I have PCOS and I’m confused about Metformin..

Written by: Mr Mahantesh Karoshi
Edited by: Cameron Gibson-Watt

The most common medication used in women with polycystic ovary syndrome (PCOS) is the insulin-sensitizer Metformin.


For women with PCOS, their bodies are producing more male hormones, which can result in irregular menstrual cycles, or may even stop menstruation altogether. Metformin treatment, however, can lower insulin and blood sugar levels in women with PCOS, stimulating ovulation and encouraging regular monthly periods.



For many women though, knowing its side-effects and how much it contributes to weight loss can be quite confusing. One of our top consultant gynaecologists and experts in women’s health, Mr Mahantesh Karoshi, clears this all up for us.


Fast facts

  • Women with PCOS are commonly insulin resistant, meaning their bodies can make insulin but can't use it effectively, which increases their risk for type 2 diabetes.
  • More than half of women with PCOS will develop type 2 diabetes by the age of 40 if they have weight issues.
  • Women with PCOS are more insulin resistant than weight-matched women who do not have the syndrome.
  • Insulin resistance is seen in approximately 10% of slim and 40% of obese women with PCOS.
  • The more the overweight an individual is the greater the degree of insulin resistance.
  • Maternal weight can have a profound effect on both natural and assisted conception, influencing the chance of becoming pregnant and the likelihood of a healthy pregnancy.


Insulin resistance

As a result of insulin resistance in PCOS, circulating insulin levels rise. In the ovaries, high levels of circulating insulin can contribute to excess male hormone production and the absence of ovulation. Simple screening tests, such as fasting blood glucose, can help rule out the presence of insulin resistance if it is less than 5.2 mmol/l.


What does Metformin do for PCOS?

Metformin enhances the sensitivity of insulin. Hence, it is logical to anticipate that insulin lowering and sensitising treatments, such as Metformin, can improve symptoms and reproductive outcomes for women with PCOS.


Metformin inhibits the production of sugar from the liver, decreases fat production, increases the burning of fat and inhibits new glucose molecule formation. This results in a decrease in circulating insulin and glucose.


Can Metformin cause weight loss?

A short survey conducted on Mr Karoshi’s Instagram: 61% of followers believe that Metformin can help women to lose weight


Metformin alone does not help to achieve weight loss in women with PCOS and obesity. Therefore, lifestyle improvements and supporting women with individualised assessments, setting goals and using a combination of diet and exercise remain the first-line approach.


Once this approach has shown weight loss, then adding Metformin at that time has shown to be beneficial rather than starting the medication as a sole agent to cause weight loss, which is not beneficial. In other words, a patient's motivation to lose weight has to be established before starting Metformin by diet, exercise and will power.


Does combining Metformin with Clomid or Letrozole help with fertility?

A short survey conducted on Mr Karoshi’s Instagram: 82% of followers believe that combining Metformin and Clomid or Letrozole can increase their chances of conception


As a first line therapy for the treatment of women who are anovulatory (lack of ovulation) and infertile with PCOS, Metformin alone is significantly less effective than Clomiphene Citrate alone.


If you have a BMI greater than 35 and a clomiphene citrate resistance, you may see a potential benefit from the combined use of Metformin with Clomiphene Citrate.


If I fall pregnant while taking Metformin, is it safe to continue the medication?

A short survey conducted on Mr Karoshi’s Instagram: Followers showing a mixed reaction to whether you should continue Metformin if you fall pregnant


Metformin appears to be safe in pregnancy, however, the usual advice is to discontinue post conception with the exception of those with existing diabetes.


The usual dose of Metformin is 850mg twice daily. It can potentially lead to unpleasant side-effects such as:


Can Metformin cause a vitamin B12 deficiency?

You should be aware that there is a strong association between Metformin treatment and decreased vitamin B12 levels in patients with PCOS. This is particularly prevalent in women with weight issues and hyperinsulinemia. The increase in a body chemical called homocysteine could be due to the decrease in its essential co-factors - folic acid and vitamin B12. Research has shown that the long-term use of Metformin in high doses (1500mg or higher daily for more than 6 months) can deplete levels of vitamin B12.


A deficiency of vitamin B12 can cause permanent neurological and nerve damage as well as mood changes and decreased energy.


How can I raise my vitamin B12 levels?

 The best absorbable form of vitamin B12 is methlycobalimum. Taking this form of the vitamin sublingually (under the tongue) is recommended. It is also recommended that patients who take Metformin have their vitamin B12 levels checked before the start of therapy and a year later.


If you are still unsure of Metformin, book an e-Consultation with Mr Mahantesh Karoshi by visiting his Top Doctors profile and checking his availability. 

By Mr Mahantesh Karoshi
Obstetrics & gynaecology

Mr Mahantesh Karoshi is a London-based women’s health expert and consultant gynaecologist, with a special interest in ovarian cysts, heavy menstrual bleeding, infertility, fibroids, and adenomyosis. He is currently one of the most highly-rated gynaecologists in London with a very good reputation amongst his patients and peers.

Mr Karoshi's work is recognised internationally, having volunteered in Ethiopia’s Gimbie Hospital, and later receiving the Bernhard Baron Travelling Fellowship from the Royal College of Obstetricians and Gynaecologists which led to his work in the University of Buenos Aires. Here he worked on the techniques needed to surgically manage morbidly adherent placental disorders - a serious condition that can occur in women with multiple caesarean sections.

He believes in an open doctor-patient relationship, being sure to include the patient and educating them so that they understand their condition better and they can be directly involved in their care and management at every stage. Aside from his clinical work, he is actively involved in research, which together with his experience, has given him the opportunity to publish the first stand-alone textbook on postpartum haemorrhage which was launched by HRH Princess Anne.

At the core of Mr Karoshi's practice is a high standard of professionalism where patients are involved in their treatment and where the latest techniques and advancements are used to provide an extremely high level of care.

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