Weight loss injections: Mounjaro, Wegovy and Ozempic

What is actually in each injection

Two of these four products contain the same active substance. Ozempic and Wegovy are both semaglutide, Saxenda is liraglutide, and Mounjaro is tirzepatide. Semaglutide and liraglutide are GLP-1 receptor agonists, which imitate a gut hormone released after eating; tirzepatide acts on the GIP receptor as well as the GLP-1 receptor. All of them are prescription-only medicines in Ireland and all are given by subcutaneous injection with a pen.

The practical differences matter more than the pharmacology for most people. Saxenda is injected daily; semaglutide and tirzepatide are injected once a week. All of them start at a low dose that is stepped up over weeks, because going straight to a maintenance dose causes far more nausea. Doses are not interchangeable between products, and switching between them is a prescribing decision rather than a swap you make at home. Brand names also differ by licence rather than by strength, which is where most of the confusion on this topic starts.

Which of them is licensed for weight management

Wegovy, Saxenda and Mounjaro hold weight management licences in the EU; Ozempic does not. Ozempic is authorised for type 2 diabetes, so prescribing it for weight loss alone is off-label use, and it is one reason supply of the diabetes product has been under pressure. Mounjaro is authorised both for type 2 diabetes and for weight management. Wegovy and Saxenda are authorised for weight management only.

The licensed population is narrower than the public conversation suggests. Broadly, these treatments are licensed for adults with a body mass index of 30 or more, or 27 or more where there is at least one weight-related health problem such as high blood pressure, prediabetes, type 2 diabetes, obstructive sleep apnoea or dyslipidaemia, and always alongside a reduced-calorie diet and increased physical activity rather than instead of them. The authoritative statement of the licence for each product is its Summary of Product Characteristics, published by the European Medicines Agency and available through the HPRA.

Which injection works best

There is no single answer, and the honest version is that the trial averages and the individual result are two different things. In the studies submitted to the European Medicines Agency, average weight loss was greater with tirzepatide than with semaglutide, and greater with semaglutide than with liraglutide, but those are averages across thousands of people, with wide spread on either side. A person who cannot tolerate the drug that performs best on average will do better on the one they can actually keep taking.

Four practical factors usually decide the choice: what you tolerate, whether a daily or weekly injection suits your routine, whether you have type 2 diabetes or another condition that points to one product, and what is available and affordable at the time. Supply has been intermittent across Europe for several of these products. This page compares the medicines as information; it is not a recommendation to use any of them, and the decision belongs to a prescriber who has your history in front of them.

Side effects and who should not use these medicines

The common side effects are gastrointestinal and they are common enough to expect rather than to be surprised by: nausea, vomiting, diarrhoea, constipation, reflux, burping and abdominal discomfort. They are usually worst in the days after a dose increase and settle as the body adapts, which is exactly why the dose is stepped up slowly. Reduced appetite is the intended effect rather than a side effect, but it can tip into inadequate food and fluid intake.

The product information for these medicines carries specific warnings. None of them is for use in pregnancy or while trying to conceive, and treatment is stopped when a pregnancy is planned or discovered; on breastfeeding the product information differs between the products, so check the leaflet for the pen you hold. For semaglutide and tirzepatide it also recommends contraception for women of childbearing potential while treatment continues. One point about the contraceptive pill is worth correcting, because the opposite claim circulates widely: the European product information for each of these medicines concludes that the pill keeps working. In the tirzepatide study a single dose did measurably reduce the hormone exposure reached, but the product information records that the reduction is not considered clinically relevant and that no dose adjustment of oral contraceptives is required; for liraglutide it states that the contraceptive effect is anticipated to be unaffected, and for semaglutide that it is not anticipated to decrease the effectiveness of oral contraceptives. Where the tirzepatide product information does ask for monitoring is with oral medicines that have a narrow therapeutic index, such as warfarin and digoxin, at the start of treatment and after a dose increase; oral contraception is not in that group. The ordinary rule still stands: if you vomit or have severe diarrhoea soon after taking your pill, follow the leaflet for your own contraceptive. There are also warnings about acute pancreatitis, gallbladder disease, and dehydration and kidney injury after persistent vomiting. Severe or persistent abdominal pain radiating to the back needs urgent medical assessment rather than a wait.

What it costs in Ireland and what is reimbursed

These treatments are almost always paid for privately when the indication is weight management. Reported monthly costs in Ireland run roughly from 180 to 350 euro depending on the product, the dose and the pharmacy, and the dose usually rises over the first months, so the early figure is not the settled figure. The price of the medicine is set by the pharmacy that dispenses it, not by us, and we do not sell or supply medicines at all.

Reimbursement is the part people most often get wrong. The Drugs Payment Scheme caps what a household pays each month for prescribed medicines that are reimbursable, but a medicine has to be covered in the first place for the cap to apply, and GLP-1 treatment prescribed for weight management is generally not reimbursed in Ireland. The same substance prescribed for type 2 diabetes is treated differently. Ask the pharmacy to check the status of your specific prescription before you commit to a course, because that answer decides the real monthly cost.

What happens if you stop

Weight tends to come back. In the withdrawal phases of the published trials, participants who stopped treatment regained a large share of the weight they had lost, and appetite returned towards where it had been. That is not a failure of willpower; obesity behaves as a long-term condition, and these medicines treat it while they are being taken rather than curing it.

The practical consequences are worth thinking about before starting rather than after. Plan for what happens when a course ends, whether that is a maintenance dose, a structured handover to diet and activity changes that have had time to become habits, or a conversation about staying on treatment. Resistance training and adequate protein intake matter because some of the weight lost on these drugs is lean tissue. If cost is the reason a stop is coming, raise it with your prescriber early, since a planned reduction is easier to manage than an abrupt one when the pen runs out.

How our weight management assessment works

MEDINOW runs a written medical assessment for weight management priced at 29.90 euro. You complete a medical questionnaire covering height and weight, medical history, current medicines and allergies, previous weight management treatment and any relevant blood results, and a doctor reviews it. There is no video consultation, no phone appointment and no live chat; the assessment is read and answered in writing.

Where the doctor considers treatment appropriate, the prescription is issued as a PDF carrying the fields listed in the Annex to Directive 2012/52/EU and sent to you by email. You bring it to a pharmacy of your choice with photo identification. There is no PIN code and no national patient number involved, and we never name or link a particular pharmacy. A pharmacist may ask for a printed copy and always keeps professional discretion over whether to dispense. The fee covers the medical assessment itself, not the issuing of a document. If the doctor declines on medical or legal grounds, the fee is refunded. 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 refund the full amount.

Who wrote this page

This page was written by the MEDINOW editorial team and reviewed by lek. Damian Wojno, a doctor registered in Poland, PWZ no. 3211301. He is not on the Irish Medical Council register. Reviewed on 29 August 2026.

The page describes prescription-only medicines as information and is not an advertisement for any of them. It is not a diagnosis and it does not replace an assessment by a doctor who knows your history. The licensed indications, warnings and contraindications summarised here are set out in full in each product's Summary of Product Characteristics.

How this page was put together: the medicines, categories and rules described here were checked against the sources listed below rather than written from memory, and any figure we could not verify at source was left out instead of estimated. Where Irish practice differs from the rules of another country, the Irish position is the one stated on this page, and the Irish regulators named here are the HPRA for medicines, the HSE for health services, the PSI for pharmacy and the Irish Medical Council for doctors practising in Ireland. Corrections are welcome by email and are made to the page rather than argued about.