The head-twitch response is a rapid rotational head movement in rodents. Researchers count twitches after a drug as a predictor of hallucinogenic action. A 2009 study found DMT caused head twitches in normal mice but not in mice bred without the 5-HT2A gene (Keiser et al., 2009), and in a 2022 study a 5-HT2A blocker stopped psilocybin-type twitches (Glatfelter et al., 2022).
It is used to screen related compounds. In that 2022 study, only psilocin, psilocybin and psilacetin caused head twitches; baeocystin and aeruginascin did not, even though they bound serotonin receptors in lab assays (Glatfelter et al., 2022). A 2023 paper separated plasticity effects from the twitch: LSD’s head twitch depended on 5-HT2A, while its plasticity effects did not (Moliner et al., 2023).
The marker has limits. A review notes that DMT produces fewer head twitches than most other psychedelics, and none in one mouse strain (Carbonaro and Gatch, 2016). A twitch shows receptor activity in an animal; it cannot show what a person would feel or whether a compound is safe.
Sources
- Keiser et al., 2009, Nature
- Glatfelter et al., 2022, ACS Pharmacology & Translational Science
- Carbonaro and Gatch, 2016, Brain Research Bulletin
- Moliner et al., 2023, Nature Neuroscience
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