Women's risk of blood clots in the legs and lungs may be higher if they use the birth-control patch instead of the pill, FDA warns.

The Ortho-Evra EVRA (norelgestromin/ethinyl estradiol transdermal system) patch may carry an increased risk of blood clots, according to a study.

The U.S. Food and Drug Administration said it updated the label on the Ortho Evra birth-control patch to reflect the results of one study that found women using the patch faced twice the risk of clots than did women on the pill.

"Even though the results of the two studies are conflicting, the results of the second epidemiology study support FDA's concerns regarding the potential for Ortho Evra use to increase the risk of blood clots in some women," the FDA said in a notice published on its website.

Ortho-Evra contraceptive patch contains hormones similar to those in birth control pills. Initially the makers of the patch warned about serious risks, which can be life-threatening, including blood clots, stroke or heart attacks and are increased if a woman smokes cigarettes. Cigarette smoking increases the risk of serious cardiovascular side effects, especially in women over 35. Some women should not use the contraceptive patch, Johnson & Johnson Pharmaceutical Research & Development warned,including women who have blood clots, certain cancers, a history of heart attack or stroke, as well as those who are or may be pregnant.

Health Canada is currently reviewing information from the manufacturer to decide if birth-control patch labels should be changed in Canada. The review is expected to take one month.

The risk of clots in women using either the patch or pill is relatively small. Only six women out of 10,000 would develop clots in any given year, said Dr. Daniel Shames, of the FDA's Center for Drug Evaluation and Research. However, not a single woman would like to be among those unfortunate six, we assume.