WASHINGTON (AP) — The Food and Drug Administration is warning about the overuse of testosterone-boosting drugs taken by millions of U.S. men, saying the popular treatments have never been proven safe or effective for treating common signs of aging like low libido and fatigue.

The agency says drugmakers must clarify that their drugs are only approved to treat low testosterone levels caused by disease or injury, not general aging. Additionally, the FDA warned Tuesday that the drugs can increase the risk of heart attack and said drugmakers must add that information to their warning labels.

The federal rebuke comes after years of industry marketing for new pills, patches, gels and injections that promise relief from low testosterone or “Low-T.” The advertising blitz has pushed sales of testosterone drugs to over $2 billion.