The largest placebo-controlled microdosing study found the benefits were real — but the placebo produced them too
A 2021 citizen-science study followed adults who were already microdosing psychedelics on their own and had them secretly test their real doses against identical dummy capsules.
Many people who microdose psychedelics say it lifts their mood and well-being, but those reports could be a placebo effect. In this study, 191 adults who already microdosed used online instructions to hide their own doses and identical blank capsules under scan-only codes, so they couldn't tell which they were taking. Over four weeks, their mood and well-being scores improved — but they improved just as much when people were unknowingly taking blanks, and there was no real difference between the two. The researchers concluded the benefits are genuine, but appear driven by expectation rather than the drug itself.
This self-blinding, placebo-controlled citizen-science study (191 completers, from 1630 sign-ups and 240 starters) had experienced microdosers implement placebo control and randomization at home: active doses and identical-looking placebos were concealed in opaque capsules tagged with non-human-readable QR codes. Participants were allocated to a placebo group (four weeks placebo), a half-half group (two weeks each), or a microdose group (four weeks microdosing). All psychological outcomes improved significantly from baseline in the microdose group, but the placebo group also improved, and planned comparisons revealed no significant between-group differences at either the week-5 or week-9 follow-up. The authors describe it as the largest placebo-controlled psychedelic trial to date.
The study's strengths are its scale and its placebo control, both rare in microdosing research. Its limits are stated plainly by the authors: they could not verify the nature, purity, or dosage of the substances participants used, because people microdosed with their own supply; they could not confirm whether participants followed the self-blinding procedure accurately; and they note they cannot rule out that a study in a clinical population would yield more promising results. By design this is a part-controlled, part-observational study — the authors judge it superior to conventional observational data but inferior to a controlled clinical trial. Participants were self-selected adults already microdosing, not a clinical or veteran sample.
Szigeti et al. describe their study as the largest placebo-controlled trial on psychedelics to date (Szigeti et al., 2021).
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