How do I find out if an author is a crackpot?

So, someone in a comment thread on my friends list pointed to a book by Thomas Dalyrimple, in which he claims that opiate addiction is a myth, and that, indeed, nobody ever gets addicted to opiates; they just THINK they do, and society coddles them.

Something like that, anyway.

How do I find out if he's a crackpot, or if his ideas are worth considering?