Amgen says obesity drug caused up to 20% weight loss after a year, but shares drop 10%

Amgen on Tuesday said its experimental weight loss injection helped patients with obesity lose up to 20% of their weight on average after a year in a critical mid-stage trial, as the company races to join the booming obesity drug market. 

The drug, MariTide, also helped patients with obesity and Type 2 diabetes lose up to 17% of their weight after a year. The company said it did not observe a plateau in either group of patients, which indicates the potential for further weight loss beyond 52 weeks. MariTide was taken monthly or even less frequently in the trial — which could offer an advantage over the popular weekly injections on the market.

But shares of Amgen fell about 10% on Tuesday, as the results appear to be at the lower end of Wall Street's lofty expectations for the drug. Ahead of the data, several analysts said they wanted MariTide to show weight loss of at least 20% in the phase two trial, with some hoping for up to 25%. 

Wall Street has been eagerly awaiting the trial results, which shed light on how Amgen's drug may measure up to blockbuster weight loss injections from Novo Nordisk and Eli Lilly and a crowded field of treatments being developed by other drugmakers.

Amgen only released data on the first of two yearlong parts of the trial, which was designed to test different dose sizes, schedules and regimens of MariTide. The trial's main goal was to measure the amount of weight loss, but it also examined how long participants could go between injections and still lose pounds.

Notably, Amgen said patients who received the highest dose of MariTide every other month experienced comparable weight loss to those who took it monthly, suggesting the potential for less frequent dosing of the drug.

Roughly 11% of patients