(HealthDay News) - - The U.S. Food and Drug Administration said Wednesday that it has updated the label on the Ortho Evra birth-control patch, warning that some women who use the product face a higher risk of blood clots.

The label revision came after the final results of a study, commissioned by the drug's maker, Johnson and Johnson, found that users face twice the risk of clots in the legs and lungs than women taking traditional birth-control pills.

But a second study, also commissioned by Johnson and Johnson, found no difference in risk between the patch and 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 statement on its Web site.

"Blood clots occurring in the legs or lungs are serious and rare events that are a potential risk for all hormonal contraceptive therapies," Dr. Daniel Shames, the acting deputy director of FDA's Office of Drug Evaluation in the Center for Drug Evaluation and Research, told a press conference.

Risk factors for blood clots associated with contraceptives include smoking, obesity, inactivity, surgery and high doses, Shames said.

The FDA has also asked Johnson and Johnson for a longer follow-up of women using the patch to look for cases of blood clots, heart attack and stroke.

Right now, the FDA believes the patch is safe for most women. "Ortho Evra risk profile is acceptable for a highly effective contraceptive," Shames said.

However, the FDA said it remains concerned about the potential risk of blood clots in some women.

The label change contains some information previously reported by Johnson and Johnson in a Feb. 16, 2006, press release. That information was based, in part, on an interim report from one of the two studies. The label change announced Wednesday is based on the latest results from the two studies, the FDA said.

The label change includes a warning that women using the weekly patch -- the only birth-control patch approved by the FDA -- receive substantially more estrogen than women taking a daily birth-control pill. The pills typically contain 35 micrograms of estrogen.

Higher levels of estrogen may put some women at increased risk of blood clots. The FDA is urging women to talk to their doctors to see if the patch is appropriate for them.

"When the patch came out, I enthusiastically used [it] in women who don't like to take pills," said Dr. Steven R. Goldstein, a professor of obstetrics and gynecology at New York University School of Medicine. "But I thought that there was too much estrogen in it, because four of the women lasted one or two months and complained of symptoms, which are usually attributed to excess estrogen."

"My advice is that for a patient who had been on the patch for any period of time and is doing well, I don't see a need to take her off," Goldstein added. "With most of the estrogen-related blood clots, the risk is greatest in the first six months of use."