Amgen's experimental drug MariTide helped overweight or obese patients shed up to 20% of their body weight in a mid-stage trial, but the results failed to meet lofty investor expectations and shares of the biotech company tumbled about 12% on Tuesday.

Amgen also tested MariTide in a population with Type 2 diabetes, a group that tends to lose less weight with the new obesity drugs. On average they lost up to 17 percent of their initial weight.

Amgen Inc. shares fell the most in 23 years after its experimental obesity shot failed to significantly outperform rivals and showed a high rate of gastrointestinal side effects.The reaction shows how high the bar is for new weight-loss drugs.