Marijuana and the Developing Brain
Weir (2015) Monitor on Psychology
There are a lot of open questions" about the long-term effects of marijuana, says Susan Weiss, PhD, director of the division of extramural research at the National Institute on Drug Abuse (NIDA). "But there's a growing literature, and it's all pointing in the same direction: Starting young and using frequently may disrupt brain development.
Marijuana shows considerable promise for treating medical conditions including pain, muscle spasms, seizure disorders and nausea from cancer chemotherapy. At least some of those benefits are thought to come from cannabidiol, a chemical component of the marijuana plant not thought to produce mind-altering effects. But there's a lot left to learn about this and other chemical compounds in marijuana. Recently, the Senate recommended $800,000 for an Institute of Medicine study on medical marijuana, and has also encouraged the National Institutes of Health to support more research on cannabidiol.
What's clear, however, is that marijuana's signature high comes from a psychoactive component known as tetrahydrocannabinol (THC). And evidence is mounting, says Weiss, that THC is not risk-free.
In the short term, marijuana use has been shown to impair functions such as attention, memory, learning and decision-making. Those effects can last for days after the high wears off. Heavy marijuana use in adolescence or early adulthood has been associated with a dismal set of life outcomes including poor school performance, higher dropout rates, increased welfare dependence, greater unemployment and lower life satisfaction.