Metformin and PCOS/PMOS: What Does It Do?

Why Is Metformin Prescribed?

Metformin is a prescription medication most commonly used to manage type 2 diabetes. It is also used in PCOS/PMOS, although this use may be off-label depending on the country.

Insulin resistance can occur in PCOS/PMOS, including in people who do not have a higher body weight. When insulin levels are elevated, this can contribute to excess androgen production in some people. Metformin helps the body manage glucose and can improve certain metabolic measures.

However, insulin resistance is not the only factor involved in PCOS/PMOS, and metformin is not necessary or appropriate for everyone.

How Does Metformin Work?

Metformin primarily reduces the amount of glucose released by the liver and improves the body’s handling of glucose. Its effects involve several biological pathways, rather than one single mechanism.

For some people with PCOS/PMOS, treatment may help improve insulin-related measures, blood glucose, lipid levels and aspects of hormonal health.

What does the newer evidence tell us?

A 2025 systematic review and meta-analysis reported improvements in measures such as fasting insulin, insulin resistance and testosterone, although responses varied across studies and participants. A 2024 systematic review of insulin-sensitising medicines also found metabolic benefits, but reproductive outcomes were less well established.

A 2026 meta-analysis of 51 randomised controlled trials found no significant overall effect of metformin on circulating LH or FSH levels. This is a useful reminder that its hormonal effects are not uniform and cannot be reduced to a simple promise of hormonal balance.

Metformin may help some people experience more regular menstrual cycles, but it does not guarantee that ovulation will return within three to six months. If pregnancy is the goal, a clinician can discuss fertility treatments with stronger evidence for inducing ovulation.

Side Effects and What to Know

Digestive symptoms: Nausea, diarrhoea, abdominal discomfort and other gastrointestinal effects are common, particularly when starting treatment or increasing the dose. Taking metformin with food, starting at a low dose and increasing gradually under medical guidance may help. Extended-release formulations may also be easier to tolerate for some people.

Vitamin B12: Long-term use can lower vitamin B12 levels. Your clinician may recommend testing, especially if you have risk factors or symptoms of deficiency.

How to take it: Follow the instructions for your specific prescription and formulation. Do not change your dose or switch formulations without speaking to your prescriber.

A Practical Tip

If digestive symptoms occur, make a note of when they happen, your prescribed dose and whether you took the medication with food. Share persistent or troublesome symptoms with your healthcare professional rather than stopping treatment or changing your dose on your own.

Your HeyTimi Action

If you use metformin, record your medication and any symptoms using HeyTimi’s existing medication and symptom logs. Over time, these notes can help you prepare specific questions for your clinician.

Remember, a change in symptoms or cycle patterns alone cannot confirm that insulin resistance or other metabolic markers have improved. Appropriate clinical assessments and laboratory tests may be needed.

References

1. Kelly FA, et al. (2025). Comparison of metformin with inositol versus metformin alone in women with polycystic ovary syndrome: a systematic review and meta-analysis of randomized controlled trials. Endocrine.
2. (2024). Impact of insulin sensitization on metabolic and fertility outcomes in women with polycystic ovary syndrome and overweight or obesity: A systematic review, meta-analysis, and meta-regression. Obesity Reviews.
3. Krysiak R, Simental-Mendía M, Simental-Mendía LE. (2026). Effect of Metformin Treatment on Gonadotropin Levels in Women With Polycystic Ovary Syndrome: A Systematic Review and Meta-Analysis of 51 Randomised Controlled Trials. Diabetes, Obesity and Metabolism.
4. Teede HJ, et al. (2023). Recommendations From the International Evidence-based Guideline for the Assessment and Management of Polycystic Ovary Syndrome. Journal of Clinical Endocrinology & Metabolism. This remains an important clinical guideline; it is not a newly published 2026 guideline. Read the guideline

Educational content only. This lesson does not replace individual medical advice or prescribe treatment.