A fascinating medical detective story about the unusual reception for a promising new drug by a skeptical medical community reluctant to abandon its age-old Hippocratic Oath of "Do No Harm." Stewart Justman explains how a pill called finasteride, proven to dramatically reduce the incidence of prostate cancer, was found to be also associated with a distinctly higher rate of aggressive cancer. As urologists and oncologists were presented with a strange mix of eurekas and cautionary notes, physicians adhered to their best principles and remained wary of massive application. For now, the drug is deemed too risky: the medical dictum of avoiding harm has inhibited its use on a grand scale, though statistically there is much in its favor. Do No Harm is engrossing reading about medical science and, finally, a reassuring tale of the triumph of tradition over novelty.