Drug labelling for oral contraceptives containing drospirenone, sold under the brand names Yasmin and Yaz, should be updated to emphasize recent data suggesting a higher risk of blood clots with these drugs than older birth control pills, U.S. federal health experts say.

The Food and Drug Administration's panel of experts voted 21-5 Thursday that labelling on the popular drugs made by Bayer is inadequate and needs more information about the potential risk of blood clots in the legs and lungs.

Health Canada had asked Bayer to change the labels on the two brands after it concluded use of the medications is linked to higher rates of blood clots than seen with older brands of the pill.

Health Canada began the review earlier in the year after the British medical journal BMJ published studies that raised safety concerns about birth control formulations that contain the lab-made hormone called drospirenone, which mimics the naturally occurring female hormone progesterone. Yasmin and Yaz are the only oral contraceptives containing drospirenone that are sold in Canada.

On Monday, Health Canada issued a statement saying that its review of safety data for the drugs suggests women using them may be at a 1.5-to-three fold increased risk of experiencing a clot compared to women using other birth control drugs.

The department said the labels for the two drugs have been updated to reflect the increased risk.

Approved in 2006, Yaz grew into the best-selling birth control pill in the U.S. by 2008, backed by hundreds of millions of dollars in TV and magazine advertising that emphasized its ability to clear up acne and other hormonal side effects. But prescriptions have fallen more than 80 per cent in the last two years amid safety concerns.

While the FDA group disagreed on the quality of the evidence concerning the higher risk of users developing blood clots with the newer drugs, the overwhelming majority said it should be clearly stated in the label, including the potentially fatal nature of blood clots.

"Clearly the wording is inadequate and incomplete," said Dr. Richard Bockman of New York's Hospital for Special Surgery. "Adverse events have to be made graphic so physicians and patients are aware of the consequences."

In an earlier vote, panellists voted 15-11 that the pills remain a beneficial option for preventing pregnancy. The majority ruling amounts to a vote of confidence for keeping the drugs on the market, though well over a third of panelists voted against the drug's overall benefit, citing numerous alternatives available.

"I can see no real group of patients that this drug benefited over existing alternatives," said Mark Woods of New York University School of Medicine. "Without any clear benefit, and given the potentially catastrophic risk, I voted no."

Two large studies conducted by German drugmaker Bayer have shown no difference in blood clots between patients taking the company's drugs and patients taking older medications.

But since 2009, five large studies have suggested drospirenone-containing pills carry a slightly higher risk of blood clots than older birth control pills, though events in both groups are very rare. Even a slightly higher risk can be critical because blood clots can trigger heart attacks, strokes and blockages in lungs or blood vessels.

The most recent study by the FDA found women taking Yasmin had a 75 per cent higher chance of suffering a blood clot than patients taking a combination of older drugs. The absolute risk of a blood clot is still far less than a fraction of a per cent.

Studies missing numbers on weight, smoking

FDA scientists noted shortcomings with all the recent studies of Yaz and Yasmin, including missing information about patient weight and smoking status, which can increase the risk of blood clots. While not definitive, panellists said the information should be explained clearly in the labelling for physicians and patients.

"I think we can do a much better job than labels I have seen," said Dr. Valerie Montgomery Rice, of the Morehouse School of Medicine.

Panelists said future studies must take into account patients' lifestyle, race and family history to accurately capture blood clot risk.

Earlier in the day, panelists heard more than a half-dozen patients or their family members who blame Yaz or Yasmin for sometimes deadly blood clots.

Blood clot kills woman, 20, panel told

Cindy Rippee spoke about her last conversation with her 20-year-old daughter Elizabeth Rippee, who died Christmas Eve 2008 when a blood clot travelled to her lung. Rippee said her daughter had been taking Yasmin for about two months, after taking another birth control pill, Tri-Sprintec, for a year previously.

"My daughter was a very smart young woman. If Elizabeth had been clearly told that Yasmin had more risk, maybe twice as much risk, as other pills she never would have switched to Yasmin and would be here today," said Rippee, of Escondido, Calif.

Rippee is among 4,000 to 6,000 plaintiffs suing Bayer in personal injury lawsuits pending throughout the U.S. court system.

Yaz and other drospirenone-containing pills accounted for 16 per cent of the hormonal contraceptives used in the U.S. last year, behind Warner Chilcott's Loestren, Johnson & Johnson's Ortho Tri-Cyclen and several other oral contraceptives.

The FDA has not set a timetable for any changes in Yaz's labelling. For now, many doctors say they don't expect to stop prescribing the drugs anytime soon. They point out that the risk of blood clots with any birth control pill is still far lower than that associated with pregnancy and birth, when surging hormone levels and reduced blood flow dramatically increase the chances of clotting.

Studies suggest that 10 in 10,000 women taking the newer birth control pills will experience a blood clot, compared with 20 in 10,000 women who are pregnant or have just given birth.

With files from The Canadian Press