The launch of weight-loss pills is the hottest battle in pharma. So far, Eli Lilly is losing to rival Novo Nordisk. Since its obesity pill Foundayo hit the market in April, Lilly has captured about 11% of the prescription volume for new pills, according to the latest weekly data.

Novo Nordisk's Wegovy pill, which launched in January, commands the rest. It is a remarkable turn of events for the near $80 billion anti-obesity market, among the hottest in the industry. Lilly dominates sales of shots.

Analysts figured the company's pill would similarly crush it. Among the challenges, doctors say, is study data indicating that people taking Novo Nordisk's pill lost an average of 16.6% of body weight after more than a year, versus 12.4% for Foundayo.