As a rule, actors who smoke onscreen aren't actually inhaling any chemicals -- even nicotine. ("Herbal cigarettes" are standard on smoking-heavy sets like Mad Men). But every once in a while, the actors onscreen are getting into character by inhaling for real.

Peter Fonda, star of the 1969 cult classic Easy Rider, has admitted for the first time that he smoked real marijuana in the film. The scene in question also involves director/star Dennis Hopper and Jack Nicholson. Busted!

Most directors couldn't get away with making their actors consume drugs on camera. Even Easy Rider, a counterculture movie about hippies (Fonda and Hopper) riding motorcycles across America, didn't go all the way: Fonda says there was no real LSD involved in the famous acid-trip sequence. "We did not take LSD, no matter what the rumors say...You can't make a movie when you're ripped like that," he insists. And powdered sugar was used in place of cocaine -- "Man, that stuff burned!" Fonda says.

Many other films are rumored to contain actual marijuana use, including Pineapple Express (starring real-life recreational users Seth Rogen and James Franco), all the Kevin Smith movies featuring potheads Jay and Silent Bob, and every Cheech and Chong comedy.

Drug movies that get a clean bill of health include the recent Taking Woodstock -- director Ang Lee said recently that he refused to even try marijuana in preparation for making the film.

Do you think it's okay for actors to light up to get into character? Chime in below!