Compared to some of the drugs out there, cannabis can seem relatively harmless. It doesn’t have the ruinous effects of methamphetamines or even substances like synthetic pot. But there has long been suspicion that heavy use might have long-term effects on IQ, for instance [pdf].
Factors that tend to accompany cannabis consumption, such as the use of other drugs and alcohol and, in adolescents, a tendency to skip class, have made it difficult to decisively pin a dip in IQ to marijuana use. To clear away the noise, the authors of a new study in the Proceedings of the National Academy of Sciences turned to the reams of data from the Dunedin Multidisciplinary Health and Development Study, and they’ve found that on average, by the time they reached age 38, heavy pot users diagnosed with cannabis dependence during adolescence suffered an 8-point drop in IQ.
Marijuana, long known as a recreational drug, has earned some respectability with its growing reputation as a pain reliever for those who suffer from cancer, multiple sclerosis, and other ailments. And now, cannabis’s seedy reputation may go entirely to pot: a new strain called Avidekel preserves the drug’s medical properties but does not get users high.
The effects of various breeds of marijuana depend on their balance of the chemicals called cannabinoids. One cannabinoid, called tetrahydrocannabinol or THC, acts on the brain’s cannabinoid receptors to create the sensation of being high. While this feeling is the goal for recreational users, it can be an unwanted side effect for patients who smoke medical marijuana to relieve their pain and then find themselves unable to work, run errands in a car, or function normally until the drug’s effects wear off. The primary reason these users turn to marijuana in the first place is a different cannabinoid, called cannabidiol, which reduces inflammation without any psychoactive side effects.