On the off chance that he is not already a subscriber, I urge Justin Bieber to take a look at the current issue of the New York Review of Books. There, in addition to an article about his fellow musician, Johann Sebastian Bach, is one about marijuana. It was written by the eminent Jerome Groopman of the Harvard Medical School who says, basically, that marijuana is not a benign drug. Smoke it at your own risk.

Justin Bieber in Las Vegas. (Isaac Brekken/Invision via Associated Press) Justin Bieber in Las Vegas. (Isaac Brekken/Invision via Associated Press)

This disquieting news about the weed that for so long has been considered a drug without consequencs is supported by 19 footnotes from such tomes as the Journal of Ethno-pharmacology and comes from a man who has studied marijuana and its effects in his very own laboratory. Citing the scientific literature and with his own findings in mind, Groopman can tell you what you might not want to hear: Richard Nixon may have been right.

Groopman is not arguing that marijuana should not be legalized, which is certainly the trend. He is merely saying, in the customarily cautious way of a cautious scientist, that the drug many of us considered an innocent diversion may be anything but. It is linked to certain kinds of behavior — the DSM has an entry for “cannabis use disorder — and can be particularly pernicious when it comes to young people. It has a big effect on their little brains.

“Several studies demonstrate associations between cannabis and collisions: drivers who use it are estimated to be some two to seven times more likely to be responsible for accidents compared to drivers not using drugs or alcohol.”

Here I turn to the equally eminent Dr. Mitchell S. Rosenthal, the founder of Phoenix House, a substance abuse prevention organization. Rosenthal deals with precisely the people Groopman warns about — people who get into trouble with drugs. That may explain why he is more alarmed than Groopman about the legalization movement. In a Wall Street Journal essay, he unloads on the drug: “Pot damages the heart and lungs, increases the incidence of anxiety, depression and schizophrenia, and it can trigger acute psychotic episodes. Many adults appear to be able to use marijuana with relatively little harm, but the same cannot be said of adolescents, who are about twice as likely as adults to become addicted to marijuana.”

Rosenthal says that marijuana can have a particularly powerful effect on kids — again, because their brains are not yet formed. He worries that legalizing the stuff will widen its popularity and send the message that pot, like milk, is only occasionally bad for you.

I know without checking that I have written columns over the years demanding the legalization of marijuana. I certainly confessed to having “experimented” with the stuff but found it not to my liking. Still, I was of the generation for which it was a rite of passage, apiece with sexual freedom and, much more importantly, civil rights and the anti-war movement. Old fogies warned about pot, J. Edgar Hoover hated it and Richard Nixon made war against — three good reasons right there to have a toke.

But more recently, the news has been grim. I attended a lecture by Eric Kandel, the Columbia University neuropsychiatrist and Nobel laureate, who was surprisingly tough on pot. It had changed, Kandel warned. It was much more powerful that the drug of yesteryear. Kandel knows the brain the way the TV traffic guy knows the roads. Stay away from marijuana, he intoned.

So I say to Mr. Bieber, when a Nobel laureate says stay off the weed, give it some heed. When Groopman and Rosenthal weigh in, pay attention. In the press, your name is associated with marijuana. Your plane got searched for the stuff, you’ve been photographed allegedly smoking it and NBC News says the pilots of your private plane donned masks to avoid inhaling marijuana on a recent flight with you.

Justin, m’boy, you’ve got a habit or maybe just a strong indulgence, but whatever it is, the consequences are plain. Not to put too fine a point on it, you’ve been acting like a jerk. Maybe you ought to lay off the weed. Look at it this way: If it’s legal and everyone’s doing it, then it’s no longer cool. And neither are you.

Richard Cohen writes a weekly political column for The Washington Post.