The first generic version of the popular Advair asthma inhaler has been approved by U.S. regulators.

The Food and Drug Administration today approved Mylan’s version in three strengths for ages 4 and up.

The inhalers are used twice daily to keep airways open and prevent flare-ups of wheezing, shortness of breath and other symptoms of asthma or chronic obstructive pulmonary disease. About 42 million Americans have those conditions.

The device contains two medicines, inhaled in a precise mixture. That complexity has stymied a couple of other companies developing generic versions of GlaxoSmithKline’s Advair Diskus inhaler, which costs about $400 a month.

Generics generally are cheaper. Mylan didn’t immediately respond to queries about when its inhaler, called Wixela Inhub, will be available or what the price will be.