I'm guessing you had this in mind already, but to clarify anyway, there's a pretty major availability bias since anything celebrities are involved in is much more likely to be reported on, leading to a proliferation of news stories about celebrities with addiction problems.

On the other hand though, celebrities are a lot more likely than most people to simply be given drugs for free, since drug dealers can make extra money if their customers are enticed by the prospect of being able to do drugs with celebrities. And of course that's aside from the fact that the drug dealers themselves can be enticed by the star power and want to work their way into their circles.