Metformin side effects: what's normal and what isn't

Reviewed by the JForH team · 2026-10-30

The most common side effects of metformin are stomach upsets such as loose motions, gas and nausea. They usually settle within a few weeks and are less likely if you take it after meals and build the dose up slowly. Long-term use can lower vitamin B12, which affects up to 1 in 10 people. ICMR says the dose depends on kidney function: halve it below an eGFR of 45 and stop below 30. Don't stop metformin on your own; talk to your doctor.

What are the common side effects of metformin?

Stomach problems. Loose motions, gas, nausea, stomach pain and a poor appetite are the ones people notice most. In the UK product label for Glucophage, a common brand of metformin, these are listed as very common, meaning more than 1 in 10 people get them, mostly when starting.

Some people also notice a change in taste. Most of these effects ease after a couple of weeks as the body adjusts.

Metformin se loose motion kyu hota hai, and how do I stop it?

Metformin works partly in the gut, which is why the gut feels it first. ICMR's 2018 guideline gives three ways to reduce it:

• Take it after meals, not on an empty stomach.
• Start low and go up slowly. ICMR suggests starting at 500 mg a day after meals and adding 500 mg every two weeks, up to a maximum of 2,500 mg a day.
• Ask about a sustained-release (SR) tablet, which many people find easier on the stomach.

If loose motions are bad enough that you can't keep fluids down, call your doctor the same day. You could get dehydrated, and that matters with metformin.

Does metformin cause vitamin B12 deficiency?

It can. ICMR says long-term use may be linked to low vitamin B12. In 2022 the UK medicines regulator, the MHRA, said low B12 is a common side effect that may affect up to 1 in 10 people taking metformin.

The risk is higher with a bigger dose, many years of use, and some other factors the MHRA lists:

• a diet with few sources of B12. Strict vegetarian and vegan diets are low in B12, which matters for many Indian families.
• older age, or stomach and gut conditions that reduce absorption.
• acid-reducing tablets such as omeprazole or pantoprazole, taken long term.

Signs of low B12 include extreme tiredness, a sore red tongue, pins and needles, and pale or yellowish skin. Numb feet can look like diabetic nerve damage, so a B12 test helps tell them apart. Ask your doctor for one. If it's low, B12 can be replaced while you carry on with metformin.

Is metformin bad for the kidneys?

Metformin isn't known to damage healthy kidneys. The concern runs the other way: the kidneys clear metformin from the body, so if they are weak, it can build up. That's why your doctor checks your kidney function, shown as eGFR on your report.

ICMR gives these rules:

The US FDA reached a similar view in 2016, after studies showed metformin can be used in mild to moderate kidney disease.

What is lactic acidosis, and should I worry?

It's a build-up of acid in the blood. ICMR calls it rare, and very uncommon unless metformin is given to someone who shouldn't take it, such as a person with severe kidney, liver, heart or lung problems, a serious infection, or heavy alcohol use.

Warning signs include vomiting, stomach pain, muscle cramps, fast or difficult breathing and severe tiredness. If you have these, get emergency help.

Do I need to stop metformin before a CT scan or surgery?

Often, yes. ICMR advises stopping metformin at least 24 hours before major planned surgery or a scan that uses contrast dye. Tell the hospital you take metformin, and ask your doctor when to restart.

Does metformin cause low sugar?

Rarely on its own, says ICMR. Lows are more likely if you also take insulin or a sulfonylurea such as glimepiride or gliclazide. Under 70 mg/dL is low and needs treating straight away.

Jan Aushadhi metformin price: how much does it cost?

Very little. Sources we found put Jan Aushadhi metformin 500 mg at between about ₹6 and ₹21 for a strip of 10, against about ₹60 for some branded strips. We couldn't confirm the current price on the official Jan Aushadhi list, so ask at your nearest Kendra.

Generic and branded metformin contain the same medicine. If cost is why you skip doses, tell your doctor and ask whether a generic suits you.

How much does metformin lower HbA1c?

On its own, by about 1.1 percentage points on average, compared with a dummy pill. That comes from a 2012 pooled analysis of trials. So an HbA1c of 8.2% might fall to around 7.1%, though results vary from person to person.

Can I stop metformin because of side effects?

Not on your own. If you stop, your sugar is likely to rise again. Tell your doctor what's happening. They can change the dose, the timing or the type of tablet, or check your B12 and kidneys.

This guide is for education and does not replace advice from your own doctor.

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Last updated: 2026-10-30. Educational information, not medical advice. Talk to your doctor before changing your treatment.