POLITIFACT

“prime your brain for addiction” has some basis: namely, the results of some studies conducted with rodents.

There are findings to suggest that early exposure to the drug may “sensitize animals to the effects of other drugs,” noted Joshua Isen, an assistant professor at the University of South Alabama, who researches adolescent marijuana use.

For instance, Adams’ office noted that preclinical studies indicate exposure to THC — marijuana’s main psychoactive compound — during a period roughly equivalent to adolescence in rats resulted in greater self-administration of heroin when the animals reach adulthood.

In addition, THC exposure yielded changes in their brains’ reward system — in other words, yes, priming the brain for the rewarding effects of opioids.

But, Isen said, it’s scientifically problematic to draw a line from the effects seen in rodents to what might be happening to a human. Ethical considerations about human research make it more or less impossible to do a randomized controlled trial — the gold standard of scientific research — that would measure how marijuana does or doesn’t affect a still-developing brain.

“We should remain agnostic about the surgeon general’s claim,” Isen argued.

Other experts suggested otherwise, saying that since animal research is the best we can get, it’s worth taking seriously — and it is fairly conclusive.

“What we know is strong enough to say that exposure during adolescence when the brain is developing is a risk,” said Susan Weiss, a scientific adviser to the NIDA director.

But — and this is important context — marijuana is not the only substance that has this potential “priming” for subsequent addiction. The surgeon general’s office acknowledged this finding when we asked follow-up questions. That same context, though, is missing from Adams’ public statement.

“It seems that early exposure to many substances can make it likely someone will be addicted to other substances,” Weiss said.

On a practical level, Isen said, while one could highlight the distinct scientific effect marijuana has, “there is no evidence that marijuana has a uniquely deleterious effect on the developing brain — certainly not more than other substances such as alcohol.”