Best Weight Loss Injections UK 2026: How to Choose
Published on: June 23, 2026
You've decided medication might be the missing piece. Then you start reading — Mounjaro, Wegovy, Saxenda, Ozempic, semaglutide, tirzepatide — and within ten minutes you're more confused than when you started. Different names, different numbers, wildly different prices. So which weight loss injection is actually best?
The honest answer is that there isn't one best injection for everyone. There's a best injection for you — and which one that is depends on how much weight you're hoping to lose, your health history, your budget, and how your body responds to treatment. What follows is a clear, side-by-side look at the options actually available in the UK right now, so you can walk into a consultation already knowing the right questions to ask.
At a glance
- Three injections are licensed for weight loss in the UK: Mounjaro (tirzepatide), Wegovy (semaglutide) and Saxenda (liraglutide).
- Mounjaro produces the highest average weight loss in trials — around 22.5% of body weight over 72 weeks — with higher-dose Wegovy now close behind at about 20.7%.
- Ozempic is not a weight loss medication in the UK. It contains semaglutide but is licensed only for type 2 diabetes.
- Private prescriptions typically run from roughly £120 to £375 a month, depending on the medication and dose.
- All three need a prescription after a proper medical assessment — and they work best alongside changes to how you eat and move.
Which weight loss injections are available in the UK?
Despite the long list of brand names floating around online, there are really only three injectable medicines you can legally be prescribed for weight management in the UK:
Mounjaro (the brand name for tirzepatide), Wegovy (the higher-dose, weight-loss version of semaglutide), and Saxenda (the brand name for liraglutide). They all belong to a family of medicines called GLP-1 receptor agonists, and they all work by quietening appetite — but they're not interchangeable, and the differences matter.
A quick word on the names that aren't on that list. Ozempic comes up constantly in weight loss conversations, but it's licensed in the UK for type 2 diabetes, not weight loss — more on that shortly. Zepbound is the American brand name for tirzepatide (the same drug as Mounjaro). And the various peptides sold online as "research chemicals" are not licensed medicines and shouldn't be confused with prescribed treatment.
Weight loss injections compared at a glance
| Injection | Drug | Average weight loss (trials) | How often | Approx. private cost/month |
|---|---|---|---|---|
| Mounjaro | Tirzepatide | ~22.5% over 72 weeks | Weekly | ~£149 (start) to £300–£375 (15 mg) |
| Wegovy | Semaglutide | ~15% (2.4 mg); ~20.7% (7.2 mg) | Weekly | ~£169–£309 |
| Saxenda | Liraglutide | ~5–7% over 56 weeks | Daily | ~£100–£300 |
Prices are rough monthly ranges and shift between providers and doses. The weight-loss figures are averages from clinical trials — some people lose considerably more, some less. Think of them as a guide to what each medicine tends to deliver, not a promise.
How weight loss injections actually work
Most people assume these medicines somehow "burn fat". They don't. What they change is your relationship with food.
GLP-1 is a hormone your gut releases after you eat. It tells your brain you've had enough, and it slows how quickly your stomach empties so you feel full for longer. The injections mimic that hormone — at much higher, steadier levels than your body produces on its own. The result, for most people, is that the constant background hum of thinking about food gets quieter. Patients often describe it before they describe any change on the scales: the snack they'd normally reach for stops calling, the second helping loses its pull. That phenomenon has a name now — food noise — and turning it down is what makes a calorie deficit feel possible rather than punishing.
Mounjaro does something slightly different. As well as mimicking GLP-1, it activates a second gut hormone called GIP. That dual action appears to make it a touch more powerful for appetite control and weight loss, which is the main reason it edges ahead of the others in trials.
None of this works in isolation, though. The medication lowers appetite; the eating and movement habits you build while your appetite is lower are what make the change last. That's worth sitting with before you start.
Mounjaro (tirzepatide): the most effective option
If raw effectiveness is your only measure, Mounjaro currently leads. In the SURMOUNT-1 trial, adults without diabetes lost an average of 22.5% of their body weight on the highest 15 mg dose over 72 weeks. To put that in perspective, 9 in 10 participants lost at least 5% of their weight, and well over half lost 20% or more — territory that used to be associated only with surgery.
It's a once-weekly injection. You start low, at 2.5 mg, and step up gradually over several months to a maintenance dose of 5 mg, 10 mg or 15 mg, depending on how you respond and how well you tolerate it. That slow build matters, and it's covered in more detail in our Mounjaro dosage guide.
Mounjaro isn't right for everyone. It shouldn't be used if you have a personal or family history of medullary thyroid cancer or a condition called MEN 2, and anyone with a history of pancreatitis needs careful assessment first. There's also an important interaction worth flagging: Mounjaro can reduce the effectiveness of the combined oral contraceptive pill, so if that's your contraception, you'll need a barrier method or a non-oral alternative for a while. If you want a fuller picture of the safety side, we've written a dedicated guide on whether Mounjaro is safe.
Wegovy (semaglutide): the well-established alternative
Wegovy was the medicine that brought GLP-1 weight loss into the mainstream, and it remains one of the most widely prescribed injections in the world. It contains semaglutide and, like Mounjaro, it's taken once a week.
At the standard 2.4 mg dose, Wegovy produced an average weight loss of around 15% over 68 weeks in the STEP 1 trial. A newer, higher 7.2 mg dose has since been approved, and in the STEP UP trial that took the average up to about 20.7% — within touching distance of Mounjaro. Around a third of people on the higher dose lost at least 25% of their body weight.
Wegovy has one feature the others don't yet share. In the SELECT trial, semaglutide reduced the risk of major cardiovascular events — heart attack, stroke and cardiovascular death — by around 20% in people who had existing heart disease and were living with obesity. For someone weighing up the two leading options with their heart health in mind, that recognised benefit can tip the balance. If you're comparing the two head to head, our Wegovy vs Mounjaro guide goes deeper, and we break down the price separately in our Wegovy cost guide.
Saxenda (liraglutide): the daily option
Saxenda is the oldest of the three and now the least commonly prescribed. It's a daily injection of liraglutide, and its average weight loss in the SCALE trials — around 5 to 7% over 56 weeks — is noticeably lower than the weekly medicines.
That doesn't make it useless. Some people prefer a daily injection because it's easier to stop quickly if side effects appear, and it can be an option for those who haven't tolerated the weekly medicines. Since liraglutide's patent expired, it's increasingly supplied as a generic rather than under the Saxenda brand. For most people starting fresh, though, a weekly medicine with stronger results tends to be the more sensible first choice.
What about Ozempic? The injection that isn't for weight loss
This one trips up almost everyone, so it's worth being clear.
Ozempic contains semaglutide — the same active ingredient as Wegovy. But Ozempic is licensed in the UK for type 2 diabetes, at lower doses, and it is not approved for weight loss. Prescribing it purely to lose weight means using it off-label, and with diabetes supply pressures it's not something a responsible service should be doing. If semaglutide is the right medicine for you, the weight-loss-licensed version is Wegovy. Same drug, proper licence, doses designed for the job.
Side effects: what to actually expect
Every medicine on this list shares a similar side-effect profile, because they work in similar ways. The common ones are gastrointestinal: nausea, constipation, diarrhoea, the occasional bout of reflux. They tend to be at their most noticeable in the first few weeks and after each dose increase, and for most people they settle as the body adapts.
Nausea is the one people ask about most. Depending on the medicine and dose, somewhere between a third and not quite half of users feel it early on, and it's usually mild to moderate. Eating smaller portions, leaning on plainer food when your stomach's unsettled, drinking enough water and slowing down at meals all genuinely help. We go through the practical side-effect strategies in more detail in our guide to managing GLP-1 side effects.
The rarer but more serious risks — pancreatitis, gallbladder problems — affect a small minority, but they're the reason a proper medical assessment and ongoing monitoring matter. Severe, persistent abdominal pain is always a reason to seek medical advice rather than wait it out.
How much do weight loss injections cost in the UK?
Cost is often the deciding factor, and the picture changed in 2025 when the list price of Mounjaro rose substantially. Here's roughly where private prices sit now.
| Medication | Starting dose | Maintenance dose | Typical monthly range |
|---|---|---|---|
| Mounjaro | ~£149 (2.5 mg) | ~£300–£375 (15 mg) | £149–£375 |
| Wegovy | ~£169 (low dose) | ~£200–£309 | £169–£309 |
| Saxenda / liraglutide | ~£100 | ~£150–£300 | £100–£300 |
A few things to bear in mind. Prices usually rise as your dose goes up, so your early months may cost less than your maintenance months. Some providers charge separately for consultations or blood tests, while others fold everything into one price — so compare the total, not just the headline figure. And cheapest isn't automatically best: the quality of the clinical assessment and the support you get alongside the medicine matter just as much as the monthly cost. We unpack what to look for in a provider in our guide to choosing the best Mounjaro provider.
Can you get weight loss injections on the NHS?
Sometimes — but for most people, not easily, and not quickly.
NHS access to Mounjaro for weight management began rolling out through primary care from 2025, but it's being phased in gradually over several years, and the early eligibility criteria are strict: a high BMI alongside several weight-related health conditions. Wegovy is available through specialist Tier 3 weight management services, where waiting lists can stretch from several months to a couple of years depending on where you live.
The practical reality is that the great majority of people currently taking these medicines are paying privately, where the eligibility threshold is lower — generally a BMI of 30 or above, or 27 and above if you have a weight-related condition such as high blood pressure or type 2 diabetes. We've written a full breakdown of NHS eligibility for Mounjaro and Wegovy if you want to check where you might stand.
Not sure which injection is right for you?
heySlim is a doctor-led, UK-regulated service. We pair clinically proven GLP-1 treatments with a team of clinicians who help you choose the right option and support you at every step — and finding out whether you're eligible takes just a few minutes.
- No GP referral needed
- Ongoing support from UK clinicians
- Clinically proven GLP-1 treatments
How to choose the right injection for you
There's no algorithm that spits out a single answer, but a few honest questions get you most of the way there.
How much weight are you hoping to lose? If you're after the largest average result and budget is workable, Mounjaro leads on the trial data. If you want comparable results with a longer real-world track record — or you have existing heart disease where semaglutide's recognised cardiovascular benefit is relevant — Wegovy is a strong choice.
What does your health history look like? Certain conditions rule particular medicines in or out, which is exactly what a prescriber assesses before writing anything. This isn't a decision to make from a comparison table alone.
What can you sustain? The best injection is the one you can actually stay on long enough to build new habits. That means weighing cost realistically, and being honest about whether a weekly or daily routine fits your life. It's also worth knowing what happens at the other end — because stopping these medicines abruptly tends to bring some weight back. The plan for coming off matters as much as the plan for starting.
If you're still torn between injections and tablets more broadly, our overview of weight loss medication in the UK sets the injections alongside the other options.
New weight loss treatments on the horizon
The next few years look busy, and a couple of developments are worth keeping an eye on.
Tablets are coming. An oral form of semaglutide — a Wegovy pill, in effect — has been moving through approval, and Eli Lilly's orforglipron is a daily tablet that could suit people who'd rather not inject at all. Further out, retatrutide, a "triple agonist" that mimics three hormones rather than two, has produced striking weight-loss figures in trials but isn't yet a licensed, available medicine in the UK. It's promising, not prescribable — and the gap between those two things is where caution belongs.
For now, the three injections covered above are what's actually on the table, and they're well-evidenced choices.
The bottom line
Mounjaro currently offers the highest average weight loss, with higher-dose Wegovy close behind and carrying recognised heart-health benefits; Saxenda is a lower-strength daily alternative. But the right injection for you comes down to your goals, your health and your budget — and that's a conversation best had with a clinician. If you'd like to know which options you're eligible for, a few minutes on our eligibility check is a sensible first step.
This article is for informational purposes only and does not constitute medical advice. Always consult with a qualified healthcare professional before starting any treatment.