I believe that the major considerations are honesty, informed consent, safety, and patient benefit. These appeal to a significant segment of the population who neither have the means nor the information to obtain the care they need. This means that neither the investigator nor the volunteer knows the form of treatment each subject is receiving. Many do receive a placebo or ineffective treatments. This must be made clear to all participants.
Drug trials are generally time limited.
These projects continue for only a set period that can vary from days to a year or more. If the interval statistical analysis shows that the compound being evaluated is doing poorly, that project will be stopped abruptly. The drug companies rarely make any provision for continued treatment at the conclusion of the study, although humanitarian extensions of the research protocol do occur. It is also common for some drug houses to provide the experimental compound free of charge to volunteers until the research medication is available commercially. This is especially true in schizophrenia research.