Amgen's long-acting experimental obesity drug MariTide needs to be given at a low starting dose to limit side effects like vomiting, according to mid-stage trial results presented at a medical meeting on Monday that pushed the company's shares down nearly 6%.

Some new medications in development are also trying to solve for a persistent side effect of existing drugs: Patients who lose fat also tend to lose muscle. This can be particularly dangerous for older adults because it makes them more likely to fall and can worsen osteoporosis.