The Stamets stack: where it came from and what studies found

The Stamets stack, in short

The Stamets stack is psilocybin combined with lion's mane mushroom (Hericium erinaceus) and niacin (vitamin B3), proposed by Paul Stamets, whose company Fungi Perfecti is based in Olympia, Washington.⁶ He filed a provisional patent application on it in July 2016, and three US patents on versions of it were granted in 2022 and 2023.¹² As of November 2, 2026, we found no published placebo-controlled trial of the combination, and blinded trials of psilocybin microdosing have found little or no benefit over placebo.⁹¹²

The team behind this almanac also sells psilocybin microdose capsules through an online shop for adults 21+; mail order is illegal under federal law and in every state.³

A Washington idea: Stamets, Olympia and the patents

Stamets owns Fungi Perfecti, an Olympia company that sells lion's mane supplements, and he's the named inventor on the stack's patent family.⁶¹ After a provisional filing in July 2016, application 15/494,503 was filed on April 23, 2017, and published on January 25, 2018, as US 2018/0021326 A1. A final rejection followed in January 2019, and the application was listed as abandoned on September 12, 2019, for failure to respond; a continuation filed in December 2018 went forward. In 2021 Stamets assigned the application and its successors to Turtle Bear Holdings LLC, a Washington company.¹²

Three patents titled "Psilocybin compositions" followed:²

• US 11,471,450 B2, October 18, 2022: psilocybin or psilocin with lion's mane extract and an Inonotus mushroom; further claims add niacin.
• US 11,590,120 B2, February 28, 2023: psilocybin or psilocin with lion's mane extract; other claims add niacin, and one pairs psilocybin or psilocin with niacin alone.
• US 11,701,348 B1, July 18, 2023: a method of reducing symptoms of depression by giving psilocybin or psilocin, lion's mane extract and niacin together; other claims cover psilocybin or psilocin with just one of the two.

A patent isn't evidence that an invention works.

In April 2017 Stamets gave an invited talk at Psychedelic Science 2017 in Oakland, California (the conference ran April 19 to 24).⁴⁵ A 2021 paper he co-authored cites the Oakland talk for the idea that niacin's flushing might "facilitate psilocybin bioavailability", and says stacking's popularity likely comes from anecdotal reports "rather than from a strong empirical basis."⁵ A 1955 study cuts the other way: niacin delayed or blunted the effects of LSD.¹⁶

The Microdose.me studies

The human data we found on the stack come from Microdose.me, an app study run by University of British Columbia researchers with Quantified Citizen, a Vancouver company, and Stamets as co-author.⁵

In the 2021 sample, 39% of microdosers reported adding lion's mane, 18% niacin and 16% both; stackers and non-stackers had similar depression, anxiety and stress scores.⁵ In 2022, adding lion's mane and niacin didn't change mood or mental health results. Among microdosers aged 55 and over, the three-part combination was linked to greater improvement on a finger-tapping test over the month than psilocybin alone or with lion's mane. The authors chose 55 "as a convenience based on power", called the finding "suggestive" and wrote that "replication is required".⁶

The three papers are observational, with no placebo, no random assignment and no check on what anyone took; the first two describe self-selected users of Apple devices, recruited through psychedelic media, such as podcasts, and talks at psychedelic conferences. The papers declare commercial ties. Stamets invested in Quantified Citizen and MycoMedica Life Sciences and applied for patents on the combination; Quantified Citizen's co-founders are co-authors; and the 2025 lead author's fellowship was in partnership with MycoMedica, which Stamets co-founded.⁵⁶⁷

What placebo-controlled trials and reviews found

We found no placebo-controlled trial of the three-part stack in PubMed or ClinicalTrials.gov on November 2, 2026. Blinded trials of microdosing itself point away from the app results:

• In a 2021 "self-blinding" study, people took placebos, microdoses or a mix at home without knowing which; 191 of 240 starters finished, and about a quarter of starters used psilocybin mushrooms, the rest mainly LSD. The placebo and microdose groups both improved over four weeks with no significant difference, and the authors concluded the "anecdotal benefits of microdosing can be explained by the placebo effect."⁸
• Two double-blind Leiden trials of psilocybin truffles, published online in 2025, found no significant effect on behavioral or subjective measures compared with placebo, while "negative bodily feelings" rose on the active substance.⁹
• A 2026 systematic review of 24 studies (3,681 participants), six of them pooled in meta-analyses, found no "consistent immediate benefits" for depression, anxiety or stress in healthy adults.¹² A meta-analysis of 14 studies of thinking skills (1,614 participants), published online in November 2025, found "a significant decrease in cognitive control" and no detectable effect on other cognitive domains.¹³

A 2024 review argued "it is not yet possible to determine whether microdosing is a placebo", citing a small number of controlled studies, small samples and only a few doses tested in each; one of its authors co-wrote the 2021 Microdose.me paper.¹⁴ See the research register for Washington studies.

Why expectancy matters

Expectancy, what people believe a treatment will do, shapes what they report. In a four-week online study from Imperial College London that 81 microdosers completed, positive expectations at the start predicted later gains in wellbeing, "suggestive of a significant placebo response."¹⁰ In the self-blinding study, small differences on microdosing days "can be explained by participants breaking blind", that is, guessing they'd had the real thing.⁸ The 2022 Microdose.me authors acknowledge possible bias from recruiting "through venues that are favorable toward psychedelic use".⁶ That's why blinded trials carry more weight.

Safety and who should avoid it

We found no study of the stack's long-term safety. On psilocybin:

• Heart valves, a theoretical risk. Psilocin activates the 5-HT2B receptor, whose repeated activation is blamed for heart-valve damage from fen-phen and the migraine drug methysergide. Whether repeated low doses of psilocybin do the same "remains to be seen"; preclinical tests had shown no signal as of 2019.¹⁵
• Lithium. Of 62 online reports of lithium taken with a psychedelic, 47% described seizures, against none of 34 with lamotrigine.¹¹
• MAOIs and antidepressants. A 2024 review of 52 human studies found other drugs "both attenuated and potentiated" psychedelic effects; with psilocybin, the antidepressant escitalopram reduced anxiety but not positive mood. It included no human study of psilocybin with an MAOI antidepressant (its MAOI data came from LSD and DMT).¹⁶ Ask a prescriber or pharmacist.
• Psychosis. Modern psychedelic therapy trials "exclude participants with psychotic spectrum illnesses" because psychedelics can worsen them.¹⁵

Help: call 911 in an emergency. Call or text 988 for crisis support. Poison Control, 1-800-222-1222, reaches the Washington Poison Center from Washington. Fireside Project peer support: call or text 62-FIRESIDE (623-473-7433), 11 a.m. to 11 p.m. Pacific daily, as of November 2, 2026.

The law in Washington

Washington has no microdosing exception. Psilocybin and psilocyn are Schedule I under RCW 69.50.204, and RCW 69.50.4013 makes knowingly possessing a controlled substance without a prescription a gross misdemeanor, punishable by up to 180 days in jail (up to 364 days for someone with two or more such convictions after July 1, 2023); prosecutors are encouraged to divert such cases. The section's amount-based exceptions apply to cannabis, not psilocybin.³

Neither lion's mane nor niacin is on Washington's five drug schedules;³ niacin is sold in multivitamins and B-complex supplements,¹⁷ and lion's mane is sold as a supplement, including by Fungi Perfecti.⁶ For Seattle's enforcement history, see the history entry and timeline.

Timeline of the stack