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Metformin: what to be careful with
Metformin lowers blood glucose mainly by reducing the amount of glucose the liver releases, and is usually the first medicine used in type 2 diabetes.
General information only, and not exhaustive. This is not medical advice, not a full list of interactions, and not a reason to start, stop or change a medicine. Interactions depend on the exact drug, the dose, your other medicines and your own health — a pharmacist or doctor is the one who decides. Always read the leaflet that came with your medicine, and ask your pharmacist before adding anything, including supplements.
Group, not a brandATC A10BA02
Examples in this group: metformin, metformin modified release. Interactions usually belong to the whole group, but your own leaflet is brand-specific — always the final word.
Food and drink to be careful with
- Take it with or straight after food. The commonest problem with metformin is nausea, bloating and diarrhoea in the first weeks. Taking it with a meal is the standard advice in the leaflet and makes a real difference for most people.
- Vitamin B12. Long-term metformin reduces B12 absorption in a proportion of people. That is why B12 is sometimes checked on a routine blood test after several years of treatment. It is a monitoring point, not a reason to change anything on your own.
- Carbohydrate and meal patterns. Metformin does not cause low blood sugar on its own the way insulin or sulfonylureas do, so skipping a meal is less immediately risky — but if you also take another glucose-lowering medicine, that changes.
- Dehydration and illness. Vomiting, diarrhoea or any illness with dehydration is the situation in which metformin is temporarily paused. Prescribers issue individual "sick day" instructions for exactly this; those instructions, not a web page, are the ones to follow.
Timing around meals
Standard metformin is usually taken with meals, and modified-release forms usually with the evening meal. The number of doses a day and their timing are set by the prescriber.
Alcohol
Heavy or binge drinking is the concern, because it and metformin both push in the same direction on lactic acid, and because alcohol affects blood glucose unpredictably. Leaflets advise avoiding excessive intake rather than total abstinence.
Other things to watch
- Any scan using iodinated contrast dye means metformin is usually paused around the procedure — the imaging department will say so.
- Kidney function decides whether metformin can be used and at what dose; it is checked regularly for that reason.
- Persistent GI upset is often solved by switching to the modified-release form, which is a prescriber's decision.
If anything here does not match what you were told, or you notice a new symptom after starting a medicine, contact your pharmacist or doctor — do not just stop taking it. Stopping some medicines suddenly is more dangerous than any food interaction.
Source: The product's own Summary of Product Characteristics and patient information leaflet, published per medicine by the licensing authority. The B12 and contrast-media points are standing entries in the metformin product information. · checked 2026-09-02
Frequently asked questions
What should I avoid with metformin?
Take it with or straight after food is the one people ask about most: The commonest problem with metformin is nausea, bloating and diarrhoea in the first weeks. Taking it with a meal is the standard advice in the leaflet and makes a real difference for most people. This is general information — your leaflet and pharmacist have the specifics.
Can I drink alcohol with metformin?
Heavy or binge drinking is the concern, because it and metformin both push in the same direction on lactic acid, and because alcohol affects blood glucose unpredictably. Leaflets advise avoiding excessive intake rather than total abstinence.
Should metformin be taken with food?
Standard metformin is usually taken with meals, and modified-release forms usually with the evening meal. The number of doses a day and their timing are set by the prescriber.
Other medicine groups
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Levothyroxine
Levothyroxine replaces the thyroid hormone the body is not making enough of, in an underactive thyroid.
Warfarin
Warfarin thins the blood by blocking the vitamin K-dependent clotting factors, and is used to prevent and treat blood clots.
DOACs (direct oral anticoagulants)
DOACs thin the blood by directly blocking a single clotting factor, and are used to prevent stroke in atrial fibrillation and to treat and prevent venous clots.
SSRIs and SNRIs
These antidepressants raise the availability of serotonin (and for SNRIs also noradrenaline) in the brain, and are used for depression and several anxiety conditions.
NSAIDs
NSAIDs reduce pain, fever and inflammation by blocking prostaglandin production.
All medicine groups · Alcohol units and clearance · Blood test reference ranges
Track meals and symptoms alongside your medicines
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