Amgen Inc.’s migraine attack suppressant, Aimovig, has been granted marketing approval by the Japanese Ministry of Health, Labour and Welfare, the Thousand Oaks company announced Wednesday.

More than half a million patients worldwide are prescribed Aimovig. It was approved in the U.S. in 2018.

The drug is the first and only approved treatment in Japan to block a gene-related receptor that is believed to play a key role in migraine headaches. Aimovig also marks the first independent submission and approval for Amgen K.K., an Amgen affiliate based in Tokyo.

Aimovig’s approval was based on two studies, one phase II study that analyzed the safety and efficacy of the drug in adult Japanese patients with episodic migraines and a phase III study that analyzed the same factors for patients with both episodic and chronic migraines. Aimovig significantly reduced monthly migraine days in both studies.

According to the Japanese Headache Society, in Japan, more than 70 percent of patients with migraine have never visited a hospital for treatment. Also, around 50 percent of patients try to treat their migraines with over-the-counter medications.

“We want patients to know they don’t need to push through this disease alone. If properly treated with a therapy like Aimovig that has proven efficacy and has an established tolerability profile, they may be able to take on day-to-day tasks and challenges they had previously been forced to give up,” Steve Sugino, general manager at Amgen K.K., said in a statement.

Shares of Amgen (AMGN) closed Wednesday down $1.20, or a fraction of a percent, to $238,71 on the Nasdaq, on a day when that market closed up a fraction of a percent.