WASHINGTON (AP) — Pfizer Inc. is recalling 1 million packets of birth control pills because of a packaging error that could leave women with an inadequate dose of the hormone-based drugs and raise the risk that they will get pregnant accidentally.

The problem affects 14 lots of Lo/Ovral-28 tablets and 14 lots of generic Norgestrel and Ethinyl Estradiol tablets. Both products are manufactured by Pfizer and marketed in the U.S. by Akrimax Rx Products under the Akrimax Pharmaceuticals brand.

Pfizer found that some packets of the drugs had too many active tablets, while others had too few. Oral birth control products use a series of 21 drug tablets and 7 inactive sugar tablets to regulate the menstrual period while providing contraception.

A company spokeswoman said the problem was caused by both mechanical and visual inspection failures on the packaging line. She said the problem has been corrected.

Pfizer issued a statement saying the problem was identified and corrected immediately. The recall is not related to safety but does raise the risk of unintended pregnancy. Patients with the affected lot numbers should return them to the pharmacy.

The affected packets have expiration dates ranging between July 31, 2013, and March 31, 2014. Lot numbers are available at http://www.fda.gov/Safety/Recalls/ucm289770.htm

The drugs were distributed to warehouses, clinics and retail pharmacies throughout the U.S.