A systematic review and interviews with ceremony participants assessed the acute toxicity and psychological risks of ayahuasca, a brew containing dimethyltryptamine (DMT) and β‐carbolines used in religious ceremonies. No animal models tested ayahuasca's acute toxicity or abuse potential, but separate studies of DMT and harmala alkaloids suggest a lethal human dose is probably over 20 times a typical ceremonial dose. Adverse effects may occur with casual use, especially alongside serotonergic substances. DMT can cause aversive reactions or transient psychotic episodes that resolve within hours. There is no evidence of substantial abuse potential, and long-term psychological benefits are documented when used in a well-established social context. The safety margin is comparable to codeine, mescaline, or methadone.
A review of 20 abused psychoactive substances compared their dependence potential and acute toxicity. The margin of safety, or therapeutic index, varied dramatically across substances. Intravenous heroin had the greatest risk of dependence and acute lethality, while oral psilocybin had the least. The assessment did not include hazards from behavioral deficits, perceptual distortion, or chronic illness.
A graduate student's ingestion of psilocybin (magic mushrooms) produced an altered state of consciousness, which he later reported to psychologists Fred Skinner and Abraham Maslow 30 years ago, noting their reactions. The author suggests that familiarity with hallucinogens can improve communication with terminally ill people and that these substances may help realize visionary potential.