In 2004, a team of pharmacologists at the University of Michigan Medical School, led by William Fantegrossi, set out to test the addiction potential of psilocybin — a hallucinogenic compound derived from certain mushrooms — on a cohort of rhesus monkeys. The researchers presented one group of primates with a lever that, when pressed, injected them with a dose of the compound. A second group was hooked up to levers that injected mere saline solution.
In similar experiments, monkeys have been known to repeatedly press levers that inject the drugs heroin, cocaine and even methylenedioxymethamphetamine (MDMA). It’s a phenomenon that researchers attribute to the “reinforcing effects” of these drugs. But when it came to psilocybin, the results were erratic. Some repeatedly pressed the lever to the point of intoxication; others swore off the lever for good after one dose. On average, the monkeys were no more prone to self-administering psilocybin than the less exciting saline solution.
During the last two decades, scientists have reopened a line of inquiry into the therapeutic applications of psychedelic compounds that was abruptly closed after the drugs were first outlawed in the 1960s. But the rhesus monkey study is one of many pieces of evidence for something that researchers have long suspected: Unlike other widely used recreational drugs, certain psychedelics aren't reliably addictive.
