The Medication Interaction With Metformin Women Should Be Mindful Of

Metformin is one of the most common medications used to lower blood sugar in people with type 2 diabetes. It works by limiting the amount of glucose your liver releases and helping your cells use more glucose from your blood for energy. Unlike insulin, which can sometimes lead to weight gain, metformin usually doesn't have that effect. In fact, some people even lose a little weight while taking it. Another plus is that metformin comes in pill form, while insulin and GLP-1 drugs are taken as injections.

Like any medication, metformin can interact with other drugs you might be taking. Women who take hormonal birth control or estrogen medications should check with their doctor while on metformin. While metformin itself doesn't interfere with birth control, those hormone medications may reduce metformin's effectiveness, which could cause blood sugar levels to rise. If you notice symptoms of high blood sugar, such as excessive thirst or urinating more often, your doctor might need to increase the strength of your metformin to control your blood sugar. However, metformin might be beneficial for some women who may have hormone-sensitive conditions and risk factors.

Although estrogen plays an important role in regulating the female reproductive system, maintaining healthy cholesterol and blood sugar levels, and supporting brain function, the National Cancer Institute says that higher and long-term estrogen exposure is associated with an increased risk of certain cancers, particularly when some types of hormone therapy are used.

A 2020 study in the Journal of the National Cancer Institute explored whether metformin could influence estrogen levels and potentially lower the risk of hormone-related breast cancers. The researchers studied postmenopausal women with non-hormonal (estrogen receptor–negative) breast cancer who were randomly assigned to take either metformin or a placebo for six months.

(Here are some tips to improve your breast health.)

The women who received metformin showed a significant decrease in estradiol, the most potent form of estrogen found in the body. Although this reduction would not directly help women with non-hormonal breast cancer, the finding suggests that metformin could help lower the risk of estrogen-dependent cancers, such as hormone receptor–positive breast cancer or endometrial cancer. By reducing circulating estrogen, metformin might add another layer of protection against the growth of these hormone-driven tumors.

Metformin may also help manage hormonal conditions such as polycystic ovary syndrome (PCOS). Women with PCOS have higher levels of the androgen hormone and often experience symptoms, such as heavy or painful periods, excess body hair, weight gain, acne, or thinning hair. Treatment for PCOS often includes birth control pills to reduce androgen levels and regulate menstrual cycles. Some women with PCOS are at higher risk of developing long-term health problems such as type 2 diabetes and cardiovascular disease.

(Here are foods to eat and avoid if you have PCOS.)

A 2011 study in Fertility and Sterility tested how taking metformin along with an oral contraceptive affected overweight and obese women with PCOS compared to taking an oral contraceptive with a placebo. After three months, the women who took metformin showed better blood vessel function, lower androgen levels, and a small but significant decrease in body weight. The study suggested that adding metformin to oral contraceptive therapy may improve vascular health and hormone balance in women with PCOS.