In an observational study, researchers measure people as they are, rather than deciding who gets what. Surveys, cohort studies, chart reviews and cross-sectional studies are all observational. They can study large groups and rare outcomes cheaply, which trials often can’t.
Their limits show in psychedelic research. A study of 1,435 microdosers found higher self-ratings on microdosing days than on other days, and its authors cautioned that the design was observational (St Pierre et al., 2026). A hospital chart review linked same-time cannabis use with higher odds of psychiatric admission after mushrooms, but with a very wide confidence interval (Bhatt et al., 2026).
The core problem is confounding: people who choose to use a substance differ in many ways from those who don’t. Observational findings point to questions; randomized controlled trials are designed to answer them. One microdosing survey was later corrected, a reminder to check for corrections (Rootman et al., 2022, author correction).
Sources
- St Pierre et al., Psychopharmacology, 2026
- Bhatt et al., 2026
- Author correction to Rootman et al., 2022
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