For the third time in less than a year, a pharmaceutical company has recalled its birth control pills due to a packaging error.

Sandoz, the generic pharmaceutical unit of Novartis International AG, announced Tuesday that it is recalling 10 lots of its Introvale birth control pills (the company did not specify how many pills are in 10 lots).

According to NPR, a consumer alerted the company that its placebo pills were misplaced in the blister packs, which could cause women to take the wrong pills at the wrong time and become inadvertently pregnant. Pharmacies distributed the affected pills between January 2011 and May 2012.

Sandoz’s announcement highlights a worrisome problem among oral contraceptive makers. In February, Pfizer Inc. recalled nearly 1 million of its birth control pills due to a similar packaging error. And in September 2011, Qualitest Products Inc. recalled 1.4 million of its birth control pills, which were mistakenly misaligned during production. Qualitest’s error led to a lawsuit. Lauren Betancourt sued the drug maker because she unintentionally became pregnant after taking placebo pills at the wrong time.