Let me explain for the scientifically unaware amongst you. Scientific knowledge is never certain, it is a question of probability. For any question asked in science (e.g. Does drug A have a beneficial effect on condition B?) there will be experiments done that give a "yes" answer, and others that give a "no" answer. All of the answers put together, with due consideration to the relative quality of the different experiments done, will give us an approximation to the truth based on the balance of probabilities. So if a drug company publishes the "good" (for them) studies and bins the "bad" ones, their drugs can get licensed for sale even though they may do no good at all. And since all drugs have side effects, these bogus medicines may do more harm than good.
We quacks often get it in the neck from critics for not having science behind us. It is true, we don't. But equally, when those who do have the money to carry out proper trials on their methods systematically cook the books, it is not encouraging.
* "Drugs firms 'risk lives by hiding bad trials'", Daily Mail, 24 October 2012.