Metformin: uses, dosage and side effects
Metformin is a biguanide medicine taken as a tablet and used mainly for type 2 diabetes, where it is usually the first medicine prescribed. It lowers blood sugar without causing weight gain and, on its own, rarely causes low blood sugar. In Ireland it is prescription-only. This page explains what metformin is used for, how it is taken, which side effects are reported most often, what the schemes cover and how continuing an established prescription works. It is information, not an offer of the medicine.
What metformin is used for
Metformin is used to treat type 2 diabetes in adults and children, on its own or together with other diabetes medicines including insulin. It works mainly by reducing the amount of glucose the liver releases and by making the body more sensitive to its own insulin, so it lowers blood sugar without pushing the pancreas to produce more. That is why it does not usually cause low blood sugar when taken alone and why it does not lead to weight gain. It is also prescribed by specialists in polycystic ovary syndrome and in some cases of prediabetes, which are decisions made outside or at the edge of the licensed indication. Metformin does not replace diet and physical activity; it works alongside them, and the benefit is measured through your HbA1c and other checks rather than through how you feel from day to day. Treatment is normally long term with regular review of kidney function.
Side effects of metformin
The commonest side effects are digestive: nausea, diarrhoea, abdominal pain, loss of appetite and a metallic taste. They are usually worst in the first weeks, improve with time, and are much less troublesome when the dose is built up slowly and the tablets are taken with or just after food. A modified-release form is often better tolerated by people whose gut symptoms persist. Long-term use is associated with reduced absorption of vitamin B12, which is why B12 is checked periodically, particularly in anyone with anaemia or nerve symptoms. The serious risk is lactic acidosis: very rare, but more likely with significantly reduced kidney function, dehydration, severe infection, heart or liver failure and heavy alcohol use. Stop the tablets and seek urgent medical help immediately if you develop deep or rapid breathing, severe weakness, unusual muscle pain, vomiting with abdominal pain or a feeling of cold. In an emergency in Ireland ring 112 or 999.
Dosage and how to take it
Standard metformin tablets are taken with or just after meals, usually two or three times a day, while modified-release tablets are normally taken once a day with the evening meal and are swallowed whole rather than crushed or chewed. Treatment begins at a low dose and is increased in steps over weeks, which is the single most effective way to avoid the gut side effects that make people give up on it. The maintenance dose is set by your prescriber according to blood sugar control and kidney function. If you miss a dose, take the next one at the usual time with food rather than doubling up. During an illness with vomiting, diarrhoea or fever, or if you cannot drink normally, contact your GP, because dehydration is when the very rare risk of lactic acidosis rises. Metformin is also paused around scans using iodinated contrast and around some surgery.
Is metformin available without a prescription in Ireland?
No. Metformin is a prescription-only medicine in Ireland and cannot be bought over the counter. The requirement is clinical rather than bureaucratic: the dose depends on kidney function, which changes over time and has to be checked, and the medicine has to be paused in situations such as dehydration, serious illness, certain scans and some operations. Diabetes treatment also comes with monitoring, eye and foot checks and cardiovascular risk management that a prescription-based system keeps attached to the medicine. Buying metformin from a website that asks no medical questions removes all of that and gives no assurance about what the tablets contain. A prescription written by a doctor in another EU or EEA country can be dispensed in Ireland when it carries the details required for cross-border prescriptions, and the Pharmaceutical Society of Ireland publishes guidance for pharmacists on how to handle such prescriptions.
Continuing treatment and repeat prescriptions
If you are already taking metformin, your dose is unchanged and your kidney function has been checked recently, you can ask for a repeat prescription through our online medical questionnaire. There is no video consultation, no telephone appointment and no live chat: you answer a structured set of medical questions and a doctor reviews your answers separately. The review is carried out by lek. Damian Wojno, a doctor registered in Poland, PWZ no. 3211301, working to Polish professional rules. If he agrees that treatment can continue, you receive a cross-border prescription as a PDF by e-mail, prepared with the fields set out in the Annex to Directive 2012/52/EU. You print it, bring it to any pharmacy in Ireland and identify yourself with your ID document; there is no PIN code and nothing to look up in an Irish system. This route bridges an existing prescription and does not replace the diabetes reviews, blood tests and eye screening that go with the condition. The fee of 19,90 € covers the medical assessment and not the issuing of a document: if the doctor declines on medical grounds the fee is returned, but it is not returned if you do not send the documentation the doctor asks you for.
Cost and reimbursement in Ireland
Metformin is an old, widely manufactured medicine, so private prices are among the lowest of any long-term treatment, although each pharmacy sets its own. More importantly, diabetes is one of the conditions covered by the Long Term Illness Scheme, under which medicines and some supplies for the condition are provided without charge to people who qualify, regardless of income. Holders of a medical card receive prescribed medicines under the GMS scheme for a small charge per item with a monthly household cap. Anyone else can use the Drugs Payment Scheme, which caps what one household pays for prescribed medicines in a calendar month; the HSE publishes the current charge and cap, so take the figure from there rather than from an older page. If you have type 2 diabetes and are paying for metformin in full, ask your GP or pharmacist whether the Long Term Illness Scheme applies to you.
Interactions and alcohol
Alcohol matters more with metformin than with most diabetes tablets, because heavy drinking and binge drinking increase the risk of lactic acidosis and can also cause low blood sugar, particularly with little food. Moderate drinking with a meal is usually acceptable, but this is worth discussing with your prescriber if you drink regularly. Medicines that reduce kidney function or cause fluid loss raise the risk too: diuretics, some blood pressure medicines and anti-inflammatory painkillers such as ibuprofen or naproxen, especially during an illness with vomiting or diarrhoea. Iodinated contrast used in some scans is a recognised reason to pause metformin, so tell the radiology department that you take it. Steroids and some other medicines raise blood sugar and can require a dose review. When metformin is combined with insulin or a sulfonylurea, the risk of low blood sugar comes from the partner medicine. Tell your pharmacist about everything you take.
Who should not take metformin
Metformin must not be used by anyone allergic to it, by anyone with severely reduced kidney function, or during an acute condition that can damage the kidneys such as dehydration, severe infection or shock. It is also contraindicated in acute or chronic conditions causing tissue oxygen shortage, including decompensated heart failure, recent heart attack and respiratory failure, and in diabetic ketoacidosis or diabetic pre-coma. Severe liver disease, acute alcohol intoxication and alcohol dependence are further contraindications. Reduced but not severely reduced kidney function usually means a lower dose plus closer monitoring rather than stopping. Tell your prescriber if you are having surgery, a scan with contrast, or if you become unwell with vomiting, diarrhoea or fever, because the tablets are usually paused. If you have anaemia or numbness in the hands or feet, mention it, since vitamin B12 deficiency is a recognised long-term effect worth checking.
Generic and brand names
The active substance is metformin hydrochloride. It is supplied by many manufacturers in Ireland as standard tablets and as modified-release tablets, and original brand names such as Glucophage remain familiar although generic versions are what most people receive. Fixed-dose combination products also exist, pairing metformin with another diabetes medicine in one tablet; those are separate products with their own leaflets and their own prescribing decisions. The one distinction to keep clear is between standard and modified-release tablets, because the dosing schedule differs and the two are not swapped tablet for tablet at the counter. On a cross-border prescription, the medicine should be named by its international non-proprietary name, metformin, together with the strength, the form and whether it is modified-release, which is what an Irish pharmacist needs to dispense the right pack.
Pregnancy and breastfeeding
Metformin is one of the diabetes medicines most used in pregnancy, and it is prescribed in pregnancy in some circumstances, including gestational diabetes, but that decision belongs with the maternity and diabetes teams rather than with an online questionnaire. Blood sugar targets in pregnancy are tighter and treatment often changes, sometimes to insulin, so anyone planning a pregnancy should have their treatment reviewed in advance. Metformin passes into breast milk in small amounts and is generally regarded as compatible with breastfeeding under medical supervision, with the infant observed. If you become pregnant while taking it, contact your GP or diabetes team promptly rather than stopping treatment on your own, because uncontrolled blood sugar in early pregnancy carries its own risks. Our online questionnaire does not lead to prescriptions for use during pregnancy or breastfeeding.
Patient information leaflet
Every pack sold in Ireland contains a patient information leaflet, and the same leaflet is published online. The Health Products Regulatory Authority (HPRA) is the medicines regulator here and lists authorised products together with their leaflets and summaries of product characteristics; medicines.ie publishes the same documents for products marketed in Ireland. Because metformin comes from many manufacturers and in two release forms, check that the leaflet matches the pack in your hand, especially the instruction about taking tablets with food and about swallowing modified-release tablets whole. Read it before starting a new pack, since the wording on warnings is updated from time to time. If anything does not match what you were told, ask your pharmacist rather than guessing; pharmacists in Ireland are registered with the Pharmaceutical Society of Ireland. A suspected side effect can be reported by you directly to the HPRA.
Who wrote and checked this page
This page was prepared by the medical content team at MEDINOW Sp. z o.o. and reviewed by lek. Damian Wojno, a doctor registered in Poland, PWZ no. 3211301. He holds no Irish registration and does not practise in Ireland; he works to Polish professional rules and issues cross-border prescriptions under Directive 2011/24/EU and Directive 2012/52/EU, which is the framework an Irish pharmacist applies when a prescription comes from another EU or EEA country. The content was verified on 29 August 2026 against the sources listed below, all of them official or regulator-published. This page is general information about a medicine: it is not personal medical advice, not a diagnosis and not an offer of the medicine itself, which we never supply. If your symptoms are new, severe or changing, contact your GP or a pharmacist; in an emergency in Ireland ring 112 or 999.
Is metformin prescription-only in Ireland?
Yes. It cannot be bought over the counter, because the dose depends on kidney function and the tablets have to be paused in situations such as dehydration or a scan with contrast. A prescription from a doctor in another EU or EEA country can be dispensed here when it carries the required cross-border details.
How long does it take to work?
Blood sugar starts to fall within days, but the effect is judged over about three months through HbA1c, which reflects average glucose over that period. The dose is also built up slowly, so the first weeks are not a fair test of the medicine.
What are the common side effects?
Nausea, diarrhoea, abdominal discomfort, loss of appetite and a metallic taste, mostly early and much reduced by taking tablets with food and increasing the dose slowly. Long-term use can lower vitamin B12, which is checked periodically.
Can I drink alcohol with it?
Moderate drinking with food is usually acceptable, but heavy or binge drinking should be avoided, because it raises the risk of lactic acidosis and can cause low blood sugar. Tell your prescriber honestly how much you drink, because it changes the safety picture.
How do I get a repeat prescription?
If your dose is unchanged and kidney function has been checked recently, you can complete our online questionnaire and a doctor reviews it separately; there is no video consultation. If treatment can continue you receive a cross-border prescription as a PDF by e-mail. The fee covers the assessment, not the issuing of a document.