Mylan (MYL) has been approved to make a generic version of migraine headache medicine Imitrex from GlaxoSmithkline and is set to ship the drug immediately.

The tablets - whose scientific name is Sumatriptan Succinate - will be sold in 25mg, 50mg, and 100mg amounts to begin shipping immediately, Mylan said in a press release today just ahead of the stock market’s regular trading close.

Shares of Mylan ended flat today at $13.22 per share.

The U.S. Food and Drug Administration accepted the Abbreviated New Drug Application for the drug, which is manufactured in Mylan’s Morgantown, West Virginia facility, the company said in a statement.

ANDA applicants must show their generic product performs in the same way as the original “innovator” drug.

Over the 12 months ending June 30, Sumatriptan Succinate tablets had sales of $934 million, according to IMS Health.