I think there should be legislation that forbids the assessment of penalties in research studies or clinical trials, for those who withdraw. Why should a patient give up his or her rights for a future benefit to others, without choice? That is what was done, albeitly in a twisted way, in the twin studies by Dr. Mengele in WWII concentration/death camps. If there aren't enough patients as a result of withdrawal(s) by patient(s), then postpone the study/trial and review the incentives for participation. Also, there have been a number of toxic reactions to experimental substances, especially in cancer research, resulting in Grade 3/4 reactions. Patients often know that something weird is happening in their body, and they have a right to put a stop to that, or even something as mundane as just changing their mind. Ironically, the assessment of penalties for changing one's mind will drive more people away from participating in the first place, than anything else, especially in these hard economic times. That is my opinion, for what it is worth.
Here is the journal abstract link:
http://bioethics.net/journal/j_articles.php?aid=2502&display=abstract