Amgen Shares Drop Nearly 6% as AMG 133 Phase II Obesity Trial Misses Heightened Market Expectations

▎Armstrong

On June 23, 2025, Amgen's GIPR antibody fusion GLP-1 new drug AMG 133 weight loss Phase II clinical data was published in the New England Journal of Medicine.

For the obesity cohort, AMG 133 treatment resulted in a weight loss of 16.3%-19.9% (based on efficacy) after 52 weeks, and a weight loss of 12.3%-16.2% according to the Treatment Policy Estimand (TPE).

In terms of safety, the proportion of patients discontinuing treatment due to adverse effects in different dose groups of AMG 133 were 14%, 14%, 22%, and 29%, respectively. The majority of discontinuations were attributed to gastrointestinal side effects, with severe adverse effect rates at 5%, 5%, 6%, and 14%.

Amgen's AMG 133 weight loss Phase III clinical trial is currently in the enrollment process, with plans to initiate Phase III clinical trials for atherosclerotic cardiovascular disease, heart failure, and obstructive sleep apnea in 2025.

MarTide is different from other multi-target GLP-1 classes as it is formed by fusing a GIPR antibody with GLP-1.

Summary

AMG 133 previously achieved a 16% weight loss in 12 weeks in Phase I clinical trials, continuously raising market expectations. The Phase II clinical data disclosed this time shows a 52-week weight loss.16.3%-19.9% (based on efficacy, placebo was -2.6%), or 12.3%-16.2% weight loss according to the Treatment Policy Estimand (TPE) (placebo was -2.5%).As a once-monthly weight loss drug, its efficacy has been quite good, but it did not meet the already heightened market expectations, and the gastrointestinal side effects were significant, with nearly 30% of the high-dose group discontinuing the medication. On the same day, Amgen's stock price fell by 5.8%, with its current market value at $146.5 billion.