Is running a marathon on a GLP-1 a bad idea?
Runners describe nausea, heart-rate spikes and under-fuelling after starting tirzepatide or semaglutide during race training. Sports dietitians quoted say endurance athletes risk low energy availability and generally shouldn't start a GLP-1 mid-training, and experts warn against splitting doses, since that isn't how the drugs were studied.
Source: The Guardian (27 Oct 2026). Image: The Guardian.