Amanda Bynes -- 'I DON'T DO DRUGS!'

Amanda Bynes just tweeted something the cops clearly aren't buying -- she says she's drug free.

Amanda says, "I only smoke tobacco. I don't drink or do drugs." She adds, "I've never had a bong in my life!"

As you know, Amanda has been accused of smoking pot in her apartment and then throwing a bong out the window after police entered.

And there's more. Amanda says, "I need to get another nose job after seeing my mugshot!"