The study compares altered states of consciousness induced by the hallucinogens (-)Delta9-trans-Tetrahydrocannabinol (Delta9-THC) and N,NDimethyltryptamine (DMT) using two placebo control groups. A total of 24 subjects received 250 microg Delta9-THC p.o./kg body weight and 26 subjects were treated with 250 microg DMT i.m./kg. Placebo was given to 24 subjects. The effects were assessed by a questionnaire administered following the experimental conditions. Questionnaire items were combined into the following eight scales according to their content and several criteria of the theory of mental testing: visual hallucinations (illusions), auditory hallucinations (illusions), impairment of memory and attention, depersonalization syndrome, derealization syndrome, changes of body image, euphoric state and anxious depressive state.