One of the most common questions we get asked: “What’s the best injection for weight loss?”
It’s an understandable question. Injectable weight loss medicines have exploded in recent years and continue to evolve. With treatments like Wegovy and Mounjaro widely discussed, and new options on the horizon, many people want to know which option is best.
The honest answer is that there isn’t a single “best” injection for everyone. The right treatment is one that’s clinically appropriate for you, based on your health history, how your body responds, and what feels manageable long term.
Here we break down the options currently available, what’s recently changed, and how to think about choosing between them.
What weight loss injections are available in the UK?
There are currently two injectable drugs licensed for weight loss in the UK that you’ve probably heard of already: Wegovy (semaglutide) and Mounjaro (tirzepatide).
Both these medicines work by slowing digestion, tricking your brain into feeling more satisfied with smaller portions, and helping you feel fuller for longer. However, they are not a shortcut or “cheat” to lose weight. They’re tools that should be used alongside healthy eating and exercise to help you achieve gradual, sustainable results.
Wegovy (semaglutide)
Wegovy contains a medicine called semaglutide, a GLP-1 receptor agonist. It works by mimicking a natural hormone called GLP-1, which your body produces after eating to help regulate hunger.
Wegovy is taken once weekly and follows a gradual dose-escalation schedule, meaning that you start on a low dose and gradually increase until you reach a maintenance level. Doses typically increase every four weeks, assuming you are tolerating the current dose well.
As of January 2026, the highest dose of Wegovy contains 7.2mg of semaglutide. However, not everyone needs the highest dose. The best dose is one that supports weight loss while keeping side effects manageable. For many people, this is achieved at 1.7mg or 2.4mg doses.
Mounjaro (tirzepatide)
Mounjaro works slightly differently. It targets two hormone pathways, GLP-1 and GIP, which give it a slightly broader effect in the body. Alongside helping you feel fuller for longer, it influences:
Appetite regulation
Blood sugar levels
Energy storage.
Like Wegovy, Mounjaro is injected once weekly and gradually increased over time to a maintenance dose. The same principle applies: the goal is not to reach the highest dose. It’s to find the lowest effective dose that works for your body and supports your weight loss goals.
So, which one works better?
Wegovy and Mounjaro both have shown to lead to substantial, sustained weight loss.
Some clinical trials suggest that the dual action of Mounjaro might give it a slight edge over Wegovy, helping people lose a higher percentage of their body weight on average (1). However, when comparing the new highest dose of Wegovy, the overall outcomes aren’t too dissimilar:
People taking 7.2mg of Wegovy lost an average of 18.7% of their starting body weight over 72 weeks, with half of all participants losing 20% or more (2).
People taking 15mg of Mounjro lost an average of 22.5% of their starting body weight over 72 weeks, with 63% of all participants losing 20% or more. (3)
Taking these figures alone, Mounjaro still slightly outperforms Wegovy in the amount of weight lost on average in clinical trials. But it’s important to remember that these results are averages and aren’t necessarily a reflection of how much weight you’ll lose on either medicine in real life.
Everyone responds to medicines differently. Some people respond better to one weight loss injection than the other. Others tolerate one more comfortably. There isn’t a universal winner.
What actually makes an injection the “best”?
Rather than asking which injection is best overall, it’s more helpful to ask: “Which weight loss injection is best for me?” And the answer will depend on four basic factors:
1. Medical history
Reviewing your medical history is the most important starting point. Neither semaglutide (Wegovy) nor tirzepatide (Mounjaro) are suitable for everyone. They shouldn’t be used if you have:
A personal or family history of medullary thyroid carcinoma (MTC)
A condition called Multiple Endocrine Neoplasia type 2 (MEN 2)
You should also tell your prescriber if you’ve ever had:
Pancreatitis or ongoing pancreas problems
Significant kidney issues
Diabetic retinopathy
Severe gastrointestinal disease
That doesn’t automatically mean you can’t receive treatment, but it does mean your clinician needs to assess carefully. For some people, injectable GLP-1 or dual-agonist medicines simply aren’t the safest option. In those cases, other weight management approaches may be more appropriate.
Takeaway: The “best” treatment is always the one that fits your medical profile safely.
2. Side effect tolerance
Wegovy and Mounjaro share common GLP-1 side effects, particularly when starting or increasing the dose. These can include:
Nausea
Constipation
Diarrhoea
Bloating
Fatigue
For many people, these symptoms are mild and improve as the body gets used to the medicine.
However, even though the side effect profiles overlap, individual experiences can differ. Some people feel better on semaglutide. Others find that tirzepatide suits them more comfortably. Sometimes the best injection is simply one that you feel better taking.
Takeaway: The “best” treatment is the one that your body handles more smoothly
3. Weight loss goals
Both injections are licensed to treat weight loss for people with a BMI of 30 or higher, or over 27 if you have a weight-related health condition.
Some people with higher BMIs or more ambitious weight loss goals may be drawn towards Mounjaro, as it has performed better (in terms of weight loss) in clinical trials. But it’s important to remember that trial results are averages, not guarantees.
The goal isn’t to chase the biggest percentage, but to find the right balance between effectiveness and tolerability. For many people, steady, sustainable progress at a lower dose is far more valuable than pushing for maximum weight loss.
Takeaway: The “best” treatment achieves slower, sustainable weight loss, not fast results.
4. Existing health conditions
Your wider health picture can also influence which injection may suit you best. For example:
Mounjaro (tirzepatide) is licensed for type 2 diabetes as well as weight management. Because it targets both GLP-1 and GIP receptors (with GIP involved in insulin regulation), it may be a logical option for people managing blood sugar issues alongside weight loss.
Wegovy (semaglutide) has been approved to reduce the risk of major cardiovascular events in people with obesity and heart disease. In clinical studies, it reduced the risk of heart attack by around 20% (4). It’s also licensed to treat pain from knee osteoarthritis.
This doesn’t mean choosing between the two injections is black and white. Semaglutide can still be used to treat type 2 diabetes (brand name Ozempic). Likewise, Mounjaro offers cardiovascular benefits and has recently been approved as a treatment for sleep apnea.
Still, finding which one aligns best with your overall health profile is crucial.
Takeaways: The “best” treatment aligns with your wider health conditions.
What’s next in injectable treatments?
At the moment, choosing the best weight loss injection for you means deciding between Mounjaro and Wegovy. But there is another new medication currently in development called Retatrutide.
Retatrutide is another once-weekly injection that has been labelled a “game changer in obesity” (5). It targets three hormonal pathways (GLP-1, GIP, and glucagon), and clinical trials show huge promise. In the latest study, people lost an average of 28.7% of their body weight in 68 weeks (6).
But this doesn’t necessarily make it the “best” weight loss injection.
Several people dropped out of the study as they were losing too much weight. The drug isn’t yet a licensed or approved option outside of clinical trials, but this goes to show that even when it does come to market, it won’t be the best or necessarily even a safe option for everyone.
The real definition of “best”
If you’re comparing weight loss injections, it’s natural to want a clear winner. But the truth is, the best weight loss injection is the one that’s clinically appropriate for you.
Both Wegovy and Mounjaro are effective options. If retatrutide passes development, it could be another option in the future. But the right choice is the one that:
Fits your medical history
Is safe for you
Feels tolerable
Supports meaningful, sustainable weight loss
Aligns with your wider health goals
That’s why a proper clinical review matters. If you’re unsure which weight loss injectable may suit you, our independent doctors can review your medical history and guide you towards a treatment that makes sense for your individual needs or give you advice on switching treatments.
Weight loss treatment works best when it’s personalised, not chosen based on averages alone.
👉 Explore our weight loss injections or complete a consultation for personalised advice.
References
Aronne LJ, Horn DB, le Roux CW, Ho W, Falcon BL, Gomez Valderas E, et al. Tirzepatide as Compared with Semaglutide for the Treatment of Obesity. New England Journal of Medicine [Internet]. 2025 May 11;393(1).
Wharton S, Freitas P, Jøran Hjelmesæth, Kabisch M, Kandler K, Ildiko Lingvay, et al. Once-weekly semaglutide 7·2 mg in adults with obesity (STEP UP): a randomised, controlled, phase 3b trial. The Lancet Diabetes & Endocrinology [Internet]. 2025 Sep 1.
Eli Lilly and Company Lilly’s tirzepatide delivered up to 22.5% weight loss in adults with obesity or overweight in SURMOUNT-1 [Internet]. investor.lilly.com. 2022 Apr 28.
A. Michael Lincoff, Kirstine Brown‐Frandsen, Colhoun HM, Deanfield J, Emerson SS, Sille Esbjerg, et al. Semaglutide and Cardiovascular Outcomes in Obesity without Diabetes. The New England Journal of Medicine [Internet]. 2023 Nov 11;389(24).
Katsi V, Koutsopoulos G, Fragoulis C, Dimitriadis K, Tsioufis K. Retatrutide—A Game Changer in Obesity Pharmacotherapy. Biomolecules. 2025 May 30;15(6):796.
Eli Lilly and Company. Lilly’s triple agonist, retatrutide, delivered weight loss of up to an average of 71.2 lbs along with substantial relief from osteoarthritis pain in first successful Phase 3 trial | [Internet]. investor.lilly.com. 2025 Dec 11.