Advice
Intervention and alternatives
Metformin reduces glucose production in the liver and improves the insulin sensitivity of other cells.
Condition
PCOS is characterised by irregular menstrual cycles, infertility, hirsutism and acne. It is the most common condition affecting the endocrine system among women (Costello et al. 2007). Women with PCOS have an increased risk of developing type 2 diabetes compared with women of similar age and weight, and are also thought to be at increased risk for endometrial cancer (Costello et al. 2007).
The exact cause of PCOS is unknown. Insulin resistance (reduced glucose response to a given amount of insulin) is present in 65–70% of all women with PCOS (Marshall and Dunaif 2012), with consequent compensatory hyperinsulinaemia. Hyperinsulinaemia directly stimulates both ovarian and adrenal androgen secretion and suppresses liver sex hormone-binding globulin synthesis, resulting in an increase in free, biologically active androgens. This causes premature follicular atresia and anovulation along with the other clinical manifestations of hyperandrogenism such as hirsutism and acne (Costello et al. 2007).
Alternative treatment options
No studies compared metformin to placebo. The most common comparator to metformin in the studies identified for this evidence summary was co-cyprindiol (ethinylestradiol 35 micrograms plus cyproterone 2 mg) alone. A small number of studies compared metformin with metformin plus co-cyprindiol. Although co-cyprindiol also acts as an oral contraceptive, the summary of product characteristics states that it is not indicated for women solely for contraception, but should be reserved for those women needing treatment for the androgen-dependent conditions for which it is indicated: severe acne and moderately severe hirsutism. Low-dose oral contraceptives can also be prescribed to help regulate the menstrual cycle and are licensed for oral contraception but not for PCOS (British National Formulary, December 2012).
Other treatments for the symptoms of PCOS include weight loss, cholesterol-lowering medication and acne medication. Additional treatments are available for women with PCOS who are trying to conceive but these are outside the scope of this evidence summary.