Re: False, Injurious Statements and Libel...

If you publicly defame someone and damage his reputation, it does not matter whether or not you believe what you said. You presented false, injurious and untrue statements as facts, which are provably not true and therefore you committed libel. Whether, or not you believed it yourself is irrelevant.

I agree with what you said here. If I believe X is on drugs and go on to state without qualification that "X is on drug Y" (or "on drugs") without having evidence to prove it as true, it could turn out that I am guilty of libel because it was not in fact true.

The statement "I believe X is on drug Y" is not a false statement, at least not provably. (I could say "I believe the sky is made of cotton candy" and it would be false, but not provably so.)

"X appears to be on drug Y because people on drug Y share characteristic Z with X" is a more reasonable statement that is also not necessarily logically untrue (if the characteristics are as described). But the evidence is indirect -- since there are other possibilities that could explain their behavior.

A more grey area would be whether "X is on drug Y" is libelous when it turns out they actually are on drug Y. If you could prove in court that they are on drug Y, would that free you from libel charges? My suspicion is that different jurisdictions have defined this differently. In my opinion, the crime was making the assertion (as fact) without having proof at your disposal.