Bristol-Myers Squibb Co. says it is recalling eight production lots of its anti-clotting drug Coumadin because the amount of the active ingredient in the drug could change.

The company says the recall is a precaution and no side effects have been reported. Bristol-Myers Squibb is recalling five production lots of Coumadin hospital unit doses and three lots of physician samples. All of the recalled products are in 1-milligram tablets. The New York company says the level of a compound in the tablets could change over time, affecting the level of the active ingredient.

The tablets have expiration dates between June 2011 and November 2012.

Coumadin, also called warfarin, is a common blood thinner that is used to prevent blood clots after surgery