Yes, we take requests . . .
A reader inquires about the process of new drug development and approval. A vast subject indeed. First, I definitely recommend as a good critical introduction Marcial Angell's piece in the New York Review of Books (yes, yes, effete east-coast pointy-headed intellectual elitism) from 2004.
Without trying to do it justice, I'll summarize one of her main points by saying that the profit motive leads drug companies to direct their efforts toward maintaining monopolies on drugs that they can sell a lot of, at a high price. Once they lose their time-limited exclusive rights to sell a drug, it's far less profitable for them. They have concluded that the best way to maintain profitability is not to try to develop novel treatments (and most of the creative energy that does lead to new therapies comes out of publicy-funded research anyway), but rather to develop slightly different versions of old drugs that they can get new patents on. Then, when their old drugs lose patent protection, they can use their enormous marketing budgets (considerably higher than their R&D budgets) to convince doctors to prescribe the new, still very expensive patented drugs instead of the now cheap generics, even though the new drugs aren't really any better, at least not for most patients. (Viz., Cox-2 inhibitors vs. NSAIDS; nexium vs. prilosec and even, for many folks, Tums. Etc.)
There are many other problems. Since the drug companies fund and control most of the clinical trials themselves, they can produce both subtle and unsubtle pressure to get favorable results and suppress evidence of harm. In particular, they don't have to test their new compounds against existing treatments, but only against placebos, or they can test them against sub-optimum versions of existing treatments (such as insufficient doses). So a new drug can be approved even if it isn't any better than existing drugs, or is actually worse. Also, the companies aren't particularly interested in finding adverse effects, obviously. It wouldn't be possible to find all the risks and side effects of new drugs prior to approval and marketing, for various reasons, but we could do much better, and all you need to be convinced is one word, Vioxx.
I could go on and on, but in answer to the reader's specific question, about drug companies selling rights, the key is that there are actually two kinds of exclusivity that they get: a patent on the compound, and marketing rights from the FDA. Once a compound is approved for one use, doctors can legally prescribe it even for unapproved, so-called "off-label" uses, but the companies aren't allowed to market it for those uses. So, in order to get marketing rights, they need to do a clinical trial to show (at least ostensibly) that it is effective for a given condition. A company might decide to sell the rights to conduct such a trial and market a drug on which it holds a patent for some new purpose, which is what appears to have happened in the case of Pfizer selling rights to a drug to be marketed as a treatment for stuttering. I have found that there is anecdotal evidence that drugs for anxiety -- such as Xanax -- may help some stutterers, since stuttering is compounded by the social anxiety that it causes for some people. Presumably Pfizer didn't think the stuttering market corresonded to their vastness, so they sold the rights to a smaller company to try to get a drug approved for the purpose.
This isn't necessarily a bad thing per se, but the standards for getting already licensed drugs approved for new indications are ridiculously low. This is often done with very perfunctory, small trials. That's why you see SSRIs now advertised heavily on television for everything from shyness to compulsiveness. It's very doubtful that they really help very many people with those problems. Of course, they don't do a whole lot for depression either.
See my post on Stayin' Alive about Bidil, for a particularly egregious example.