Repeated doses of the psychedelic compound 5-MeODMT in rats rapidly produced tolerance to its behavioral effects, with the effective dose doubling and the duration of the syndrome dropping from about 15 minutes to just over 1 minute. This tolerance completely vanished within 4 hours after stopping treatment. The effect was not caused by changes in how much drug entered the brain, but appeared to result from reduced binding of the drug to serotonin receptors. These findings contradict earlier reports that claimed no tolerance develops to 5-MeODMT.
Giving cats ascorbic acid before LSD or apomorphine blocked certain behavioral effects, but it did not block the effects of 5-methoxy-N,N-dimethyltryptamine. These results suggest that the behaviors caused by LSD and apomorphine involve both serotonin and dopamine receptors, and that ascorbic acid can change how LSD acts at dopamine receptors.