Tolerance of the behavioral effects of the short-acting, endogenous hallucinogen,
N,N-dimethyltryptamine (DMT) is seen inconsistently in animals, and has not been produced
in humans. The nature and time course of responses to repetitive, closely spaced administrations
of an hallucinogenic dose of DMT were characterized. Thirteen experienced hallucinogen
users received intravenous 0.3 mg/kg DMT fumarate, or saline placebo, four times,
at 30 min intervals, on 2 separate days, in a randomized, double-blind, design. Tolerance
to "psychedelic" subjective effects did not occur according to either clinical interview
or Hallucinogen Rating Scale scores. Adrenocorticotropic hormone (ACTH), prolactin,
cortisol, and heart rate responses decreased with repeated DMT administration, although
blood pressure did not. These data demonstrate the unique properties of DMT relative
to other hallucinogens and underscore the differential regulation of the multiple
processes mediating the effects of DMT.