Doctors may just use the drug off-label. If the patient responds then they use the drug, otherwise they try something else. A formal trial really helps very little in these cases.

If a bunch of clinicians find that the drug is effective against the condition, they can (as has happened so many times) make their own study to popularize the usage.

Remember: The safety of the drug is not in question, just the efficiacy.

But how do physicians know it works if trials aren't run? You can't go by anecdotal evidence.

Hell, look at the huge niacin trial that Merck ran. Doctors have been prescribing it for 30 years and you know what? It doesn't help. Unless a massive clinical trial was run, you'd never know whether it was worth prescribing.

This is a valid point. While I won't dive into the qualms that stem from pharma companies funding and subsequently selectively choosing their trials, the case with BiDil is particularly curious [1].

When BiDil was patented, studies were carried out using _only_ African-American subjects, such that the race-specific efficacy was never actually tested. As such, the basis for the entire patent, which hinged on race specificity, has been challenged by some in the field. In my post above there's a link to a paper that came out one of the trials.

[1] - If you're interested, Ben Goldacre has a really interesting talk on the subject.

http://www.ted.com/talks/ben_goldacre_what_doctors_don_t_kno...

FDA already gives a special monopole privilege after clinical trials. FDA want to encourage companies in doing clinical trails, including on drugs which has an expired patent.

Evergreening is companies seeking monopole privilege after that original patent protection and the FDA protection has expired. Nothing to do with clinical trials.