Where the term comes from

In drug development, a microdose is a tiny test dose used to study how the body handles a new compound. In the psychedelic sense, the term is closely tied to the researcher James Fadiman, whose 2011 book The Psychedelic Explorer’s Guide many people treat as a protocol. The word is now also used for low doses of weight-loss drugs, a separate topic.

What placebo-controlled studies found

In the largest placebo-controlled study, 191 people who microdosed with their own psilocybin or LSD mixed their doses with empty capsules in coded envelopes for four weeks. Well-being and other measures improved, but they improved in the placebo group too, with no significant difference between groups, and participants guessed correctly whether a capsule was active 72 percent of the time. In a six-week trial with 80 healthy men, 14 small doses of LSD raised ratings such as happiness and energy on dosing days, but no questionnaire or thinking test changed from start to finish; four men taking LSD withdrew because of anxiety. In a 2025 trial in 53 adults with ADHD, symptoms improved in both groups, with no advantage for LSD.

A 2024 review of 19 placebo-controlled studies argued it is still too early to call microdosing a placebo: the studies were small, short and mostly in healthy volunteers.

Risks and unknowns

Long-term safety is largely unstudied. Psilocybin and LSD also act on the 5-HT2B receptor, which has been linked to heart valve disease, and a 2023 analysis judged valve damage a potential risk of long-term microdosing that had not been properly tested. Products add their own risk: in 2024 the FDA tied “microdosing” chocolates and gummies from one brand to 180 illnesses, 73 hospitalizations and three possible deaths, and its tests found a mix of compounds, including a prescription drug, that varied even within one flavor. The 5-HT2B section of our safety and screening page covers why repeated, self-directed dosing carries different risks from a few supervised sessions.

Related terms

Psilocybin: the compound most often microdosed, and what trials of full doses show.

Psychedelic Harm Reduction: ways to lower the risks of use outside clinical settings.

Psilocybin Contraindications: medical reasons some people should not take psilocybin.