US Marijuana Use Peaked Around 1985: Use Among Young Adults Declining Since Mid-80s: Only 7 Percent Of Americans Currently Use Marijuana

From Gallup, "In U.S., 38% Have Tried Marijuana, Little Changed Since '80s: Fewer young adults have tried it today compared with in the 1970s and 1980s" by Lydia Saad:

Even as Americans' support for legalizing marijuana has doubled, and more than 20 states have loosened marijuana restrictions in various ways, Gallup finds relatively little increase throughout the past three decades in the percentage of U.S. adults who say they have tried marijuana. ***Gallup's trend by age reveals that widespread experimentation with marijuana first occurred among adults aged 18 to 29 between 1969 and 1973, rising from 8% to 35%. It then continued to mount, reaching 56% by 1977, and remained at that level in 1985. Since then, however, marijuana use among young adults has progressively declined. At the same time, as the bulge of young adults who tried marijuana in the 1970s ages and replaces older Americans who never tried it, the rate of all Americans who have ever tried the drug has increased slightly.

Source: Gallup

Although more than one-third of American adults have tried marijuana, a much smaller percentage admit to currently using it. Seven percent of U.S. adults in the July 10-14 survey -- a separate half-sample from the one asked if they have ever tried it -- say they smoke marijuana.