Many chronic illnesses that affect the working population can cause losses in productivity. The extent to which these productivity losses can be reduced by pharmacological treatment is of particular interest to employers, who bear the productivity costs and subsidize the cost of employees' health care. In the past several years, the effects of pharmaceuticals on productivity losses have been tested in numerous studies, including randomized, double-blind, placebo-controlled trials. In this article, we summarize and critically review these studies and, where appropriate, provide quantitative overviews. The evidence is very good for about a dozen drug classes that pharmaceuticals reduce productivity losses caused by respiratory illnesses (ie, asthma, allergic disorders, bronchitis, upper respiratory infections, and influenza) diabetes, depression, dysmenorrhea, and migraine. We also discuss the calculation of productivity costs, reductions in which may partially or completely offset the costs of treatment. This information should be helpful to occupational physicians who are increasingly providing recommendations on employer benefit plan designs and pharmaceutical benefits.