Pot impairs learning in adolescent rats: study

Another reason for people not to smoke pot

The main active ingredient in marijuana leads to short-term impairment of learning in adolescent rats, but doesn't seem to affect adults similarly, Duke University Medical Center researchers report.

Their study compared the effects of delta9-tetrahydrocannabinol (THC) on the memory ability of adolescent and adult rats to see if the animals, and perhaps humans, are more sensitive to THC at certain stages. Researchers found that chronic exposure to THC during adolescence may not lead to long-term damage persisting into adulthood, but said the finding should be interpreted cautiously, since other studies have suggested the damage may be longer lasting.

The study tested the effects of THC exposure on memory and learning by dosing rats with varying amounts, training them to navigate a "water maze," and then measuring how well the rats remembered how to get to a stationary platform in the water. After the THC had cleared the rats' systems and the adolescents had reached full maturity, the researchers tested how well they performed in the water maze. The chronic exposure appeared to have no effect on the rats' later learning abilities, the study found.

The findings appear in the March 2006 issue of the journal Pharmacology, Biochemistry and Behavior, which is expected to be published June 8.

"There are plenty of good reasons for adolescents to not smoke pot," said H. Scott Swartzwelder, a professor of psychiatry at Duke and the Durham Veterans Affairs Medical Center and the senior author on the study. "The teen years require a lot of learning and preparation for adulthood."

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