Botox, commonly used for anti-wrinkle treatments, was approved as a drug for chronic migraines in 2010, but some patients claim it isn’t very effective.

In a recent study from the Journal of American Medicine Association, researchers compared the effects of Botox and placebo for migraine treatments.

Based on the findings, Botox injections aren’t effective for preventing migraines for people who suffer them less than 15 times a month. The same can be said about patients with chronic-tension headaches.

Researchers said that the Botox migraine treatment is subjective—it works for some, but doesn’t for others. While it can be ineffective for some, it can be dramatically effective for others.