Health Canada says women who take Marvelon 28 should be aware of an issue with certain lots of the birth control pills.
The affected packages do not include day-of-the-week stickers that are meant to be applied on the blister pack containing the pills.
The stickers identify the first day of the week when the medication is started and the weekdays that the pills should be taken, an advisory issued by the agency notes.
The stickers may be used by women to help them remember if they took their daily pill on a given day, and there may be an increased chance of missing a dose without them.
Merck Canada Inc., the importer of Marvelon 28, will begin distributing day-of-the-week stickers to pharmacies this week. The stickers will be available at no additional cost.
Health Canada advises the pills are safe and effective to use, and women should continue to take them as prescribed, being cautious to keep track of when they are taken to avoid missing any doses.
The advisory notes that Marvelon 21 is not affected by the issue.