Amgen (AMGN.US) said on Tuesday that its experimental weight-loss injection MariTide helped obese patients lose an average of 20 percent of their weight, a year after a crucial mid-term trial. However, the stock fell more than 11% before closing.

The company points out that MariTide can help people with obesity and type 2 diabetes lose up to 17% of their weight after one year. The company added that no platform period was observed in the two groups of patients, indicating that weight loss could be further after 52 weeks. MariTide is injected once a month in the trial, even at a lower frequency, which may have an advantage over the popular weekly injection on the market.