Like most medicines, hormone therapy has benefits and risks.
If menopausal symptoms like hot flashes and vaginal dryness are disrupting your life, you may be considering hormone therapy. It's often the most effective treatment for these symptoms. And it has other benefits, like helping to keep bones strong as you age.
But there are risks, too, including a raised risk of certain kinds of cancer. That doesn't necessarily mean you have to avoid hormone therapy. But it's worth your time to understand what those risks are before you make a decision.
There are two basic kinds of menopausal hormone therapy—and the risks are different for each:
Estrogen-only therapy (ET). Estrogen is the hormone that eases menopausal symptoms most, but it can raise the risk of endometrial cancer (in the uterus). So doctors usually only prescribe ET if you've had a hysterectomy.
Estrogen-progestin therapy (EPT). This combines estrogen with progestin, a synthetic version of the hormone progesterone that helps lower the risk of endometrial cancer. It's more likely to be prescribed if you still have a uterus.
Hormone therapy can also be given several ways. If you receive it as a pill, patch or shot, the hormones will reach all parts of your body. This is called systemic therapy.
Alternatively, very small doses of hormones (usually just estrogen) can be placed inside the vagina to treat symptoms like dryness. This is called local therapy. And because it's a low dose, it may be given to women who still have a uterus.
What the science says
Two major studies sponsored by the National Institutes of Health as part of the Women's Health Initiative (WHI) give the most complete picture of how hormone therapy affects cancer risk. Each study tested hormone therapy against a placebo in thousands of healthy women past menopause.
From these and other studies, we've learned about the effects of ET and EPT on various kinds of cancer.
For women who take ET:
Breast cancer.Estrogen alone does not raise the risk of breast cancer. In fact, for some women, this therapy is protective. For example, it modestly cuts risk in those without a family history of breast cancer.
Colorectal cancer. ET doesn't appear to affect the risk of this cancer.
Endometrial cancer. When given as systemic therapy, ET raises the risk of endometrial cancer, which affects the lining of the uterus. That's why systemic ET is usually only prescribed for women who don't have a uterus. It's not yet clear if local ET therapy, which uses much smaller doses, has any effect on endometrial cancer risk.
Ovarian cancer. While the WHI studies couldn't draw any conclusions about ovarian cancer, another analysis of over 50 studies showed that ET raises the risk of ovarian cancer in women past menopause. But that risk drops when women stop using ET.
For women who take EPT:
Breast cancer. Women who take EPT are more prone to breast cancer—and their risk rises the longer they take it. Also, if breast cancer develops, women taking EPT tend to have more advanced tumors at diagnosis. However, the raised risk of breast cancer disappears within three years after EPT stops.
Colorectal cancer. The results are mixed: EPT appears to lower the risk of colorectal cancer. But if colorectal cancer occurs, it tends to be more advanced in women who take EPT.
Endometrial cancer. Progestin helps moderate the risk of endometrial cancer that is raised by estrogen alone. That's why doctors will most likely prescribe EPT for women who still have a uterus.
Lung cancer. While EPT doesn't add to the risk of getting lung cancer, it is associated with a higher chance of dying from lung cancer.
Ovarian cancer. The WHI studies couldn't find an increase in risk. But the analysis of the 50 studies mentioned above found that EPT also raises ovarian cancer risk in the same way that ET does.
What's your choice?
Deciding whether to take hormone therapy, what kind and for how long is a complex decision. So be sure to talk carefully about your options with your doctor.
Your doctor can also share information about how hormone therapy may affect your risk for other conditions, such as heart disease, stroke and blood clots.
Together, you can decide what's best for you.
Finally, if you decide that hormone therapy makes sense for you, here's a rule of thumb that can help minimize your risk: Take it at the lowest effective dose for the shortest possible time.
And check in regularly with your doctor. That way your doctor can keep a close eye on how effective your therapy is and watch for any side effects.