Talk to your grandparents about marijuana - before somebody else does.

The latest release of a massive federal drug use survey shows monthly marijuana use has skyrocketed among older Americans. The past decade, in fact, has seen a sea change in the demographics of marijuana use: As recently as the early 2000s, teens were more than four times more likely to use marijuana than 50 and 60 somethings. But as of 2017, Americans age 55 to 64 are now slightly more likely to smoke pot on a monthly basis than teens age 12 to 17. That difference is within the survey's margin of error.

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The oldest age group - seniors age 65 and older - has seen steep increases in marijuana use as well. In the mid-2000s monthly marijuana use among this group was effectively at zero percent. As of last year 2.4 percent of seniors used marijuana monthly, and nearly 4 percent were using on at least an annual basis.

Federal data showed that marijuana use among middle-aged Americans surpassed teen use several years ago, which underscores a point that often gets lost in contemporary debate about marijuana legalization: while debates about marijuana use tend to focus on the drug's effects on young people, marijuana use is becoming more concentrated among older Americans. The effects of long-term marijuana use among that cohort are less understood.

There are a number of factors driving these trends. Nine states plus the District of Columbia have legalized marijuana for adult recreational use since 2012. It's only natural that those laws would boost use among older Americans while having little effect among younger ones.

The legalization wave happens to be happening as baby boomers are entering their golden years. The boomers were big supporters (and users of) pot in the late 60s and 70s, and it seems that many of them are using their retirement years to revisit some of the mind-altering experiences of their youth.

Finally, medical concerns appear to be a key factor driving marijuana use among older Americans. A recent study conducted by Benjamin Han and Joseph Palamar of New York University found that more than 20 percent of marijuana users over age 65 said a doctor recommended they try the drug. Other research has shown that marijuana is particularly effective at treating chronic pain, which is particularly prevalent among the elderly. Several recent studies have found that Medicare prescriptions for opiate painkillers are lower in states with medical marijuana programs.

On net, grandparents smoking state-legal weed in their homes is much less of a legal or public health concern than teens using black market stuff at parties. But as with any recreational drug there are risks associated with marijuana use, even if the user is over the age of 60. The Han/Palomar study, for instance, found evidence for higher rates of nicotine dependence, cocaine use and prescription drug misuse among older Americans who had used marijuana in the past year. And dependency is always a concern, particularly among people who use marijuana frequently.

That said, it's becoming increasingly clear that stereotypes of marijuana users as risk-taking disaffected youth are outdated in the era of legal marijuana, with middle age and even older Americans becoming more likely to use the drug than their children and grandchildren.

This article was written by Christopher Ingraham, a reporter for The Washington Post.