When should metformin be added in infertile women with PCOS?

[Verified against the International Guideline for PMOS (formerly PCOS)] For anovulatory infertility specifically, metformin sits third in the hierarchy, not first. Metformin could be used alone in women with PMOS/PCOS with anovulatory infertility and no other infertility factors, to improve clinical pregnancy and live birth rates — whilst informing women that there are more effective ovulation agents (evidence-based recommendation, 5.4.1.1). That final clause is the recommendation's own wording and should be reflected in consent. Offering metformin without saying more effective options exist is not consistent with the guideline. Clomiphene citrate could be used in preference to metformin to improve ovulation, clinical pregnancy and live birth rates (evidence-based recommendation, 5.4.2.1). And letrozole is first-line ahead of both. Practice points that shape where metformin does make sense: Counsel on potential mild gastrointestinal side effects (5.4.1.2). Healthcare and resource burden — monitoring, travel and costs — are LOWER with metformin (5.4.1.3). For a patient facing distance, cost or monitoring access constraints, that is a legitimate reason to choose a less effective agent, and the guideline names it explicitly. Age and screening for other fertility factors need to be discussed before prescribing metformin (5.4.1.4). In an older woman, choosing the lower-burden but less effective option carries a time cost that may outweigh the convenience. Note this addresses metformin for anovulatory infertility. Its role in metabolic management of PMOS, and in pregnancy for women with PMOS, are separate questions.