As the popularity of drugs such as Novo Nordisk’s Ozempic and Eli Lilly’s Mounjaro grow rapidly, patient testimonies have focused not only on the dramatic weight-loss effect but also on how quickly many seem to regain weight if they stop taking the injections. Investors can get excited by a product whose target market is so large (apparently more than 40 percent of American adults are obese) and the medicine must be taken indefinitely.