Estimating Cardiac 5-HT2B Safety Margins for Repeated Low-Dose Psilocybin Using an Exposure–Response Model
William J. Tyler, E. Sellers, Michael B. McDonnell
bioRxiv July 23, 2026 preprint DOI: 10.64898/2026.07.19.739440 (opens in new tab)
Study at a glance
AI-extracted from the abstract| Characteristics | Modeling study with animal validation |
|---|---|
| Population | Rats (for histopathology); otherwise modeled exposures |
| Interventions | Psilocybin Psilocin |
| Dose | 3 mg daily psilocybin (candidate regimen); continuous psilocin in rats |
| Duration | 12 days (rat exposure) |
| Topics | Psilocybin Serotonin |
| Key points | A 3 mg daily psilocybin regimen yields a 5-HT2B signaling increment of +3 %·h/day, roughly two orders of magnitude below the weakest valvulopathic exposure (+172 %·h/day). Rats receiving continuous psilocin for 12 days showed no valvular lesions, suggesting a favorable safety margin, though longer-term fibrosis cannot be excluded. |
Abstract
Repeated low-dose psilocybin is being developed as a scalable outpatient treatment for mood and anxiety disorders, but chronic exposure raises concern because psilocin binds the cardiac serotonin 5-HT2B receptor, whose sustained agonism causes drug-induced valvular heart disease (VHD). We evaluated this risk using an exposure–response model that incorporates functional efficacy and exposure duration rather than binding affinity alone. Plasma psilocin concentrations were converted into the time-integrated increment in 5-HT2B Gq signaling above endogenous serotonergic tone (ΔTIA) and calibrated against drugs and conditions with known valvular outcomes. All modeled exposures known to cause human VHD scored ΔTIA ≥ +172 %·h/day, whereas exposures not associated with VHD scored ≤ +28. A candidate 3 mg daily psilocybin regimen scored ΔTIA +3, roughly two orders of magnitude below the weakest valvulopathic exposure. This safety margin arises from psilocin’s low-efficacy partial agonism at 5-HT2B (Emax ≈51.8% of serotonin, compared with 96% for norfenfluramine) and its short half-life (≈ 2.5 h), which prevents accumulation and produces brief daily receptor engagement. In support of the model, rats receiving continuous psilocin for 12 days at plasma concentrations ≈2.4-fold above the projected human peak for 3 mg daily psilocybin showed no valvular lesions by blinded histopathology. This exposure duration however cannot exclude slowly developing fibrosis. Emerging human data, including serial echocardiography in repeated LSD microdosing and a large observational cohort, are also agreement with the model. Collectively, these findings suggest a favorable safety margin for daily, sub-hallucinogenic psilocybin use in clinical indications. Nevertheless, continued pharmacological and clinical investigations should include prospective echocardiographic monitoring to advance the clinical safety profile of sub-hallucinogenic psilocybin and support its evaluation across a broad array of therapeutic programs. Graphical Abstract Three key determinants of cardiac safety margins for repeated low-dose psilocybin are shown. Psilocin is a low-efficacy partial agonist at 5-HT2B (ceiling ≈52% vs 96% for norfenfluramine; left). Its short half-life yields a brief daily pulse of receptor engagement rather than a sustained plateau (center). The resulting integrated 5-HT2B signal (ΔTIA) at 3 mg daily lies roughly two orders of magnitude below valvulopathic exposures, and continuous in vivo exposure produced no valvulopathy (right).
Comparable studies
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| Study | Year | Design | Participants |
|---|---|---|---|
| Psilocybin induces rapid and persistent growth of dendritic spines in frontal cortex in vivo Mice | 2021 | Observational cohort | |
| Neurotoxicity of the psychedelic amphetamine, methylenedioxymethamphetamine. Rats (implied by typical neurochemical study context) | 1987 | Experimental study | |
| Psychedelics promote neuroplasticity through the activation of intracellular 5-HT2A receptors In vitro and in vivo (rodent) models | 2023 | Experimental study | |
| 3,4-Methylenedioxymethamphetamine and 3,4-methylenedioxyamphetamine destroy serotonin terminals in rat brain: quantification of neurodegeneration by measurement of [3H]paroxetine-labeled serotonin uptake sites. Rat brain | 1987 | Animal experiment | |
| Comparison of the monoamine transporters from human and mouse in their sensitivities to psychostimulant drugs Human and mouse dopamine, norepinephrine, and serotonin transporters expressed in cells | 2006 | In vitro laboratory study |