Teva Pharmaceutical (NYSE: TEVA), which is known for its generic-drug business but has some branded drugs as well, is getting a taste of its own medicine as the Food and Drug Administration approved a generic version of its asthma drug ProAir HFA, which was developed by Perrigo (NYSE: PRGO). ProAir HFA is one of the most commonly used rescue inhalers in the U.S., with North America sales up 77% year over year to $80 million in the fourth quarter of last year, although the increase was due to higher sales reserves recorded in anticipation of generic competition. For the year, sales of the branded drug were down 31% as Teva launched an authorized generic of the drug in January 2019. Image source: Getty Images. Inhalers tend to be hard to copy because they require duplication of both the active substance, which is needed for all generic drugs, and the delivery device. For example, Advair, an asthma drug from GlaxoSmithKline (NYSE: GSK), was able to get a few years of extra exclusivity because generic-drug makers weren't able to meet the FDA's requirements until Mylan achieved the goal last year. Through the Generic Drug User Fee Amendments, the FDA has pledged to support the development of complex generic-drug products such as inhalers. The agency is also committed to adjusting its focus on approvals from first-in-first-out to drugs, such as ProAir HFA, that don't have any generic competition. In fact, the office of generic drugs gives priority to applications up to the third generic drug because that's where the largest price drop occurs. 10 stocks we like better than Teva Pharmaceutical IndustriesWhen investing geniuses David and Tom Gardner have a stock tip, it can pay to listen. After all, the newsletter they have run for over a decade, Motley Fool Stock Advisor, has tripled the market.* David and Tom just revealed what they believe are the ten best stocks for investors to buy right now... and Teva Pharmaceutical Industries wasn't one of them! That's right -- they think these 10 stocks are even better buys. See the 10 stocks *Stock Advisor returns as of December 1, 2019 Brian Orelli and The Motley Fool have no position in any of the stocks mentioned. The Motley Fool has a disclosure policy.Source