Mounjaro: uses, dosage and side effects
Mounjaro contains tirzepatide, a dual GIP and GLP-1 receptor agonist given as a once-weekly injection under the skin. It is authorised in the European Union for type 2 diabetes and for weight management alongside a reduced-calorie diet and more physical activity. In Ireland it is prescription-only, so a doctor has to assess you before it can be prescribed. This page explains what the medicine does, how it is taken, which side effects are reported most often and how continuing treatment works. It is information, not an offer of the medicine.
What Mounjaro is used for
Mounjaro is used to improve blood sugar control in adults with type 2 diabetes, and for weight management in adults living with obesity or with overweight plus a weight-related health problem, always alongside diet and physical activity. Tirzepatide acts on two gut hormone receptors, GIP and GLP-1. Through them it increases insulin release when blood sugar is high, reduces glucagon, slows how quickly the stomach empties and lowers appetite, so most people eat less without consciously restricting themselves. It is not insulin and it is not a treatment for type 1 diabetes. Neither is it a short-term slimming aid: the licence describes long-term use with regular review, and weight tends to return when treatment stops if eating and activity habits have not changed. Your prescriber decides which of the two licensed uses applies to you, because that decision also affects monitoring, reimbursement and which other medicines you take with it.
Side effects of Mounjaro
The side effects reported most often with tirzepatide affect the gut: nausea, diarrhoea, vomiting, constipation, indigestion, burping and reduced appetite. They are usually strongest in the first weeks and after each dose increase, and they often settle as the body adjusts. Reactions at the injection site, tiredness, dizziness and hair thinning are also described in the product information. Low blood sugar is uncommon with tirzepatide on its own but becomes far more likely when it is combined with insulin or with a sulfonylurea, which is why those doses are usually reviewed. Less common but serious problems include inflammation of the pancreas, gallstones and gallbladder inflammation, and severe allergic reactions. Stop the injection and seek urgent medical help immediately if you develop severe, persistent abdominal pain that spreads to your back, if you cannot keep fluids down, or if your face or throat swells and breathing becomes difficult. In an emergency in Ireland ring 112 or 999.
Dosage and how to take it
Mounjaro is injected under the skin of the abdomen, thigh or upper arm once a week, on the same day each week, with or without food. Treatment starts at a low dose and is increased in steps, and each step is a prescribing decision made by the doctor monitoring you, not something to adjust yourself. Rotate the injection site to protect the skin. If you miss a dose, the leaflet explains when it can still be taken and when to skip it and go back to your usual weekly day; ask your pharmacist rather than doubling up. Pens are kept in the fridge until first use, and the leaflet gives the storage limits once a pen is in use. Because tirzepatide slows stomach emptying, drinking enough fluid and eating smaller meals makes the first weeks easier. Never share a pen or a needle, even after cleaning, because that can transmit infection.
Is Mounjaro available without a prescription in Ireland?
No. Mounjaro is a prescription-only medicine in Ireland and no pharmacy may supply it over the counter. It was authorised centrally through the European Medicines Agency, so the same product information applies across the European Union, and the HPRA supervises its use here. Anything offered online without a prescription, or shipped by an unregistered seller, sits outside the legal supply chain; injectable products bought that way have repeatedly turned out to be falsified. Supply of tirzepatide has also been constrained at times across Europe, which is exactly the situation in which unregulated sellers appear. 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. We do not sell the medicine and we do not send medicines to Ireland.
Continuing treatment and repeat prescriptions
If a prescriber has already started you on Mounjaro and you want to continue the same treatment, you can ask for a prescription through our weight management questionnaire. There is no video consultation, no telephone appointment and no live chat: you complete a structured medical questionnaire and a doctor assesses it separately. The assessment is carried out by lek. Damian Wojno, a doctor registered in Poland, PWZ no. 3211301. If he agrees that treatment can continue, you receive a cross-border prescription as a PDF by e-mail, with the fields set out in the Annex to Directive 2012/52/EU, and you bring the printout to any pharmacy in Ireland with your ID document. There is no PIN code and nothing to look up in an Irish system. We never supply the medicine itself, and we do not state how long an assessment takes. The fee covers the medical consultation, not the issuing of a document - the doctor decides after reviewing your form. If the doctor declines for medical or legal reasons, we refund the fee in full. If the doctor asks you for documentation, you have at least 7 days to provide it, and we will remind you before the deadline; if the consultation cannot be completed, we also refund the full amount.
Cost and reimbursement in Ireland
What you pay depends on the scheme you are in. If you hold a medical card, prescribed medicines are supplied under the GMS scheme for a small charge per item, subject to a monthly household cap. Without a medical card, the Drugs Payment Scheme caps what one household pays for prescribed medicines in a calendar month; the HSE publishes the current charge and cap, so check the figure there rather than relying on an older page. The Long Term Illness Scheme covers medicines for a defined list of conditions, and diabetes is on that list, which matters for people prescribed tirzepatide for type 2 diabetes. Use for weight management is treated separately from use for diabetes, and reimbursement is decided separately too, so many people pay privately for that indication. Pharmacies set their own private prices, so the same pack can cost different amounts in different pharmacies.
Interactions and alcohol
Tirzepatide slows how quickly the stomach empties, so it can change how fast other medicines taken by mouth are absorbed. One point about the contraceptive pill is worth correcting, because it circulates widely: in the study with a combined pill, a single dose of tirzepatide did measurably reduce the amount of hormone absorbed, but the European product information judges that reduction clinically irrelevant and asks for no change to contraception. The ordinary rule still stands: if you vomit or have severe diarrhoea soon after taking the pill, follow the leaflet for your own contraceptive. The interaction that matters most in practice is with other diabetes medicines: combined with insulin or a sulfonylurea, tirzepatide clearly raises the risk of low blood sugar, so those doses are usually reviewed when it is started. Tell your prescriber and your pharmacist about everything you take, including medicines bought over the counter and herbal products. Alcohol is not formally forbidden, but it moves blood glucose in both directions, adds calories and makes nausea and vomiting worse, so heavy or binge drinking is a poor match for this treatment. If you drink, keep it modest and never on an empty stomach.
Who should not take Mounjaro
Tirzepatide must not be used by anyone who has had a hypersensitivity reaction to it or to any ingredient of the pen. It is not a treatment for type 1 diabetes and is not used for diabetic ketoacidosis. Caution and closer supervision apply if you have had pancreatitis, gallstones, severe gut problems such as gastroparesis, diabetic retinopathy under treatment, or significantly reduced kidney function, particularly if vomiting or diarrhoea leaves you dehydrated. Anyone taking insulin or a sulfonylurea needs those doses reviewed. People who diet very hard while on treatment can lose muscle as well as fat, so protein intake and activity matter. Before any procedure under general anaesthesia or deep sedation, and before an endoscopy, tell the team that you use a GLP-1 medicine. Slower stomach emptying can leave food in the stomach despite the fasting you were told to follow, and that food can enter the lungs as anaesthesia is started. If you are unsure whether something in your history counts, mention it rather than leaving it out.
Generic and brand names
The active substance is tirzepatide and the brand marketed in Europe for both licensed uses is Mounjaro, supplied as a pre-filled pen. There is no generic tirzepatide: the molecule is still under patent, so any product presented as a cheap generic version is not a licensed medicine. Tirzepatide is often discussed alongside semaglutide, sold as Ozempic for type 2 diabetes and as Wegovy for weight management, but these are different molecules with different dosing and they are not interchangeable. Compounded or custom-mixed tirzepatide sold in vials online is not authorised in the European Union and its contents cannot be verified. When a prescription is written for use in Ireland, the medicine should be named by its international non-proprietary name as well as by its brand, which is what a pharmacist here expects to see on a prescription written in another EU country.
Pregnancy and breastfeeding
Tirzepatide is not recommended during pregnancy. Human data are limited, and losing weight during pregnancy is not appropriate, so the product information advises stopping the medicine if a pregnancy is planned or discovered; because of the long half-life the European product information sets that interval at at least one month before a planned pregnancy. Effective contraception is advised during treatment, and no special change to an oral contraceptive is required for tirzepatide. It is not known whether tirzepatide passes into human breast milk, so it is not recommended while breastfeeding. If you become pregnant unexpectedly while using it, contact your prescriber or GP rather than stopping other diabetes treatment on your own, because blood sugar control still has to be managed. 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. For Mounjaro the European Medicines Agency also publishes the full product information, because the medicine was authorised centrally for the whole European Union. Read the leaflet before you start a new pack, because wording on storage, warnings and side effects is updated from time to time and the version in your pack may be older than the version online. If anything there 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 Mounjaro prescription-only in Ireland?
Yes. Tirzepatide is prescription-only here and no pharmacy can supply it without a prescription. A prescription issued 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 PSI guidance tells pharmacists how to handle those.
How long does it take to work?
Effects on blood sugar begin over the first weeks, while changes in weight build up gradually across months of continued treatment together with diet and activity. Because the dose is increased in steps, the full effect of your prescribed dose is not visible in the first week.
What are the common side effects?
Mostly gut effects: nausea, diarrhoea, vomiting, constipation, indigestion and reduced appetite, strongest early and after a dose increase. Injection site reactions and tiredness are also reported. Severe abdominal pain spreading to the back needs urgent medical assessment.
Can I drink alcohol with it?
There is no formal ban, but alcohol destabilises blood glucose, adds calories and worsens nausea and vomiting. If you drink, keep the amount modest and avoid drinking on an empty stomach, particularly if you also take insulin or a sulfonylurea.
How do I get a repeat prescription?
If a prescriber already started you on tirzepatide, you can complete our weight management 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 and bring the printout to any pharmacy with your ID document. The fee covers the assessment, not the issuing of a document.