Starting Metformin: What You Really Need to Know

For many people, being prescribed metformin is a quiet but important moment. It often comes early — sometimes at diagnosis — and it can raise questions that are not always spoken out loud.

Some people worry it means their diabetes is “getting worse”. Others wonder whether they have already failed at managing things through food or lifestyle alone. And many feel uncertain because they have heard stories about side effects, particularly stomach upset.

It’s important to say this clearly: starting metformin is not a sign of failure. In modern diabetes care, it is often a protective step — one that helps stabilise blood sugar levels, reduce long-term risk, and support the body while other changes are taking effect.

Metformin is one of the most studied medications in diabetes medicine. When it is started thoughtfully and adjusted carefully, most people tolerate it well and benefit from it. Understanding why it is prescribed and how it is started makes that process much easier.

metformin medication for type 2 diabetes-Brand names include: Glucophage; Glucophage XR; Diaformin; Diabex; Fortamet; Glumetza; Riomet

Why metformin is often started early

In type 2 diabetes, one of the main underlying problems is insulin resistance. This means the body’s own insulin is present, but it does not work as effectively as it should.

Metformin helps by improving insulin sensitivity and by reducing the amount of glucose (sugar) released by the liver, particularly overnight and between meals. This is why fasting blood sugar levels often improve first.

Starting metformin early helps support the body before blood sugar levels drift higher and become harder to control. It does not replace the importance of food choices, physical activity, or weight management — rather, it works alongside them.

This approach is supported by international guidelines, including NICE and the joint ADA/EASD consensus, which recommend metformin as first-line treatment for most people with type 2 diabetes.

If you’re starting metformin — or you’ve been taking it and still feel unsure about it — Dr Sultan has created this clear, practical guide to help you understand what it’s doing and what to expect.

Do you want to know more about Metformin?

Check out our articles for more content on metformin.

Is Metformin safe in Pregnancy?

metformin is a medication for people with diabetes

Metformin. A wonder drug?

woman holding stomach - some people who use metformin experience diarrhoea

Metformin and Diarrhoea

Vitamin B12 vials and tablets to treat vitamin B12 deficiency caused by metformin

B12 deficiency and Metformin

How metformin is usually started

One of the most important things to understand about metformin is that starting slowly matters. Many side effects are related not to the medication itself, but to how quickly it is introduced.

Metformin is typically started at a low dose and increased gradually over several weeks. This allows the digestive system time to adapt. Taking metformin with meals also reduces stomach upset.

Some people are prescribed an extended-release (modified-release) form, which releases the medication more slowly and is often easier to tolerate.

If you would like a practical, step-by-step overview of how metformin is usually started, including dose increases, timing with meals, and what to do if side effects occur, we’ve created a short, specialist-written guide you can download.

Free metformin starter guide:
A clear, practical explanation of how doctors usually introduce metformin safely in real life

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It’s normal for blood sugar improvements to happen gradually. Metformin is not a “quick fix” — it is designed to provide steady, long-term benefit.

Side effects, diarrhoea, and vitamin B12

The most common side effects of metformin affect the gut. These include nausea, bloating, and diarrhoea, particularly in the first few weeks.

While these symptoms can be frustrating, they are usually temporary. Slower dose increases, taking metformin with food, or switching to an extended-release form often leads to significant improvement.

A clear explanation of why this happens — and what helps — is available here: Metformin and diarrhoea: why it happens.

With long-term use, metformin can reduce absorption of vitamin B12 in some people. This does not mean it is unsafe, but it does mean monitoring matters, particularly if symptoms such as fatigue, tingling, or numbness appear.

You can read more about this here: Vitamin B12 deficiency and metformin.

Alcohol and Metformin

You need to be cautious and drink sensibly as metformin can interfere with the way the body works in the liver (Alcohol use of diabetes patients: The need for assessment and intervention). Remember that alcohol can also lower your blood sugars and put you at risk of hypoglycaemia.

Pregnancy and Metformin

The goals in pregnancy for someone with diabetes are that blood sugars should try to be maintained at normal levels throughout the pregnancy so that the risk of complications at birth are no different to that of a pregnant mother-to-be without diabetes. Globally about 18% of pregnant women develop gestational diabetes as a result of not being able to produce enough insulin needed in pregnancy, the risk accumulating as the pregnancy develops and baby gets larger. In some countries and among certain ethnic groups the risk of gestational diabetes is greater along with factors such as your mother having diabetes; being overweight or previous gestational diabetes in pregnancy.

Controlling blood sugars minimizes risk of baby being large for gestational age at birth and as a consequence reducing the likelihood of developing pre-eclampsia; needing induction or requiring a cesarean-section. It also decreases the chances of baby not experiencing complications related to sudden changes in blood glucose levels once the umbilical cord is cut and it no longer has the blood supply of its mother (known as hypoglycaemia). These are all really important reasons to get it right in pregnancy and many doctors are now prescribing metformin with very positive outcomes at birth.

Metformin can be used alone or with the addition of insulin if sugar levels are still too high. Not having to inject, less risk of low blood sugars and few side effects, the benefits of use are easy to see. Side effects if experienced are most commonly nausea and diarrhoea which should settle soon after commencing.

For more information on metformin use in women with gestational diabetes, read our article Metformin in Pregnancy: is it safe?

When not to take Metformin

Metformin is not suitable for some people. There are some conditions that can prevent you from taking metformin.

Lactic Acidosis

The use of metformin is associated with lactic acidosis (Metformin associated lactic acidosis). This is extremely rare but very serious and accounts for less than 1% of all patients taking metformin. Since the removal of one type of metformin, phenformin, from the market a review of all patients over a 2-year period (11,800 patients) revealed only 2 cases. It often presents as vague symptoms due to a large build-up of toxic lactic acid in the body. Symptoms include nausea, vomiting, abdominal pain, breathing difficulties and low blood pressure: if suspected immediate medical assistance is needed.

If you have any of the following medical problems then Metformin may not be suitable. The list is based on those at high risk of lactic acidosis:

Chronic kidney problems
Liver disease
Current alcohol abuse
Acute or unstable Heart failure including heart attacks
Severe, serious infections that require hospital admission (causing poor circulation)

Surgery or scans

If you're having surgery or scans that involve administration of a contrast dye may require you to stop taking some medications. You may need to stop metformin on admission and not restart until at least 48 hours afterwards dependent on the advice of your doctors. The reason? To prevent any possibility of lactic-acid build up and ensure the kidneys and heart are functioning well.

How metformin fits into the bigger picture

Metformin is often continued even if insulin is added later. Insulin lowers blood sugar directly, while metformin improves insulin sensitivity and reduces glucose output from the liver. Used together, they can lead to more stable control with lower insulin requirements.

If insulin is part of your treatment, you may find this helpful: Basal insulin explained.

In people with prediabetes, metformin is not required for everyone. However, strong evidence from the Diabetes Prevention Program shows it can significantly reduce progression to type 2 diabetes in higher-risk individuals, particularly when combined with lifestyle changes.

Most importantly, metformin works best when it is part of a broader understanding of how food, activity, weight, medications, and monitoring fit together.

What are the pros and cons of taking metformin?

With all of the information above, you might be wondering what the pros and cons of metformin are. As discussed, there are a number of benefits of metformin. There are also some side effects, for example diarrhoea. Below is a quick and simple list of the metformin pros and cons.

Pros of metformin

Lowers the amount of glucose made by the liver - which can result in the body’s cells being more sensitive to the action of insulin!
Relatively inexpensive
Usually well tolerated by most people
Taken as a tablet
Affordable
Cancer prevention
Cardiovascular benefits
Anti-ageing
Links to dimentia prevention
May assist with weight loss
Can be used during pregnancy

Cons of metformin

Diarrhoea
Nausea
Vitamin B12 deficiency
Metallic taste
Odour

It's important that before starting any medication, that you and your doctor discuss all the pros and cons.

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Spend 30–40 minutes with a diabetes specialist learning how treatment decisions are made and what actually helps stabilise blood sugar levels in real life. Watch the free diabetes masterclass.

Frequently Asked Questions

What is metformin?

Metformin is a first-line oral medication for type 2 diabetes. It helps lower blood glucose levels by reducing the amount of glucose produced by the liver and improving the body’s response to insulin.

How does metformin work?

Metformin decreases hepatic (liver) glucose production, improves insulin sensitivity, and reduces glucose release into the bloodstream. In some people it can also modestly improve cholesterol and triglyceride levels.

What are the benefits of metformin?

Metformin helps improve glucose control, is generally weight-neutral, may support small weight reductions in some people, and is low cost and well studied. For many adults, it forms the foundation of long-term diabetes treatment.

How should I take metformin?

Metformin is typically started at a low dose, such as 500 mg once daily with food, and increased gradually over one to two weeks to reduce stomach upset. Usual doses range up to 2,000–3,000 mg per day depending on the formulation and your clinician’s advice.

What are the side effects of metformin?

Common side effects include diarrhoea, nausea, abdominal discomfort, and a metallic taste—especially when treatment begins. Long-term use may reduce vitamin B12 levels. Speak with your clinician if symptoms persist or worsen.

Can I drink alcohol while taking metformin?

Alcohol should be consumed in moderation. Excessive drinking increases the risk of side effects including lactic acidosis. Alcohol can also lower blood glucose and increase hypoglycaemia risk when used with certain medications.

Can metformin be taken during pregnancy?

Metformin is used in some pregnancies, including gestational diabetes, depending on local guidelines and clinician advice. Diabetes management in pregnancy should always be individualised and closely supervised.

When should I avoid taking metformin?

Metformin may not be suitable for people with severe kidney impairment, significant liver disease, dehydration, or medical conditions that reduce oxygen delivery to tissues. It may also need to be paused around surgery or contrast imaging. Follow your clinician’s instructions.

Why does metformin cause diarrhoea?

Gastrointestinal upset is common when starting or increasing the dose. Taking metformin with meals, using gradual dose titration, or switching to an extended-release version often improves tolerance. Symptoms usually settle within days to weeks.

Why should I take metformin?

Metformin is an effective, well-researched starting therapy for type 2 diabetes. It improves glucose control, may delay the need for additional medication, and has a long safety record. Your clinician will confirm whether it is suitable for you.