Psilocybin - Toxicity and Harm Potential

Toxicity and Harm Potential

The toxicity of psilocybin is low. In rats, the median lethal dose (LD₅₀) when administered orally is 280 milligrams per kilogram (mg/kg), approximately one and a half times that of caffeine. When administered intravenously in rabbits, psilocybin's LD₅₀ is approximately 12.5 mg/kg. Psilocybin comprises approximately 1% of the weight of Psilocybe cubensis mushrooms, and so nearly 1.7 kilograms (3.7 lb) of dried mushrooms, or 17 kilograms (37 lb) of fresh mushrooms, would be required for a 60-kilogram (130 lb) person to reach the 280 mg/kg LD₅₀ value of rats. Based on the results of animal studies, the lethal dose of psilocybin has been extrapolated to be 6 grams, 1000 times greater than the effective dose of 6 milligrams. The Registry of Toxic Effects of Chemical Substances assigns psilocybin a relatively high therapeutic index of 641 (higher values correspond to a better safety profile); for comparison, the therapeutic indices of aspirin and nicotine are 199 and 21, respectively. The lethal dose from psilocybin toxicity alone is unknown at recreational or medicinal levels, and has rarely been documented—as of 2011, only two cases attributed to overdosing on hallucinogenic mushrooms (without concurrent use of other drugs) have been reported in the scientific literature. Most of the comparatively few fatal incidents reported in the literature that are associated with psychedelic mushroom usage involve the simultaneous use of other drugs, especially alcohol. Probably the most common cause of hospital admissions resulting from magic mushroom usage involve "bad trips" or panic reactions, in which affected individuals become extremely anxious, confused, agitated, or disoriented. Accidents, self-injury, or suicide attempts can result from serious cases of acute psychotic episodes.

Repeated use of psilocybin does not lead to physical dependence. A 2008 study concluded that, based on US data from the period 2000–2002, adolescent-onset (defined here as ages 11–17) usage of hallucinogenic drugs (including psilocybin) did not increase the risk of drug dependence in adulthood; this was in contrast to adolescent usage of cannabis, cocaine, inhalants, anxiolytic medicines, and stimulants, all of which were associated with "an excess risk of developing clinical features associated with drug dependence". Similarly, a 2010 Dutch study ranked the relative harm of psilocybin mushrooms compared to a selection of 19 recreational drugs, including alcohol, cannabis, cocaine, ecstasy, heroin, and tobacco. Magic mushrooms were ranked as the illicit drug with the lowest harm, corroborating conclusions reached earlier by expert groups in the United Kingdom. Although no studies have linked psilocybin with birth defects, it is recommended that pregnant women avoid its usage.