Amgen will charge $6,900 a year for a new drug that can spare migraine sufferers a few headaches each month, a price that comes in well below Wall Street expectations as the company hopes to avoid the payer backlash that has hamstrung recent drug launches.

In clinical trials, patients who took Amgen’s drug experienced about two fewer migraines per month compared to those who got placebo. Doctors have described the effect as modest, but the difference was enough to convince the Food and Drug Administration, which approved the treatment Thursday.