INDIANAPOLIS (AP) — Pfizer Inc. is recalling 1 million packets of birth control pills due to a packaging error that could raise the risk of an accidental pregnancy by leaving women with an inadequate dose.

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 hormone tablets and 7 inactive sugar tablets to regulate the menstrual period while providing contraception.

The risk of an accidental pregnancy depends on how many doses a patient misses in the pill cycle, pharmacist Mike Parker said. Patients normally can miss a dose and then catch up the next day, but the risk rises if a woman goes more than a couple of days without the right dose.

Parker said birth control pills account for about 25 percent of the prescriptions filled at his store, Fred’s Neighborhood Pharmacy, in New Castle, Ind. But he doesn’t expect many worried calls from customers about this recall.

He said it focuses on an older pill that used to be popular but doesn’t sell as well anymore compared with newer versions that have fewer side effects.

“It’s not a No. 1 or No. 2 seller,” he said.

U.S. pharmacists filled 38.9 million birth control prescriptions in the first six months of last year, according to the most recent statistics from data firm IMS Health. A total of 78.6 million prescriptions were filled in 2010.

An IMS spokesman said the pills subject to the recall are not among the top 5 prescriptions filled.

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

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.

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

Copyright 2012 The Associated Press