PET imaging uses a small amount of a radioactive tracer that binds to a chosen target. The scanner detects where the tracer collects, giving a map of that target. Psychedelic research uses it to map receptors, measure how many are occupied by a drug, and estimate synapse density.
A 2019 PET study of eight healthy volunteers found that how intense people rated a psilocybin experience tracked how many 5-HT2A receptors psilocin occupied and how much psilocin was in the blood (Madsen et al., 2019). A 2026 study used PET of SV2A, a protein found at synapses, in fifteen healthy volunteers, and found no statistically significant overall rise in synapse density a week after a single dose (Johansen et al., 2026).
PET is slow and expensive, involves radiation, and is usually done with small groups. Average PET maps of 5-HT2A receptor density have also been compared with fMRI results from DMT sessions (Timmermann et al., 2023). With so few people per study, PET findings in psychedelic research are best read as early, not settled.
Sources
- Madsen et al., Neuropsychopharmacology, 2019
- Johansen et al., Translational Psychiatry, 2026
- Timmermann et al., PNAS, 2023
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