The biggest quandary in the obesity drug market is that nobody knows just how big it will be. Everyone agrees it’ll be huge—currently, Eli Lilly & Co. is worth more than Tesla Inc., and Novo Nordisk A/S is at times the most valuable company in Europe. But just how many people will eventually take drugs like Wegovy and Zepbound, better known by the names of their diabetes counterparts Ozempic and Mounjaro? How long do patients need to stay on the drugs? Will the market be merely massive, or truly gargantuan?