If you’re a woman, you might use an oral contraceptive for birth control…or for another reason, such as heavy periods, acne or premenstrual dysphoric disorder (PMDD), which involves having symptoms of depression, irritability and tension before menstruation.

Whatever the reason, it’s been hammered into the heads of women—many birth control medications may slightly raise your risk for blood clots.

These clots can occur in any artery or vein in the body. Sometimes they dissolve and cause no problems, but other times—depending on where they occur—they can cause life-threatening problems, such as pulmonary embolism (blocked blood flow to the lungs), ischemic stroke (blocked blood flow to the brain) or angina (blocked blood flow to the heart).

Recently, the FDA announced that certain birth control pills may raise that risk more than other types of birth control pills—and will require new labels.

So which pills are the culprits?

And what should you do if you’re taking one of them?

I posed these questions, as well as others, to Margaret Polaneczky, MD, associate professor of clinical obstetrics and gynecology at Weill Cornell Medical College in New York City.

If you or a loved one happens to be taking one of the pills in question, then you’ll definitely want to hear what she has to say…

SOME PILLS ARE RISKIER THAN OTHERS

Dr. Polaneczky explained that the FDA based its recent decision on large studies that were released last year. These studies revealed that birth control pills containing a synthetic form of progesterone known as drospirenone may create up to three times as much risk for blood clots as birth control pills containing other types of progesterone. Brands that contain drospirenone include the popular Yaz and Yasmin, as well as Beyaz, Gianvi, Loryna, Ocella, Safyral, Syeda and Zarah.

It’s important to note that these are not the only types of birth control that have been linked to higher risks for clots. Dr. Polaneczky noted that in the late 1990s, the FDA found a similarly increased risk for clots from birth control pills containing desogestrel (the brands Desogen, Mircette and their generics), and that last year the FDA announced that the Ortho Evra patch could create higher clot risks than low-dose oral contraceptive pills. And though the FDA hasn’t formally addressed this yet, recent research suggests that the NuvaRing (a vaginal insert) may also raise the risk for clots more than other types of birth control.

When you look at all the findings, she said, they suggest that the lowest clot risk might be found in older birth control pills containing levonorgestrel or norethindrone and newer birth control pills containing norgestimate.

WHY THE DIFFERENCE IN RISK?

It’s maddening when drugs are approved by the FDA and then later discovered to be riskier than previously thought. Why didn’t we know about this danger sooner? “Before drugs are approved by the FDA, they are tested in clinical trials. And clinical trials may be too small to detect a statistically significant increase in clots. It’s often only when a drug makes it out into the general population of millions of women that an increased clot risk becomes evident,” Dr. Polaneczky said.

Right now, she added, we don’t know why this particular form of progesterone increases clot risk even more. So what should you do if you’re on one of these drospirenone-containing pills?

PUT THE RISK IN PERSPECTIVE

The first thing to remember, said Dr. Polaneczky, is that there’s a difference between relative risk and absolute risk. The relative risk of these brands may be higher when compared with that of other pills. But the risk for blood clot is very low to start with, so even when that risk is raised, the absolute risk is still very low.

If 10,000 women took birth control pills that didn’t contain drospirenone for one year, three would be likely to develop clots caused by the pills…and if 10,000 women took pills that did contain drospirenone for a year, nine would be likely to develop clots caused by the pills.

But keep in mind, Dr. Polaneczky said, that if you’ve been taking one of the brands listed above for more than one year, you’re already at a lower risk for clotting, since most pill-caused clots occur in the first year of use.

If you took a pill that contains drospirenone and then stopped and are now taking it again, there’s a chance that your risk might be as elevated as it would be during your first year taking it, said Dr. Polaneczky, so talk to your doctor about your specific risks.

WHAT YOU CAN DO ABOUT IT

If you use any of the brands mentioned earlier, talk to your doctor, said Dr. Polaneczky, who added that the decision may be different for each woman. For example, if you’re taking the pill for only birth control and you tolerate other types of birth control pills that don’t contain drospirenone, then it might make sense to switch, she said. But beyond clot risk, each type of birth control pill has its own set of risks and side effects. If you use the pill to treat PMDD and it’s the only one that provides relief for you and/or it’s the only one that doesn’t trigger side effects, then perhaps it’s worth accepting the increased blood clot risk.

I asked Dr. Polaneczky what all women—especially those taking the brands mentioned earlier—can do to lower their clot risk. On long car trips or flights (or when you’re at a desk for many hours), avoid crossing your legs, do calf raises (lift your heels as high as you can, hold for two seconds and then repeat 10 times), walk around periodically and stay hydrated.