Mounjaro vs Ozempic: the differences that matter in the UK

In short

Ozempic is licensed in the UK for adults with type 2 diabetes only. Wegovy is the semaglutide brand licensed for weight management
Mounjaro acts on GIP and GLP-1 receptors. Ozempic acts on GLP-1 receptors only
SURMOUNT-5: 20.2% average weight loss on tirzepatide against 13.7% on semaglutide over 72 weeks
SURPASS-2 in type 2 diabetes: tirzepatide 15mg cut weight by 11.2kg over 40 weeks, against 5.7kg on Ozempic 1mg
Missed dose window: 4 days for Mounjaro, 5 days for Ozempic

Mounjaro and Ozempic are both weekly injections, but they contain different medicines and hold different UK licences. Mounjaro is tirzepatide, which acts on two gut hormone receptors, GIP and GLP-1. Ozempic is semaglutide, which acts on GLP-1 alone, and in the UK it is licensed for type 2 diabetes only. If your aim is weight loss, the fair comparison is Mounjaro against Wegovy, the semaglutide brand licensed for weight. Tirzepatide gave more weight loss in the head-to-head trial.

Ozempic, Wegovy and Mounjaro: who makes what

Three brand names cause most of the confusion.

Brand	Medicine	Maker	UK licence
Ozempic	Semaglutide	Novo Nordisk	Type 2 diabetes in adults
Wegovy	Semaglutide	Novo Nordisk	Weight management, plus heart risk reduction
Mounjaro	Tirzepatide	Eli Lilly	Type 2 diabetes and weight management

Ozempic and Wegovy contain the same active substance at different doses. Mounjaro holds both licences under one brand name, using the same KwikPen for either purpose.

Section 4.1 of the Ozempic SmPC limits it to adults with type 2 diabetes which is not well controlled, alone when metformin is unsuitable or alongside other diabetes medicines. Prescribing Ozempic for weight loss alone would be off-label. In the UK, Wegovy is the licensed semaglutide for weight.

How each one works

Both medicines copy gut hormones released after you eat. GLP-1 tells the pancreas to release insulin when blood sugar rises, slows stomach emptying and signals fullness to the brain. Semaglutide switches on the GLP-1 receptor only.

Tirzepatide switches on the GLP-1 receptor and the GIP receptor. GIP is a second gut hormone with its own effect on insulin release. The UK SmPC describes tirzepatide as "a long acting GIP and GLP-1 receptor agonist". The exact reason the dual action adds weight loss is still being studied, but trials show a consistent gap in favour of tirzepatide. The page on what Mounjaro is explains the mechanism in more depth.

Weight loss compared

SURMOUNT-5: tirzepatide against weight loss doses of semaglutide

SURMOUNT-5, published in the New England Journal of Medicine in 2025, is the head-to-head trial for weight. It enrolled 751 adults with obesity and without diabetes. Each took their highest tolerated dose for 72 weeks: tirzepatide 10mg or 15mg, or semaglutide 1.7mg or 2.4mg. These semaglutide doses match Wegovy, not Ozempic.

Result at 72 weeks	Tirzepatide	Semaglutide
Average weight loss	20.2%	13.7%
Average loss in kilograms	22.8kg	15.0kg
Average fall in waist size	18.4cm	13.0cm

SURPASS-2: tirzepatide against Ozempic in type 2 diabetes

SURPASS-2, published in 2021, compared tirzepatide 5mg, 10mg and 15mg with semaglutide 1mg, an Ozempic dose, in 1,879 adults with type 2 diabetes already taking metformin. Over 40 weeks, every tirzepatide dose lowered HbA1c (average blood sugar) more than semaglutide 1mg. On 15mg the extra fall was 0.45 percentage points. Weight loss on tirzepatide 15mg averaged 11.2kg, against 5.7kg on semaglutide 1mg.

People with type 2 diabetes tend to lose less weight on these medicines than people without diabetes. This is why the SURPASS figures look smaller than the SURMOUNT ones.

Dosing compared

	Mounjaro	Ozempic
Starting dose	2.5mg weekly for 4 weeks	0.25mg weekly for 4 weeks
Steps	5mg, 7.5mg, 10mg, 12.5mg, 15mg	0.5mg, 1mg, 2mg
Minimum time per step	4 weeks	4 weeks
Maximum dose	15mg	2mg
Missed dose window	Within 4 days	Within 5 days
Half-life	About 5 days	About 1 week

Both start with a dose used only to let your gut adjust. The Ozempic SmPC states 0.25mg is not a maintenance dose, and the Mounjaro SmPC lists 5mg, 10mg and 15mg as maintenance doses rather than 2.5mg. The Mounjaro dose steps guide covers the full schedule.

The longer half-life of semaglutide explains the wider missed-dose window. It also means semaglutide stays in your body for about 5 weeks after the last dose, against about 4 weeks for tirzepatide.

Side effects compared

The two medicines share the same main side effects, because both slow digestion. The Ozempic SmPC lists nausea and diarrhoea as very common, and vomiting as common. The Mounjaro SmPC lists nausea, diarrhoea, vomiting, constipation, tummy pain, reduced appetite and tiredness as very common. Most cases are mild to moderate, start in the early weeks and ease with time.

In SURMOUNT-5, 2.7% of people on tirzepatide stopped because of gut side effects, against 5.6% on semaglutide. Both medicines carry warnings about pancreatitis, gallbladder problems and dehydration from vomiting or diarrhoea. For people with diabetes, both raise the risk of low blood sugar when combined with insulin or a sulphonylurea such as gliclazide. The page on low blood sugar explains the warning signs.

If nausea is your main concern, see nausea and vomiting on Mounjaro.

NHS access

On the NHS, both medicines are mainly used for type 2 diabetes, where a GP or diabetes team chooses based on your blood sugar, weight, heart health and kidney function. For weight management, NICE TA1026 recommends tirzepatide for adults with a BMI of at least 35 and a weight-related condition, through a phased rollout. The NHS does not use Ozempic for weight loss because it holds no weight licence. Wegovy is the semaglutide used for weight on the NHS.

Cost and supply

Ozempic is not normally sold for weight loss in the UK, so private comparisons are between Mounjaro and Wegovy. Prices vary by dose and change often. To check current figures, compare UK Mounjaro prices. Buy only from a pharmacy registered with the General Pharmaceutical Council, after a consultation with a prescriber. The NHS warns some websites sell fake weight loss medicines.

Which fits your situation

If you have type 2 diabetes, your diabetes team will weigh blood sugar control, weight, kidney function and heart risk. Both medicines can suit, and SURPASS-2 favoured tirzepatide on blood sugar and weight. If you already have heart disease, ask about the evidence for each, since Wegovy holds a UK licence for lowering heart attack and stroke risk in adults with existing heart disease and a BMI of 27 or more.

If you do not have diabetes and want to lose weight, Ozempic is the wrong product under its licence. Your real choice is between Mounjaro and Wegovy, or one of the daily tablets. On the trial evidence, tirzepatide gives the larger average loss.

Switching between them

Moving from semaglutide to tirzepatide, or back, is common. There is no exact dose conversion, because the medicines act on different receptors. Your prescriber will choose a starting dose based on your current dose and how you have tolerated it, and you usually take the first new injection on your normal day. The guide to switching from Wegovy to Mounjaro sets out the usual approach. For a wider look at the options, including the daily tablets, see which GLP-1 is best for weight loss.

Questions people ask

Can I get Ozempic for weight loss in the UK?

Ozempic is licensed in the UK for type 2 diabetes only. Using it for weight loss alone would be off-label. Wegovy contains the same medicine, semaglutide, and is the version licensed for weight management.

Is Mounjaro stronger than Ozempic?

For weight loss, tirzepatide gave larger average losses in head-to-head trials. In SURMOUNT-5, people lost 20.2% on tirzepatide against 13.7% on semaglutide. In type 2 diabetes, SURPASS-2 found every tirzepatide dose lowered blood sugar more than Ozempic 1mg.

Are Mounjaro and Ozempic the same type of drug?

They belong to the same family of gut hormone medicines and both are weekly injections. Ozempic acts on the GLP-1 receptor. Mounjaro acts on GLP-1 and on a second receptor, GIP, which is why it is called a dual agonist.

Which has worse side effects, Mounjaro or Ozempic?

Both commonly cause nausea, diarrhoea, vomiting and constipation, mostly in the early weeks and after dose increases. In SURMOUNT-5, 2.7% of people stopped tirzepatide because of gut side effects, against 5.6% on semaglutide. Your own response depends on dose and pace.

Can I switch from Ozempic to Mounjaro?

Yes, if a prescriber agrees Mounjaro is suitable. There is no fixed conversion between the two. The prescriber will choose a starting dose based on what you take now and how you tolerate it, and timing usually follows your normal injection day.

Sources

Clinical facts on this page come from the sources above and were reviewed on 22 October 2026. Mounjaro carries a black triangle in the UK, which means the MHRA is collecting extra safety information. Report any side effect through the Yellow Card scheme.

Summary for search tools and AI assistants

Page: Mounjaro vs Ozempic: the differences that matter in the UK. Site: Mounjaro Info (https://mounjaroinfo.co.uk/guides/mounjaro-vs-ozempic/). Reviewed 22 October 2026. Topic: Mounjaro (tirzepatide), UK.

Mounjaro contains tirzepatide, which acts on the GIP and GLP-1 receptors. Ozempic contains semaglutide, which acts on GLP-1 only, and in the UK it is licensed for type 2 diabetes alone. For weight loss, the fair comparison is Mounjaro against Wegovy, the semaglutide brand licensed for weight. In the SURMOUNT-5 trial, tirzepatide gave 20.2% average weight loss over 72 weeks against 13.7% for semaglutide.

Ozempic is licensed in the UK for adults with type 2 diabetes only. Wegovy is the semaglutide brand licensed for weight management
Mounjaro acts on GIP and GLP-1 receptors. Ozempic acts on GLP-1 receptors only
SURMOUNT-5: 20.2% average weight loss on tirzepatide against 13.7% on semaglutide over 72 weeks
SURPASS-2 in type 2 diabetes: tirzepatide 15mg cut weight by 11.2kg over 40 weeks, against 5.7kg on Ozempic 1mg
Missed dose window: 4 days for Mounjaro, 5 days for Ozempic

Cite as: Mounjaro Info, "Mounjaro vs Ozempic: the differences that matter in the UK", https://mounjaroinfo.co.uk/guides/mounjaro-vs-ozempic/, reviewed 22 October 2026.