As with all drugs, there are risks associated with HRT. These include the possibilities of cancer of endometrium (lining of the womb), breast cancer, breast soreness, vaginal bleeding, high blood pressure and blood clots in the veins (venous thrombosis).
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HRT and high blood pressure
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 HRT and develop high blood pressure. This is rapidly reversed when HRT is stopped. It may also be possible to alter this effect by changing the dose and the way in which HRT is given.
HRT and blood clots
There is definite evidence to show that the oestrogen in oral HRT can cause an increased susceptibility to blood clot formation in the veins. This is the case whether or not a progestin is added. However, the risk is very small and there is no evidence that this increases the risk of death as a result of these clots. In fact, the risk is less than half of that during normal pregnancy.
Women who have already had thrombosis have an increased risk of suffering further clot formation if they take oestrogen orally. However, this seems to be diminished if they use transdermal formulations of HRT – only under close supervision though.
Vaginal bleeding and other problems with HRT
One of the biggest problems of HRT is the return of menstrual periods – that monthly nuisance, the loss of which is one of the best things about the menopause!
However, vaginal bleeding is only a symptom. The underlying cause may be genuine “menstruation” as a result of hormonal stimulation with subsequent shedding of the endometrium, like it is experienced with normal periods, or it might be due to local causes (for example vaginal sores), or there may be a developing cancer of the endometrium. The doctor will be able to differentiate between these causes. This is the reason why HRT should not be sold over-the-counter at any pharmacy but should be administered under a doctor’s supervision.
Breast tenderness and bloating are also possible problems, but these can often be dealt with by altering the dose.
There are forms of HRT available now which minimise or prevent vaginal bleeding altogether. However, the problem of unexpected bleeding while on HRT remains for most women and is something to consider when making the decision as to whether to use HRT at all.
Cancer of the endometrium and HRT
In the past, HRT was administered only as oestrogen with no addition of progestin, and a woman who still had her womb intact had the risk of developing cancer of the endometrium. This is because oestrogen causes an increased growth and cell production of the lining of the womb, which - if excessive - is called endometrial hyperplasia. Atypical cells may or may not be present during this process. If atypical cells are present, then there is a risk of cancer developing.
As such, women who took oestrogen alone, called unopposed oestrogen, had a risk of developing endometrial cancer of two to eight-fold higher than the general population. By adding progestin to the HRT regimen, this risk is prevented. Progestin is added to HRT in different time laps, either for half the cycle or continuously.
HRT regimens in which the addition of progestin is continuous, definitely do prevent endometrial hyperplasia. However, there are HRT regimens in which progestin is given for only 12 days of a cycle of continuous oestrogen therapy, the advantage being that some of the beneficial effects of oestrogens are not counteracted by progestins all the time.
Endometrial hyperplasia, if it develops, does seem to occur more often in women who are taking HRT this way. This suggests that continuous combined oestrogen and progestin is the only truly effective form of oestrogen delivery which will prevent endometrial hyperplasia, and so decrease the risk of endometrial cancer.
The fact that there are several types of HRT regimens available is based on the different individual responses. If all peri- and postmenopausal women were the same, there possibly would be only one form of HRT. The doctor will assess the individual response pattern in order to prescribe the appropriate form of HRT. In women who had a hysterectomy (removal of the womb), the prescription of HRT is generally easier. There is no risk of getting endometrial cancer, and oestrogen without progestins can be administered. This is also called ERT (“Estrogen” Replacement Therapy).
The continuing controversy of breast cancer and HRT
Is there an increased risk of breast cancer in women who take HRT? At present there is no definite answer to this. Earlier studies suggested that women who take HRT have a slightly greater risk of breast cancer relative to women who are not using oestrogen.
Some of the most recent research – looking at many different studies which have been done – have come up with a figure of a 2.3% increase in the risk of breast cancer with each year of HRT use. This levels off after stopping HRT. How this affects women with a family history of breast cancer is still unclear.
It has to be remembered that there are several possible risk factors for developing malignancies in any case, and these have to be taken into consideration when evaluating the risk of breast cancer associated with HRT in a particular woman.
Recent research suggests that short-term use of HRT (less than five years) is not associated with an increase in the risk of breast cancer, but that using it for more than ten years may be.
However, deaths from breast cancer have not been shown to increase in women using oestrogen. In fact, there may be fewer deaths among women using oestrogen. Breast cancer seems to be detected earlier in women who are on HRT, probably because they are specifically worried about the disease and are followed up regularly by their doctors.
The current consensus is that there is some increased risk of breast cancer associated with HRT. However, this risk varies widely among women, so individual risk factors need to be evaluated before starting HRT. It is also worth remembering that deaths from coronary artery disease among women outnumber deaths from breast cancer. So the relative risk of both conditions needs to be assessed as well.
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