This 2018 paper substantiates previous evidence indicating metformin diminishes the beneficial effects of exercise on insulin sensitivity. Metformin is the most widely prescribed medication for the treatment of Type 2 diabetes and more recently has been promoted as a general anti-aging drug. However, this trial’s authors observe that taking metformin alongside exercise inhibits two of the major benefits attributed to exercise (improvements in insulin sensitivity and cardiovascular fitness). They thus suggest recommendations to prescribe metformin broadly as an anti-aging medication are premature, as the drug may accelerate key elements of age-related metabolic degeneration.