A 2022 review pooled 44 studies of microdosing across nearly seven decades — reporting a spread of effects, widely varying study quality, and the authors' caution that it is too soon to call those effects mostly the placebo effect
A 2022 review gathered together the scientific studies on microdosing psychedelics — taking doses too small to cause a full trip — published from 1955 through 2021, to see what the research as a whole shows.
Microdosing means taking psychedelic doses too small to cause a full trip. This 2022 review pulled together every scientific study the authors could find — 44 in all, published between 1955 and 2021, including little-known work from before these substances were banned — to see what the research so far actually shows. They sorted the reported effects into six areas, from mood and mental health to thinking, personality, and effects on the brain and body. Laboratory studies reported changes in how people perceived pain and time and in brain activity; studies based on people's own reports described changes in thinking and mental health. The studies varied widely in quality, and the authors caution it is premature, and possibly wrong, to say the effects come mostly from expecting to feel better — the placebo effect.
This systematic review synthesised all empirical microdosing research the authors could identify — 44 studies published between 1955 and 2021, including infrequently cited work predating prohibition — and organised reported effects into six categories: mood and mental health; wellbeing and attitude; cognition and creativity; personality; changes in conscious state; and neurobiology and physiology. The included studies showed a wide range in risk of bias depending on design, age, and other characteristics. Laboratory studies reported changes in pain perception, time perception, conscious state, and neurophysiology; self-report studies reported changes in cognitive processing and mental health. The authors examined data on expectation and placebo effects and argue that claims that microdosing's effects are largely due to expectancy are premature and possibly wrong. They also propose suggested dose ranges to address definitional inconsistencies in the literature and offer specific design recommendations for more rigorous future research.
The authors themselves flag several constraints. They report the included studies showed a wide range in risk of bias, depending on design, age, and other study characteristics — so the evidence base is uneven rather than uniformly strong. They note the microdosing literature contains definitional inconsistencies, which they attempt to clarify by proposing dose ranges across substances, and they characterise microdosing as an emerging science, providing specific design suggestions to facilitate more rigorous future research. On the much-discussed question of placebo, they take a deliberately unresolved position: having reviewed expectation and placebo data, they argue it is premature, and possibly wrong, to attribute microdosing's effects largely to expectancy — neither endorsing microdosing's efficacy nor dismissing it as expectation. Design-inherent to the format: as a systematic review this summarises other researchers' studies rather than generating new experimental data of its own, and the authors report those studies ranged widely in risk of bias; it spans nearly seven decades of methods and is not specific to veterans or any clinical population.
This systematic review examined 44 empirical studies of low-dose psychedelics published between 1955 and 2021, summarising reported effects across six categories including mood and mental health and cognition and creativity (Polito & Liknaitzky, 2022).
Read the full paper →