Ketanserin is a receptor blocker, or antagonist. It sits on the 5-HT2A receptor without activating it, so it can show whether an effect depends on that receptor: if the blocker stops the effect, the receptor is probably required.
That logic has been tested in people with several psychedelics. Ketanserin blocked psilocybin’s effects in a dose-dependent way in a 1998 study (Vollenweider et al., 1998), and fully blocked the general subjective effects of LSD in a 2017 study (Preller et al., 2017). With ayahuasca, a study of 12 volunteers found that ketanserin weakened the brain-wave changes and the intensity of the experience (Valle et al., 2016).
For pure DMT, the decisive blocking test in humans has not been published. A trial registered in Basel gives ketanserin partway through sessions with LSD, psilocybin and DMT, but to standardize how long effects last, not to test whether they need the receptor (ClinicalTrials.gov NCT06899334). In cultured rat neurons, ketanserin abolished the growth of neuron branches promoted by DMT and LSD (Ly et al., 2018), a lab finding that says nothing yet about human brains.
Sources
- Vollenweider et al., NeuroReport, 1998
- Preller et al., Current Biology, 2017
- Valle et al., European Neuropsychopharmacology, 2016
- ClinicalTrials.gov NCT06899334
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