Do oral contraceptives raise blood pressure?

Soon after oral contraceptives were first introduced, more than 30 years ago, there were a number of reports of high blood pressure associated with their use. The pills contain a mixture of estrogens and progestins, but the amount of each ingredient in the preparations used today is only about one fifth of the original dose, although there is considerable variation between different brands. The Nurses’ Health Study has investigated the risk of developing high blood pressure from taking the oral contraceptives now in use. The study followed the health of more than 100,000 American nurses, who were first contacted in 1989. Among other questions, they were asked about their use of oral contraceptives and their blood pressure on three occasions over a four year period. Those who reported having hypertension at the beginning of the study were excluded from this analysis. The principal findings were:

• The chances of developing hypertension were about 80% higher in the women who had used oral contraceptives in comparison with those who had not.
• The risk was slightly higher in women who had used them for more than six years. The risk did not vary significantly according to the amount of estrogens and progestins in the pills.
• Women with a family history of high blood pressure were at increased risk of developing it themselves, but they did not appear to be any more susceptible to the effects of oral contraceptives than those with no family history.
• There was no evidence of any racial difference in susceptibility to the effects of oral contraceptives on blood pressure; if anything, black women were at lower risk than white women.
• The number of women who were estimated to have developed hypertension as a result of taking the pills was small- the equivalent of 41 cases in 10,000 women over a period of one year, or 0.4%.

Doctor’s comments

This study is reassuring for women taking oral contraceptives, because although there is a definite risk of developing high blood pressure, it is quite small. Furthermore, other studies have shown that if the pressure does go up, it will usually go back to its previous level within three months of stopping the pills. One implication is that if you are taking oral contraceptives, it is important to get your blood pressure checked at regular intervals. Women who already have hypertension are generally advised not to take oral contraceptives.