While birth control pills are highly reliable in preventing pregnancy, there is the possibility that you could become pregnant. This is especially true if you miss a dose or do not take the pills regularly. Being overweight or obese may also increase your risk of pregancy. The excess weight may affect how well the pills work in your body.

Oral contraceptive pills can increase your risk of developing blood clots in the veins in your legs. These can become life threatening if the blood clots leave your legs and travel into you lungs. The risk of blood clots is increased more in people who smoke.

There are different kinds of birth control pills. Some are combination pills, with estrogen and progestin, while others are "mini-pills" with just progestin. Estrogen may affect triglyceride levels and total cholesterol levels—increasing HDL "good" cholesterol and decreasing LDL "bad" cholesterol. Progestin, though, may cause "good" cholesterol to lower and "bad" cholestorol to rise. But, for most women, these changes in blood levels are not strong enough to have a poor effect on your health.

Taking birth control pills may increase the risk of high blood pressure. This risk may be greater if you have other conditions, like being overweight, having a family history of high blood pressure, or smoking. If you take birth control pills, your doctor will check your blood pressure. If you already have high blood pressure, talk to your doctor about other contraceptive options.

Women aged 35 or older who smoke heavily and take birth control pills have an increased risk of having a heart attack or stroke. You may have an even greater risk if you have other risk factors (eg, family history of cardiovascular disease, high cholesterol, high blood pressure). If you want to take birth control pills, you should first quit smoking, since smoking increases your chance of developing many other health problems.

Taking birth control pills for many years may increase the risk of certain types of cancer, like cervical cancer. Researchers are still investigating the link between birth control pills and breast cancer. Some studies have found that there is an increased risk, while others studies have come to the opposite conclusion. According to the National Cancer Institute, there appears to be a slight increase in risk, but the risk level goes back to normal after 10 years of stopping birth control pills. It is important to remember that there are many other risk factors for cancer. If you are at high risk for breast cancer (eg, having certain types of genes or a family history) or other types of cancer, talk to you doctor about the best contraceptive for you.

While the pill may increase the risk of some types of cancer, it can also decrease the risk of other types of cancer, like ovarian and endometrial cancer. Studies have found that the more years a woman takes the pill, the better her protection. In addition, researchers are investigating whether birth control pills decrease the chance of developing colorectal cancer.

Taking birth control pills may reduce your risk of:

• Heavy bleeding, irregular periods, painful periods, and menstrual cramps
• Ectopic pregnancy (a pregnancy that occurs outside the uterus, particularly in the fallopian tubes)
• Iron-deficiency anemia
• Acne
• Unwanted hair growth
• Pelvic pain due to endometriosis
• Pelvic inflammatory disease

There are many different types of birth control pills on the market. You and your doctor can decide which kind is best for you, or if a different contraceptive option would be a better choice. Just keep in mind that the pill does not protect against HIV and other sexually transmitted diseases.