Suicide takes the lives of around a million people each year, most of whom suffer from depression. In recent years there has been growing controversy about whether one of the best-selling anti-depressants - selective serotonin reuptake inhibitors (SSRIs) - increases or decreases the risk of completed suicide. Randomized clinical trials are not informative in this application because of small samples and other problems. We present what we believe are the most scientifically credible estimates to date on how SSRI sales affect suicide mortality using data from 26 countries for up to 25 years. We exploit just the variation in SSRI sales that can be explained by institutional differences in how drugs are regulated, priced, and distributed, as reflected by the sales growth of new drugs more generally. We find an increase in SSRI sales of 1 pill per capita (12% of 2000 sales levels) reduces suicide by 5%.