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When should we use metformin in PCOS?

Q - Which women with PCOS should receive metformin?

A - There are now many studies supporting the view that metformin is useful treatment for improving the rate of ovulation and for hirsutism in polycystic ovary syndrome (PCOS). But there has been a relative paucity of randomised controlled trials (RCTs) to assess efficacy and those performed have included rather small numbers of subjects.

Despite the increasing popularity of metformin among both patients and doctors it is difficult to be clear about how effective it is (particularly in relation to more established therapies) and in which patients with PCOS such treatment is indicated.

The largest RCT published has 92 subjects. The most significant effect of treatment was an improvement in the rate of ovulation from 13 per cent of cycles during placebo treatment to 23 per cent in the metformin-treated group. The same group have, in a subsequent RCT, reported a reduction of hair growth in hirsute subjects treated with metformin.

The recent Cochrane Review of 13 RCTs supports the concept that metformin improves the frequency of ovulation, particularly when combined with the ovulation induction agent, clomiphene. There were insufficient data to comment confidently on the effects on hirsutism. Most of the published studies have included mainly women who are either overweight or obese and it remains unclear whether metformin is useful in lean subjects with PCOS.

I have some sympathy with their reservations that there are no data regarding safety of long-term use in young women and that metformin 'should be used as an adjuvant to general lifestyle improvements, and not as a replacement for increased exercise and improved diet'.

Stephen Franks, professor of reproductive endocrinology,

Institute of Reproductive and Developmental Biology, Hammersmith Hospital, London

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