What's the best weight loss injection available in the UK right now?

You're looking at two injections and want to know which one works better

Picture this: you've spent an hour reading about weight loss injections, you've seen Mounjaro and Wegovy mentioned everywhere, and you still can't get a straight answer. Here it is. In the UK, two injectable medicines are licensed specifically for weight management in adults: tirzepatide, sold as Mounjaro by Eli Lilly, and semaglutide, sold as Wegovy by Novo Nordisk. Nothing else is licensed for this purpose in injection form. So when people ask what's the best weight loss injection, the real question is which of these two fits their situation.

Tirzepatide works differently from semaglutide. It activates both the GIP and GLP-1 receptors, two gut hormones involved in appetite signalling and blood-sugar regulation. Semaglutide targets GLP-1 alone. That dual mechanism is part of why tirzepatide's trial numbers look stronger. In SURMOUNT-1, participants on the highest tirzepatide dose lost around 20–21% of their body weight on average over 72 weeks, as reported in the New England Journal of Medicine. Semaglutide at its standard 2.4mg maintenance dose produced around 15% average loss in the STEP 1 trial over 68 weeks. Both numbers are meaningful; tirzepatide's are larger. You can read more about the specific evidence behind each on our most effective weight loss injection page.

Wegovy also now comes in a 7.2mg dose, approved by the MHRA in January 2026 and available in a dedicated single-dose pen from April 2026, which narrows the gap in average results. Even so, in a direct comparison (the SURMOUNT-5 open-label trial published in 2025) tirzepatide still produced greater average weight reduction than semaglutide 2.4mg. The gap is real, though both are far more effective than lifestyle changes alone.

What's actually in these injections, and why that matters for day-to-day use

Both Mounjaro and Wegovy are pre-filled subcutaneous injection pens, used once a week. You inject into the abdomen, thigh or upper arm, rotating the site each time. Neither requires any mixing or preparation, the pen comes ready to use. Storage is in the fridge at 2–8°C; the exact room-temperature window if you're travelling is in each medicine's Patient Information Leaflet and worth reading before any trip. A sharps container is required for safe disposal of used pens.

The starting doses are low by design. Mounjaro begins at 2.5mg, not because that dose does the heavy lifting, but because it gives your system time to adjust before the prescriber increases it. Wegovy starts at 0.25mg for the same reason. Jumping straight to the higher doses would increase the likelihood of nausea and vomiting significantly. Titration is managed by your prescriber, typically in four-week steps, and decisions about when to increase are based on how you're tolerating the current dose, not a fixed calendar.

Side effects for both are predominantly gastrointestinal: nausea, indigestion, loose stools, constipation and burping are the most commonly reported. They tend to peak after starting or stepping up, then ease. The NHS medicines pages for tirzepatide and semaglutide give a full, plain-English rundown of what to watch for. If you experience severe, persistent stomach pain that reaches the back (with or without vomiting) seek urgent medical advice; the MHRA flagged acute pancreatitis as a known infrequent but serious risk in its January 2026 Drug Safety Update. Our safest weight loss injection page covers the full safety picture in detail.

Who can use these injections, and what the licensing actually says

Both medicines are licensed for adults with a BMI of 30 or above, or a BMI of 27 or above alongside at least one weight-related health condition, things like high blood pressure, type 2 diabetes, high cholesterol or obstructive sleep apnoea. Lower BMI thresholds apply for some ethnic backgrounds under UK clinical guidance. BMI alone doesn't settle the question; a prescriber looks at your full health picture, including any medicines you already take and conditions that might rule one treatment out.

Neither is licensed for anyone under 18, and neither is recommended during pregnancy, while breastfeeding, or when trying to conceive. Women using the oral contraceptive pill and starting tirzepatide should add a non-oral contraceptive method for the first four weeks of treatment and for four weeks after each dose increase, because tirzepatide can reduce how well the pill is absorbed. NHS guidance does not flag the same interaction for semaglutide, but discuss your contraception with your prescriber before starting either. Our page on injections and diabetes explains the separate considerations for people with type 1 diabetes.

If you're wondering about NHS access, NICE recommends tirzepatide under TA1026 for eligible adults within a phased NHS rollout that is still expanding in 2026. The criteria are strict. Private prescription through a regulated pharmacy is the route most people are currently using if they don't meet the NHS thresholds or don't want to wait.

How to choose, and what comes next if you want to start

There is no universally best weight loss injection. Tirzepatide's trial evidence is stronger on average weight loss. Semaglutide has a longer real-world track record and, at 7.2mg, is approaching similar territory. Some people do better on one than the other for reasons that aren't fully predictable in advance, prior response, tolerability, other health conditions and medicines all play a part. That is precisely what a prescriber works through with you.

Our weight loss injections overview explains both options side by side in more detail, and the named injection for weight loss page covers what these medicines are called and how they differ from diabetes injections like Ozempic, which is not licensed for weight loss. If cost is part of your thinking, the cost of weight loss injections page sets out what private treatment typically involves. At nume, a named GPhC-registered prescriber reads your consultation personally, order by 12pm on a weekday and, if you're clinically suitable, your prescription is reviewed the same day. Check your eligibility with a free consultation.