About a year ago, I started taking birth control pills and my doctor explained that the worst side effect is blood clots. However, she never fully explained what to expect if I experienced a clot. When I got a cramp in my calf and thought it was a clot, my doctor said I shouldn't be paranoid. After that event, I stopped taking the Pill and haven't visited my doctor since. I'd like to go back on the Pill but would like to know more about the warning signs of blood clots, if they're common and who is at risk.

--Frances

The risk of developing blood clots as a consequence of oral contraceptive use is very, very small -- UNLESS you are over 35 and a smoker, or you have some underlying blood-clotting disorder. Most blood clots develop in the veins in the leg, producing calf pain or other leg pain. This is persistent and is different from the calf spasms that many people get while sleeping. The area overlying the clot will be tender to the touch and often warm and red. The leg may be swollen. Development of these symptoms, regardless of pill use or not, warrants an immediate visit to your doctor.

If a clot is suspected, often an ultrasound-type test will be done to assess blood flow; sometimes venography (injecting dye into the venous system) is necessary. Treatment consists of blood thinners, initially through an intravenous (IV) line and then by pills. If a clot develops while you are on the pill, you should stop using it and never use it again.