Everyone remembers the classic "This is your brain, this is your brain on drugs" ad that scared the living bejesus out of people in the '80s.

At the time, the ad was meant to convey the message that illegal drugs like marijuana hurt the brain. More recent studies, however, have suggested that excessive alcohol use is actually far more harmful to the brain than marijuana use.

According to a recent report from researchers at Wellesley College in Massachusetts, which appeared in the journal Archives of Neurology, there is no longer any doubt that this is the case:

“The take-home message is that, if you want a lot, you’re going to hurt your brain. This is something we knew, but this is a huge study that quantifies that,” said Rajesh Miranda, an associate professor of neuroscience and experimental therapeutics at the Texas A&M Health Science Center College of Medicine.

When it comes to marijuana, the myth that it kills brain cells has largely been dispelled. As the Drug Policy Alliance points out, however:

None of the medical tests currently used to detect brain damage in humans have found harm from marijuana, even from long term high-dose use. An early study reported brain damage in rhesus monkeys after six months exposure to high concentrations of marijuana smoke. In a recent, more carefully conducted study, researchers found no evidence of brain abnormality in monkeys that were forced to inhale the equivalent of four to five marijuana cigarettes every day for a year. The claim that marijuana kills brain cells is based on a speculative report dating back a quarter of a century that has never been supported by any scientific study.

• Heath, R.G., et al. “Cannabis Sativa: Effects on Brain Function and Ultrastructure in Rhesus Monkeys.” Biological Psychiatry 15 (1980): 657-690.

• Ali, S.F., et al. “Chronic Marijuana Smoke Exposure in the Rhesus Monkey IV: Neurochemical Effects and Comparison to Acute and Chronic Exposure to Delta-9-Tetrahydrocannabinol (THC) in Rats.” Pharmacology Biochemistry and Behavior 40 (1991): 677-82.