Pharmaceutical company Pfizer (NYSE: PFE) announced Wednesday a recall of one million birth control packets due to inconsistencies in the drug. The error, which Pfizer has attributed to a mechanical failure, could leave women at risk for pregnancy due to differences in hormone levels in the pills.

The recall affects 14 lots of Lo/Ovral-28 tablets and 14 lots of Norgestrel and Ethinyl Estradiol tablets, the generic version of the drug. The birth control pills are all marketed in the U.S. by Akrimax Rx Products and are  manufactured by Pfizer.

The pills in question come in packets of 21 active hormonal pills, and seven inactive pills. Some packets may contain the wrong number of inert or active ingredient tablets, and the tablets may be out of sequence, according to a press release from Pfizer.

The pills, Pfizer said, have been distributed to warehouses, clinics and retail pharmacies nationwide. The only flaw in the drug is the packaging, and Pfizer stressed that the defects in the packs do not pose any immediate health risks to individuals taking the pills. However, “correct dosing of this product is important in avoiding the associated risks of an unplanned pregnancy,” said Pfizer in the release.

Patients who find they have the affected pills should notify their doctor and return the pills to their pharmacy for an exchange. The affected pills have expiration dates ranging from July 31, 2013