Clots can form in the brain, eyes, lungs, heart, arms or legs. If the clot is in a blood vessel leading to an arm or leg, it can result in damage or even loss of a limb. The risk of blood clotting in a limb is three times higher for pill users than for non-users; about half this risk for the lower dose pills. If you have varicose veins, this does not increase your risk of this complication. However, smoking will definitely increase your risk of blood clotting.

If a clot forms in the legs or pelvis and breaks off and travels to the lungs, this results in a pulmonary embolus, which can be a life-threatening emergency. The risk of this happening is four times higher in pill users than in non-users (again less for lower dose pills).

For women on the higher dose pills, this risk of blood clots to the lungs was significant enough that women planning to have major surgery were advised to discontinue the pill four to six weeks prior to surgery and not restart until two weeks after surgery. It is unclear whether or not similar advice should be given to women on the lower dose pill.

If the clot is in a blood vessel to the heart, then a heart attack may result. Users of the high dose pills have double the chance of heart attacks as non-users. The risk of heart attack increases with age and heavy smoking. Pill users who smoke are about ten times more likely to have a heart attack than non-users who do not smoke. Women over 35 who smoke should choose another form of birth control.

Heart attacks and strokes are normally very rare for women under 50. The 1985 government report on the birth control pill cites research that says that women who have ever used the higher dose pill continue to experience a higher risk of heart disease than women who have never used the birth control pill. This means even if you stopped using the high dose pill, you may be four times as likely to die from heart disease as someone who has never used the pill. This finding has recently been disputed, with new analyses of the old studies.

According to Dr. Stanley Brown, Associate Professor of Gynecology at Western University in London, Ontario, (Treating the Female Patient, Sept/92) previous research was re-analyzed and showed that the death rate from heart disease was significantly increased only in women over 35 who smoked, or who had other independent risk factors, such as high cholesterol or diabetes.

If a blood clot to the brain develops, a stroke may develop. The risks of strokes in women who used the high dose pill is significantly higher than for non-pill-users and this risk is further increased by smoking. Just as for heart attacks, the risk of strokes was reported as being higher for women who have ever used the higher dose pill compared to those that haven't.

Studies have shown that women taking the high dose pill are twice as likely as non-users to have a rupture of a blood vessel in the brain.

The Pill And High Blood Pressure

Blood pressure is very slightly increased in all women on the pill. A small percentage of women develop a marked increase in blood pressure, which usually goes back to normal within three months after the pill is discontinued.

According to Dr. Wilfred Steinberg, Director of the Women's Health Center at St. Michael's Hospital in Toronto (Diagnosis, July/87), studies published in 1982 linked progesterone to the development of high blood pressure and changes in blood lipids. "In some cases," says Dr.Steinberg, "these changes were dose related; in others, changes in lipid profile seemed related to a specific progesterone."

Effects Of Pills On Blood Lipids (fats)

The pill increases the amount of fatty substances in the blood.

Estrogen causes a mild rise in cholesterol and a moderate rise in triglycerides in the blood; while progesterone causes a rise in cholesterol and no change or a fall in triglyceride levels. What this adds up to in terms of contributing to the risk of hardening of the arteries is not known, but it is thought that the estrogen and progesterone risk cancel each other out.

Experts believe, but have no proof, that the combined effect of estrogen and progesterone is to protect against heart disease.