WASHINGTON: Birth control drugs that were heavily promoted as having fewer side effects and the ability to clear up acne and other hormonal bothers are under new scrutiny from US safety regulators.

Research suggesting that newer birth control formulations are more likely to cause blood clots than older drugs has prompted the Food and Drug Administration to consider new safety measures in meetings later this week. The increased risk is slight, but significant because blood clots can cause heart attacks, strokes and blockages in lungs or blood vessels, which can be fatal.

Regulators could order new warning labels on several contraceptives that gained popularity in the last decade, including Bayer's pill Yaz, which was the best-selling birth control pill in the US for 2008 and 2009.

Yaz, its Bayer precursor Yasmin, and similar drugs use a version of a female hormone that appears to reduce side effects found in older drugs, including bloating and mood swings.

On Tuesday, a judge unsealed several court documents suggesting Bayer may have withheld data from the FDA about the blood clot risks of its drugs. The documents stem from expert opinion gathered by personal injury lawyers suing Bayer on behalf of patients.

A Bayer spokeswoman said the company had no comment on the material in the documents, noting the issues would be addressed at trial.

Bayer AG spent more than $270 million on TV and magazine advertisements for Yaz between 2007 and 2010, according TNS Media Intelligence. Such big-budget campaigns are rare for birth control products. One advertisement featured young women singing the Twisted Sister anthem, ''We're Not Gonna Take It,'' while popping balloons labeled ''moodiness,'' ''bloating'' and ''acne.''

Sales of Yaz have fallen since regulators forced Bayer to correct advertisements that overstated Yaz's benefits and as safety questions drew scrutiny in both the US and Europe.