When actors play drug addicts in movies, are they affected by the drugs they have to take?

@LoveBeingWatched So when they stick a needle in their arm, what are they really injecting themselves with?

@EstrellaStarr saline fluid most likely.

@LoveBeingWatched If you say so.

@EstrellaStarr just my thoughts. I could be 100% incorrect.

@LoveBeingWatched There’s a science to the way the effects are faked.
https://nypost.com/2013/10/23/what-actors-really-snort-shoot-and-smoke-on-set/