From Scientific American:
Medical research can have big rewards—both in gratifying discoveries and in potentially turning them into profitable treatments. To achieve the former, researchers work hard. Very hard. To obtain the latter, they can start companies or sign commercial funding agreements—well before testing is over. So, do patients undergoing clinical trials for new treatments have a right to know about these monetary interests?
Legally, no. And no empirical data has tied researchers' financial interests in a study to negative outcomes for patients. In the past several years, however, more findings suggest that, ethically, patients should be informed prior to participating in a trial.