Every year millions of Americans (no one knows exactly how many) volunteer to be human subjects in medical research that compares a new treatment with an old one—or when there is no existing treatment, with a placebo. By something like a coin toss, some volunteers are assigned to get the new treatment (the experimental group), while others get the old one (the control group). This type of research is termed a clinical trial, and at any given time there are thousands underway in the US. Most are sponsored by makers of prescription drugs or medical devices, but many are sponsored by the government, mainly the National Institutes of Health (NIH). A growing number are conducted offshore, particularly in countries with autocratic governments, where they are easier and cheaper to do.

The first modern clinical trial was published only sixty-seven years ago, in 1948. Sponsored by the British Medical Research Council, the trial compared streptomycin, a new antibiotic, with bedrest alone in patients with tuberculosis. (Streptomycin proved better, and became part of the usual treatment for this disease.) Before that, human experimentation was fairly haphazard; subjects were treated in one way or another to see how they fared, but there was usually no comparison group. Even when there was, the comparison lacked the rigorous methods of modern clinical trials, which include randomization to make sure the two groups are similar in every way except the treatment under study. After the streptomycin study, carefully designed clinical trials soon became the scientific standard for studying nearly any new medical intervention in human subjects.1

Patients with serious medical conditions are often eager to enroll in clinical trials in the mistaken belief that experimental treatments are likely to be better than standard treatments (most turn out to be no better, and often worse).2 Healthy volunteers, on the other hand, are motivated by some combination of the modest payments they receive and the altruistic desire to contribute to medical knowledge.

Given the American faith in medical advances (the NIH is largely exempt from the current disillusionment with government), it is easy to forget that clinical trials can be risky business. They raise formidable ethical problems since researchers are responsible both for protecting human subjects and for advancing the interests of science. It would be good if those dual responsibilities coincided, but often they don’t. On the contrary, there is an inherent tension between the search for scientific answers and concern for the rights and welfare of human subjects.

Consider a hypothetical example. Suppose researchers want to test a possible vaccine against HIV infection. Scientifically, the best way to do that would be to choose healthy participants for a trial, give the vaccine to…