ABSTRACT
Many human activities that confer enormous benefits also entail risk. Consider, for example, the use of pharmaceuticals. Although modern drugs have saved untold numbers of human lives, the use of new drugs or vaccines always has some potential for unexpected con sequences. But quantifying risks is seldom a simple task. The side effects of a drug can manifest themselves in myriad ways, and re searchers typically test the allergenicity and toxicity of new drugs, screen for effects on different organs and organ systems, and even look for long-term delayed effects. To be safe, drug trials should also examine subjects who vary in age, sex, and physical condition, while guarding against interactions with other drugs. Even after well-replicated drug trials have been completed, some level of scientific uncer tainty regarding risks will always persist, because some serious consequences may only manifest themselves under extremely rare conditions or only after long exposures.
