You only have to trawl the conspiracy forums to see that there are a lot of myths surrounding medical trials - also known as, clinical trials, or drug trials - floating around the internet. While the medical profession isn't devoid of scandal, there's more mess to be found in junk yards than clinics and laboratories, where highly qualified professionals work to develop the drugs of the future, and covering up is much easier in politics than medical testing.
In Europe, clinical trials are heavily regulated by EU directives and the domestic laws within each member state. In the UK, an Ethics Committee will scrutinize each trial proposal to see if it meets minimum standards before being granted approval. These standards are in place to protect both the volunteer and the sponsor, and to ensure the drug in question can undergo the best possible trial.
Companies sponsoring a trial spend millions developing the drugs they wish to test. Their investigations into the performance of the drug must be distinct and their raw data devoid for anything that could compromise its efficacy. All of this is before the drug is licensed. Yes, mistakes happen but these errors are inevitably rooted out and the right people are compensated.
When volunteers sign up, they can do so in the knowledge that their rights are protected under the law and nothing can happen to them without their consent.
Signing up for a long term medical trial where you must live at the trial clinic and be subject to restrictions doesn't mean you are imprisoned for the duration. You are free to leave if you want to. There is a protocol and volunteers are made aware of it before they give their consent. In some trials there are restrictions around when volunteers can eat, what they can eat, etc. All of this is clarified at the pre-trial consent talk and consent is a legal necessity before a volunteer can participate.
Healthy volunteers are paid an honorarium in exchange for their time and commitment to the clinical trial. Honorariums are typically paid at the end of the last day. If a volunteer chooses to leave before the end of the trial, it will affect the amount they receive, which will reflect the time spent at the trial. Clinic staff will discuss how a volunteer is paid when they decide to withdraw.
Some trials are condition-specific, such as cancer trials. The opportunity to participate in a clinical study is also the opportunity to receive new treatments that could speed up recovery, as well as the chance to contribute to developments that could save the life of someone you've never met, but who shares your disease. Placebos in condition-specific trials are rare and if they are used, it will be stated prior to the start of the trial.
You can find out more about volunteering for a medical trial here.