A Giant Bug

Okay, this is a crazy question but one that i have to ask cause i have always wondered what movie this scene takes place in. One night on basic cable i caught this scene and it's often haunted me because i have a bit of a fear of bugs, spiders, etc. Anywho, it seems that it would most likely be a movie that has something to do with drugs. The scene is this. There's a guy freaking out in a bathroom shower screaming while a giant green bug like thing is attacking him. the bug looks kind of like a giant fly but it's green all over. I have seen it parodied a couple of times, but i've never actually figured out what this film scene comes from. Anyway, i didn't know if it was this movie or another drug movie. If anyone knows what this movie is it would be awesome. Thanks. I know this is a crazy question, but i'm a crazy person. just need to figure this out. i'm thinking it's some movie that was made in the seventies or so.