How does metformin for PCOS work?

PCOS can involve insulin resistance, meaning the body needs more insulin to help move glucose into cells. Higher insulin levels can affect ovarian hormone signalling and make ovulation less predictable. Metformin helps the body respond to insulin more effectively and reduces glucose production by the liver. This may help hormone patterns settle, although the effect differs between individuals.

Metformin is not a hormone and does not remove ovarian cysts. It may help with irregular ovulation and cycle patterns, but it is not the only treatment for PCOS. Some people need a separate approach for pregnancy planning, unwanted hair growth, acne or protection of the womb lining.

Take it with food and follow the prescribed schedule. Starting with a lower dose or increasing gradually may make stomach upset easier to manage. Nausea, loose stools, abdominal discomfort and reduced appetite can occur, especially early in treatment. Do not change the dose or stop suddenly without discussing it with your prescriber. Tell them about kidney, liver or digestive problems and all medicines or supplements you use.

For background, see [Metformin for PCOS](/treatments/medical-gynaecology/metformin-for-pcos/), [Polycystic Ovary Syndrome](/conditions/polycystic-ovary-syndrome/) and [Metformin](/materials/metformin/). [Irregular Periods](/symptoms/irregular-periods/) may have causes other than PCOS.

Contact your clinician if vomiting or diarrhoea prevents you from keeping fluids down, digestive symptoms are severe, or side effects do not settle. Seek urgent help for marked weakness, fast breathing, confusion or severe illness, particularly if you are dehydrated or have kidney problems. Tell your clinician promptly if pregnancy is possible, periods stop for a prolonged time, or you develop unusual bleeding.

Ask what goal the medicine has for you, how the dose will change, when to review cycle or ovulation patterns, and whether blood tests are needed. If you are trying to conceive, ask how metformin fits with fertility treatment and pregnancy planning.