While movie stars aren't drug-free zones, movie sets are at least supposed to be. Which is why, during filming, actors have to make do with stunt-double drugs. An article in Wired neatly summarises some of the most common stand-ins; here are a few of the best.
Methamphetamine Taking huge quantities of real meth can lead to all sorts of crazy adventures. The most likely side effect of taking the meth cooked up in Breaking Bad? A cavity. The drug was substituted for rock candy.
Cocaine Of all the drugs floating around the streets, cocaine ought to be one of the easiest to fake. Still, legend has it that, during the filming of Scar Face, Al Pacino had to resort to the real stuff. Not so these days: in 2001′s Blow, the cast snorted inositol — powdered vitamin B.
Crack In indie film Half Nelson, prop artists took pieces from a broken mug and dyed them with coffee to replicate crack. Because those pieces don't really behave like the drug, they then had to use a little tobacco to create the associated smoke. All of which is, apparently, slightly less morish than the real thing.