Weight Loss Injections in Belfast: What You Need to Know

What do weight loss injections do, and how are they different from each other?

Mounjaro and Wegovy share a family resemblance but work differently under the bonnet. Wegovy contains semaglutide, which activates the GLP-1 receptor, a pathway involved in appetite regulation and blood-sugar control. Mounjaro contains tirzepatide, which activates both the GLP-1 receptor and a second receptor, GIP. That dual action makes it the only medicine of its kind currently licensed for weight management in the UK.

Both slow the rate at which your stomach empties, which extends the feeling of fullness after meals. Most people find they are simply less interested in food, and portion sizes fall naturally rather than through willpower. Our page covering weight loss injections goes into the mechanism in more detail if you want a fuller picture.

In clinical trials, both medicines produced meaningful average weight reductions: the SURMOUNT-1 trial of tirzepatide recorded average body-weight reductions of around 20–21% over 72 weeks at the highest dose, while the STEP 1 trial of semaglutide 2.4mg, published in the New England Journal of Medicine, showed around 15% on average over 68 weeks. These are group averages from tightly controlled trials; individual results vary, and no outcome is guaranteed.

The injections are pre-filled pens, used once a week. Treatment always starts at the lowest dose. The starting dose for Mounjaro is 2.5mg, its job is to let your system adjust before any meaningful therapeutic effect, not to produce results in itself. Doses are increased by the prescriber over time, usually in four-week steps.

Who can get weight loss injections in Belfast, and what does the NHS offer?

Private eligibility, as set out in the licensed product specifications, is broadly: adults with a BMI of 30 or above, or 27 or above with at least one weight-related health condition. Lower BMI thresholds apply for some ethnic backgrounds under UK guidance. A BMI alone never determines suitability, the prescriber looks at the whole picture, including your medical history and any medicines you already take.

On the NHS in Belfast, access follows UK-wide commissioning criteria that are being phased in gradually. NICE recommends tirzepatide under a structured schedule tied to BMI and the number of qualifying conditions; NICE technology appraisal TA1026 sets out that guidance in full. Wegovy is recommended through specialist weight management services under a separate appraisal, with waiting lists that are commonly long across Northern Ireland and the rest of the UK. For many people in Belfast, NHS access is either not yet available to them or involves a wait of months or years.

Private treatment through a regulated online pharmacy sidesteps that wait. Prescribers review your consultation the same day; if you are clinically suitable and order before midday, treatment is dispatched the same working day. There is no local clinic appointment to book. You can explore what our treatment options include and start a free consultation from home. That said, private treatment is not for everyone, if you are unsure whether you meet NHS criteria, your GP is a good first conversation.

What should Belfast patients know about using and storing the injections day to day?

Both Mounjaro and Wegovy pens need to be kept in the fridge, most people slot them into the fridge door, which works fine as long as the temperature stays between 2°C and 8°C. Exact guidance on room-temperature windows, which differ between the two medicines, is in the Patient Information Leaflet inside your pack; always follow that rather than anything you read online.

Injection sites rotate between the abdomen, thigh and upper arm. Rotating the site each week reduces the chance of skin irritation. If you are new to self-injection, it is far less daunting than it sounds: the pens are pre-filled, and the needle is short. A question our prescribers hear regularly from new patients is whether they can bring the pen out of the fridge before bed, to take it at room temperature in the morning. The SmPC gives the specific window for this, refer to it directly.

For safe disposal, sharps bins are available from local pharmacies in Belfast, and a 1-litre sharps container can be ordered alongside your treatment if you prefer to have one to hand from day one. Used pens should never go into household recycling.

If you want a clearer sense of what to expect in the first weeks, our page on how fast weight loss injections work walks through the typical timeline honestly, including the slower early phase that catches some people off guard.

Are there any side effects Belfast patients should prepare for?

The most common side effects of both medicines are gastrointestinal: nausea, loose stools, constipation, indigestion and burping are all reported. They tend to be most noticeable in the first few weeks or after a dose increase, and many people find them manageable or short-lived. If you are considering options that act more quickly, our guide to fast weight loss injections explains what the evidence says about accelerated approaches and what to realistically expect.

The NHS medicines page for tirzepatide lists the full side-effect profile for Mounjaro and describes which symptoms to monitor. For Wegovy, the equivalent semaglutide NHS page covers the same ground. Both are worth reading before you start.

Pancreatitis is a rarer but more serious risk. Get urgent medical help if you experience severe stomach pain that radiates to your back, especially with vomiting. The MHRA highlighted this in a January 2026 Drug Safety Update for GLP-1 medicines. Any suspected side effects can be reported through the Yellow Card scheme.

These medicines are not recommended during pregnancy, while breastfeeding, or when actively trying to conceive, discuss contraception with your prescriber before starting. They are not licensed for under-18s. If you have further questions about which injection might suit you, our FAQs page covers the most common ones, including a comparison of the fastest weight loss injections currently available, and our contact page connects you with the aftercare team seven days a week. You can also read more about how a weight loss injection fits into a broader treatment plan, or find out how fast weight loss injections work so you know what to expect at each stage of your treatment.