Metformin: Uses, side effects and cautions

August 16, 2023
6 minute read

Join us as we explore our complete guide to the antidiabetic medication, metformin. We'll cover how metformin works, how to take it, potential side effects, taking metformin while pregnant, and much more.

Type 2 Diabetes (T2D) is one of the most prevalent chronic conditions around the world. It is a serious, lifelong condition that results in levels of blood glucose being too high (hyperglycaemia).

Across the UK, roughly 4.9 million people have diabetes, and a further 850,000 are thought to be living with undiagnosed diabetes. A further 13.6 million people are at increased risk of diabetes.

What is metformin and what is metformin used for?

Originally synthesised in the 1940’s during a search for antimalarial drugs, metformin is a drug with over 60 years of history of use in the treatment of Type 2 Diabetes (T2D).  

Metformin is widely used to treat early stage T2D and even prevent this condition in those that have a high risk of developing it.

Metformin is regarded as a safe, well-tolerated and effective first-line medication for diabetes due to its ability to reduce blood glucose levels, increase your body’s sensitivity to insulin (the hormone responsible for the regulation of blood sugar levels) and reduce intestinal absorption of glucose.

Early in the diagnosis of T2D, lifestyle interventions such as diet optimisation and increased levels of exercises are recommended to keep your blood sugar levels in check. Metformin is often prescribed when these strategies are no longer effective at lowering hyperglycaemia.

Metformin is also used in Polycystic Ovarian Syndrome (PCOS) to decrease insulin levels, which results in a normalised menstruation cycle. It’s important to know that metformin increases the pregnancy potential in premenopausal women.

Metformin represent the first choice of medicine in the treatment of type 2 diabetes

How does metformin work?

Metformin reduces the amount of glucose that your liver produces, increasing insulin sensitivity in the body and reducing intestinal absorption of glucose.

Metformin is one of the only weight-neutral antidiabetic medications, meaning that unlike other medications used to treat T2D, metformin won’t make you gain weight.

In fact, metformin can be expected to lead to minor weight loss, as it reduces your appetite.

How to take metformin

Your doctor will prescribe you a dose of metformin that can be up to 2000 mg/day. Metformin can be taken as standard-release tablets and slow-release tablets.

Standard-release tablets lead to a quick release of metformin in the body, and you might find that you have to take them several times per day, depending on the specific dose that you’ve been prescribed.

Slow-release tablets lead to a slower, sustained release of metformin in the body. If you’re prescribed slow-release tablets, you’ll likely have to take just one dose per day.

It is recommended that you take metformin with a meal as this will help reduce any possible side effects.

Metformin is used to lower insulin and blood sugar levels in PCOS
Metformin side effects

Metformin can produce side effects, like most other medications, however the side effects are generally mild, and don’t affect everyone.

Some of the most common side effects of metformin include:

  • Nausea
  • Vomiting or diarrhoea
  • Stomach ache
  • Loss of appetite
  • A metallic taste in the mouth

These side effects generally occur in up to 30% of patients that take metformin.

Metformin can also lead to low blood sugar levels (hypoglycaemia). It’s unlikely that metformin alone will cause low blood sugar, as this happens most often when metformin is taken in combination with other diabetes medicines.

How long does it take for metformin to work?

Once you start taking it, metformin will begin to lower your blood sugar levels within 48 hours, with its effects peaking at day 4-5. This also depends on dosage and the time when you take it.

If you have been diagnosed with pre-diabetes you might not experience symptoms of diabetes, in which case you should not expect to feel any different when taking metformin. It’s important to keep taking it as prescribed, as “not feeling” a medication working does not mean it isn’t working.

Metformin in pregnancy

Gestational diabetes is dangerous as high levels of blood sugar have been associated with congenital malformations, miscarriage and stillbirth.

Metformin is effective at reducing blood glucose levels in gestational diabetes and is the preferred medication for this purpose.

While metformin does cross the placenta and enters the milk when breastfeeding in low amounts, it won’t harm your baby.

Metformin cautions

Always ensure that you let your doctor know which medications you are taking. Metformin can interact with some medicines such as steroids, diuretics, other diabetes medicines, heart medication and male/female hormones.

If you are taking any of these medications along with metformin, it is likely that your blood sugar levels will have to be checked more regularly than usual.

To learn more about metformin, please this this official NHS article.

Do you have more questions about metformin? Get in touch with our pharmacy team to speak to a knowledgeable pharmacist that will be able to answer any further questions.

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