Psychedelic medicine: The biology underlying the persisting psychedelic effects

Psychedelics such as psilocybin, ayahuasca and LSD have re-emerged as potential therapeutic agents for severe stress-related disorders, including treatment-resistant depression. Kuypers summarises preliminary clinical findings showing sustained symptom improvement after very limited dosing—acute improvement up to seven days after a single ayahuasca dose and symptom reductions lasting up to six months after two psilocybin sessions—and notes survey and naturalistic reports of lasting reductions in stress and depressive affect. The paper also highlights the growing interest in micro-dosing, the repeated use of sub-perceptual doses (often around one-tenth of a full dose), which users anecdotally report improves concentration, creativity and ADHD symptoms despite producing no overt psychedelic experience. This paper sets out to propose mechanistic hypotheses for the persisting psychological effects of both regular and low (micro-)doses of psychedelics. Rather than present new empirical data, Kuypers integrates prior findings and argues for a central role of sleep processes in the lasting effects of regular doses and for an indirect, gut-mediated route—via the microbiome and related metabolic pathways—for low doses. The author frames these as testable hypotheses and outlines experimental approaches to evaluate them, while acknowledging that multiple interacting biological systems are likely involved but are not the focus here.

This is a theoretical, hypothesis-driven paper rather than an original empirical study. Kuypers conducts a narrative synthesis of existing preclinical and clinical literature on psychedelics, sleep, the gut-brain axis and related biological systems, and from that synthesis proposes mechanistic models linking dose-dependent psychedelic effects to sleep and the microbiome. Rather than following systematic review methods, the paper draws selectively on human clinical reports, EEG sleep studies, animal models, pharmacological evidence about serotonin (5-HT) 2A receptor actions, and microbiome research to generate hypotheses. The author describes specific experimental designs that could test these hypotheses: placebo-controlled human trials manipulating sleep (for example, sleep restriction after psychedelic administration) with EEG assessment of sleep architecture and measures of mood and cognition; pharmacological blockade designs combining psychedelics with a 5-HT2A/C antagonist (ketanserin) to probe receptor involvement; and preclinical and clinical studies of psychedelic effects on the gut microbiome including metabolome measures such as tryptophan and kynurenine pathway metabolites. Proposed animal studies would examine whether psychedelics alter microbiome composition and whether effects differ between natural (plant-derived) and synthetic compounds. Clinical studies would add psychological outcome measures to test whether any microbiome or metabolome changes correlate with mood and higher-order cognitive-emotional processes. The paper emphasises use of placebo control and recommends inclusion of biomarkers sensitive to diet–microbiome interactions when testing these pathways.

The paper does not present new experimental results; instead it summarises prior empirical findings that motivate the hypotheses. Key points drawn from the literature include: evidence of sustained antidepressant effects after limited psychedelic exposure (single-dose ayahuasca effects reported up to seven days; two psilocybin sessions associated with improvements up to six months), and naturalistic reports of decreased stress and depressive affect lasting up to four weeks after psychedelic sessions. Kuypers highlights high prevalence of sleep disturbances in depression—more than 80% of patients report poor sleep—and notes links between poor sleep, altered functional connectivity in prefrontal and limbic regions, and emotional dysregulation. Two EEG sleep studies are cited as reporting that psychedelics (ayahuasca and LSD) alter sleep architecture, including effects on REM sleep and enhancement of non-REM stages. Preclinical work showing that a ketamine dose downregulates clock genes is presented alongside clinical observations that sleep deprivation can transiently relieve depressive symptoms, supporting a role for circadian mechanisms in rapid antidepressant responses. Regarding micro-dosing and the gut, the author collates evidence that the gut–brain axis—including the enteric nervous system, autonomic branches, neuroendocrine and neuro-immune components and the gut microbiome—modulates CNS function. An animal study is noted in which transplantation of microbiota from depressed humans into germ-free rats produced depression-like behaviours. Dietary manipulations, including tryptophan supplementation, are reported to shift microbiome composition in ways associated with intestinal homeostasis. Kuypers emphasises that approximately 95% of serotonin is located in the gastrointestinal tract and that serotonergic drugs affect both CNS and GI function; ayahuasca is noted to induce GI symptoms such as nausea and vomiting. The kynurenine pathway, the principal route of tryptophan metabolism, is described as a plausible mediator between peripheral changes and central effects, with metabolites (kynurenine and kynurenic acid) having differing central nervous system bioavailability and actions. Finally, anecdotal and survey reports are used to note that micro-doses, despite being sub-perceptual, are attributed by users to positive cognitive and mood effects, prompting the microbiome-based indirect mechanism hypothesis. Where numerical details are available in the extracted text, Kuypers cites the >80% prevalence of sleep complaints in depression, the 95% localisation of serotonin to the gut, and that four major bacterial phyla (Firmicutes, Bacteroidetes, Proteobacteria, Actinobacteria) account for roughly 98% of gut bacteria. The paper uses these prior findings to motivate specific empirical tests rather than to provide new quantitative estimates.

Kuypers interprets the assembled evidence as supportive of two complementary hypotheses: that a regular (perceptual) psychedelic dose may exert persisting psychological effects in part by resetting or modulating sleep and circadian processes, and that low, sub-perceptual micro-doses may produce lasting effects indirectly via alterations in the gut microbiome and related metabolic pathways. The author emphasises that these are proposed central roles and that other biological systems (immune, neuroendocrine, large-scale brain networks and neuroplasticity) likely interact with sleep and the gut, but those interactions are outside the present paper's scope. The paper recommends a programme of placebo-controlled experimental studies to test these mechanisms, including sleep-manipulation paradigms with EEG, pharmacological blockade of 5-HT2A/C receptors to probe receptor-specific effects, and microbiome-focused preclinical and clinical studies incorporating metabolomic biomarkers such as tryptophan and kynurenine metabolites. Kuypers suggests testing whether natural versus synthetic forms and different routes of administration produce distinct biological effects, given that orally administered phytochemicals transit the gut and may exert peripheral actions absent with non-oral or non-plant forms. Limitations and potential confounders are explicitly acknowledged. Dietary changes and broader lifestyle modifications that commonly accompany psychedelic sessions could independently alter the microbiome and contribute to reported mood benefits. The author also notes that different forms of the same compound (for example, whole mushrooms versus synthetic psilocybin) may contain additional nutritional constituents that affect the gut. These factors complicate attribution of persisting effects solely to the pharmacology of the psychedelic and argue for careful experimental control of diet, administration route and form in future studies. Finally, Kuypers stresses the need for a holistic research approach that integrates sleep, the microbiome and other biological systems rather than focusing on any single pathway in isolation.

Kuypers concludes that modification of sleep and the gut microbiome may represent additional or alternative biological routes by which serotonergic psychedelics produce persisting effects on mood and well‑being. The paper calls for psychedelic research to ‘zoom out’ and incorporate the sleep and gut–brain axes, and to examine substance-related factors such as route of administration and form as well as participant factors like diet and lifestyle when studying enduring psychological outcomes.