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 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.