisability to typical clinical populations who take medications for months or years. The authors note that some trials used atypical routes or dosing regimens (for example intravenous administration) and imposed exclusion criteria that further constrain extrapolation. Mechanistically, MDMA is susceptible to pharmacokinetic interactions via CYP2D6 (and to a lesser extent CYP2B6, CYP3A4 and others), and many psychiatric medications inhibit CYP2D6; several trials showed increased MDMA plasma concentrations with concomitant CYP2D6 inhibitors. Despite higher MDMA plasma levels, monoamine reuptake inhibitors (SSRIs, SNRIs, NRIs) frequently attenuated MDMA’s subjective and physiological effects, a pattern the authors attribute to pharmacodynamic competition at monoamine transporters preventing MDMA‑induced monoamine efflux. MAO inhibitors were highlighted as a distinct high‑risk class: case reports associate MAOI plus MDMA with severe serotonin toxicity and deaths. Stimulant co‑ingestion may potentiate cardiostimulant and adverse effects, whereas dopamine D2 antagonists altered the subjective profile toward dysphoria without changing cardiovascular measures. For psilocybin, the authors report that 5‑HT2A antagonists consistently attenuate subjective effects, while SERT blockade (escitalopram) did not abolish psychedelic experiences and actually reduced distress and physiological responses, consistent with psilocybin acting primarily via direct serotonin‑receptor agonism and being less dependent on transporter‑mediated increases in synaptic serotonin. The authors acknowledge limitations of the evidence base: small sample sizes, healthy volunteer samples, brief medication exposure, limited studies on benzodiazepines and atypical antipsychotics, sparse data on clinically relevant populations and on chronic medication use, lack of participant diversity reporting, and low‑quality signals from recreational use reports. They call for targeted research to guide clinical decision‑making, including studies of tapering strategies, safety in medically ill populations (for example with hepatic impairment), interactions with commonly used crisis medications such as benzodiazepines or antipsychotics, and investigations that include more diverse samples and account for hormonal influences on metabolism. The authors also highlight pharmacogenetic findings: CYP2D6 poor metaboliser status is associated with higher MDMA exposure and greater physiological and subjective responses, suggesting the value of genotypic or phenotypic considerations in future trials and clinical practice.

This systematic review compiles existing human data on interactions between psychiatric medications and MDMA or psilocybin, finding demonstrable pharmacokinetic and pharmacodynamic interactions that alter physiological and subjective responses. The literature is far richer for MDMA than for psilocybin. Because most controlled studies involved small samples of healthy volunteers with short‑term medication exposure, the findings are not directly applicable to typical clinical populations receiving chronic psychiatric medications. The authors conclude that additional clinical research is needed to inform safe and effective approaches to managing psychiatric medications in the context of MDMA‑assisted or psilocybin‑assisted psychotherapy.