About 5% of women using oral contraceptives develop high blood pressure for reasons which are not clear. Oestrogen usually causes no changes in blood pressure. In fact, in some women it lowers blood pressure.

However, some women have an unusual reaction to the oestrogen in HT and develop high blood pressure. This is rapidly reversed when HT is stopped. It may also be possible to alter this effect by changing the dose and the way in which HT is given.

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Self-monitoring at home