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The honest answer is Mounjaro, with Wegovy close behind
In the UK, two injections are licensed specifically for weight loss: Mounjaro and Wegovy. Both are taken once a week with a pre-filled pen. The difference is what each one targets.
Mounjaro, or tirzepatide, acts on two gut hormones: GLP-1 and GIP. Wegovy, or semaglutide, acts on one: GLP-1. That second hormone is the main reason Mounjaro tends to shift more weight.
In the SURMOUNT-1 trial, people on the highest Mounjaro dose lost up to 20.9% of their body weight over 72 weeks. In the STEP-1 trial, people on the highest Wegovy dose lost up to 14.9% over 68 weeks. Both are strong results. Mounjaro's is simply bigger on average.
Where Wegovy still wins
Wegovy costs less month to month, which matters when you are paying privately over a year or more. It also has the longer real-world track record, having been used for weight loss before Mounjaro arrived.
Best on paper isn't best for everyone
Both injections are for adults with a BMI of 30 or more, or 27 and above with a weight-related condition like type 2 diabetes, high blood pressure, or high cholesterol. If you fall below that, neither is for you, and a good clinic will tell you so rather than sell to you.
They are also off the table if you are pregnant or breastfeeding, if you have had pancreatitis, or if you have a personal or family history of a type of thyroid cancer called medullary thyroid cancer, or a condition called MEN2.
Then there is price. Mounjaro starts at £174.99 a month and rises to £309.99 at the top dose. Wegovy starts at £129.99 and rises to £249.99. That gap is real, and for plenty of people it makes Wegovy the practical best.
Our pricing is flat, with the assessment, prescription, and cold-chain delivery all included. No hidden fees at checkout.
The best injection is the one you can stick with
Forget the leaderboard for a second. The injection that is best for you is the one that works, that you can tolerate, and that you can afford long enough to get a result.
Mounjaro and Wegovy share the same side-effect profile, mostly nausea, constipation, and a bit of stomach ache in the early weeks. Those usually settle as your body adjusts. We covered what is normal and what needs a doctor in our side effects guide.
Both start low and step up slowly, at least four weeks on each dose before moving up. Rushing it is how people end up on the bathroom floor. The medicine is not a microwave; you do not speed it up by mashing the buttons. I have watched people try exactly that, and none of them enjoyed the result.
So the honest way to define best is simple. It is the injection you can keep up, without misery, for long enough to see the result.
You find the right one through an assessment, not a bargain
Rule of thumb: the decision starts with a proper clinical assessment, not a Google search or a price that looks too good to be true.
Here is the strong opinion I will give you. The cheapest online seller is rarely the safest. A genuine pen has to travel at 2°C to 8°C from a licensed pharmacy to your door, prescribed by a GMC-registered clinician and dispensed by a GPhC-registered pharmacy. Cut corners on any of that and you are not buying medicine; you are buying a gamble.
The NHS and NICE both publish clear guidance on who these medicines are for. If a site cannot show you the basics, walk away.
Clear a spot in the fridge before your pen arrives, fill in the online assessment, and let a clinician work out which one fits. That is how you find the actual best injection for weight loss: the one prescribed for you, not the one with the loudest headline.
