Brief exposure with rapamycin has the same positive effects on lifespan and health in old age as a lifelong treatment, researchers show in fruit flies and mice. Rapamycin is currently the most promising anti-aging drug. To maximize the medicine's effectiveness, it is often administered for life. However, even at low doses used to prevent age-related decline, side effects can occur. Therefore, the shorter duration of treatment may make it more likely to be used in humans.