A type of contraceptive injected once a month is being recalled because some doses may not be potent enough, the manufacturer announced Thursday.
A subpotent dose may not be effective in preventing pregnancy.
Pharmacia Corporation of Peapack, N.J., said the recall covers Lunelle monthly contraceptive in prefilled syringes.
As many as 100,000 women could be affected by the recall, covering products distributed between January and October of this year, the Food and Drug Administration reported.
The recall does not include the form of Lunelle packed in vials, the company said, but only the prefilled syringes which constitute the majority of the market.
When the drug won approval in 2000, the company said it was 99 percent effective.
Pharmacia spokeswoman Caroline Bullock said the company has not seen any increase in unintended pregnancies among users of the drug.
Women who used the contraceptive may not be aware if they received the prepacked form or that drawn from a vial. Pharmacia urged women who have been using Lunelle to contact their physician about another form of contraception and begin using an additional barrier form of contraception in the meantime.
Lunelle is an alternative to another injectible contraceptive, called Depo-Provera, that lasts three months. Like many birth-control pills, it works through a combination of the hormones progestin and estrogen.
Women taking the contraceptive injection still have monthly menstrual cycles.