I've heard countless times that "Cannabis doesn't really get me high anymore. I just use it to feel normal." For years, I thought the answer was straightforward: tolerance to the drug. That's also true—but it is an incomplete answer.

A fascinating new study by Katharina Lege and colleagues at Maastricht University will be published on July 15th. It suggests something else may be happening. Tolerance does not mean the brain has recovered. It means the brain has adapted to cannabis.