When stand up comedians Tommy Chong and Cheech Marin released their classic stoner comedy Up In Smoke, back in 1978, they didn't expect the film to have as much of a cultural influence as it did. The film broke new ground for comedies and helped create an entire sub-genre of stoner comedy films which have come to include classics such as Friday and Half Baked

40 years later, however, the two stars of the film have revealed a terrible secret. In a lengthy profile with Rolling Stone, Cheech admits that throughout the whole production of Up In Smoke, the two were never high on set once.

"We maybe smoked after shooting," said Cheech, "but not when we’re working. We had to sustain a level of energy, especially making movies. We had long days on set. If we got stoned, we wouldn’t get it done."

As it turns out, all those massive joints that Cheech and Chong smoked throughout the film were filled with something other than that loud. The director, Lou Adler, claims they were smoking on lettuce, though Chong recalls rolling up tobacco or "herbs from India."

"We got high [socially] but we couldn't do it with dope," he says. "We couldn't do those big joints," said Chong. 

Apologies to those who have had their 4/20 ruined by this horrible news. Hopefully the film will still hold up now that Cheech and Chong's dark secret has finally come to light. Check out the rest of the interview for tons of interesting anecdotes about the creation of the film.