Mounjaro (tirzepatide) produces more weight loss than Wegovy (semaglutide) at standard doses, but Wegovy is cheaper, has stronger cardiovascular evidence, and is more widely available on the NHS. Both are once-weekly injections approved for weight management in the UK, and both work by mimicking gut hormones that reduce appetite and slow digestion. Here is everything you need to know to compare them properly.
In this article
- How do Wegovy and Mounjaro work?
- Which one delivers more weight loss?
- What are the side effects of each?
- What are the dosage schedules?
- How much do they cost in the UK?
- Can you get them on the NHS?
- Which has better heart health evidence?
- How to decide which is right for you
- Frequently asked questions
How do Wegovy and Mounjaro work?
Both medications belong to a class of drugs called incretin mimetics. They copy the action of natural gut hormones that your body releases after eating, telling your brain you are full, slowing stomach emptying, and helping regulate blood sugar.
The key difference is in the hormones they target:
- Wegovy (semaglutide) is a GLP-1 receptor agonist. It mimics one hormone, glucagon-like peptide-1 (GLP-1), which suppresses appetite, stimulates insulin release, and reduces glucagon secretion.
- Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist. It mimics two hormones: GLP-1 and glucose-dependent insulinotropic polypeptide (GIP). This dual action appears to produce a broader metabolic signal, which may explain the greater weight loss seen in clinical trials.
Both are administered by self-injection using a pre-filled pen, once per week, on the same day each week. Neither is a "magic bullet." Clinical trial participants using both drugs also followed reduced-calorie diets and increased their physical activity.
Which one delivers more weight loss?
At their standard maximum doses, Mounjaro produces more weight loss than Wegovy. Here is what the major clinical trials found:
| Trial | Drug & dose | Duration | Average weight loss |
|---|---|---|---|
| STEP 1 | Wegovy 2.4 mg | 68 weeks | 14.9% |
| STEP UP | Wegovy 7.2 mg | 72 weeks | 20.7% |
| SURMOUNT-1 | Mounjaro 15 mg | 72 weeks | 20.9% |
| SURMOUNT-5 (head-to-head) | Mounjaro 15 mg vs Wegovy 2.4 mg | 72 weeks | 20.2% vs 13.7% |
The SURMOUNT-5 trial is the only direct head-to-head comparison. It found that Mounjaro 15 mg produced 20.2% average weight loss compared with 13.7% for Wegovy 2.4 mg over 72 weeks. Around 45% of Mounjaro participants lost at least 25% of their body weight, compared with 19% on Wegovy.
However, Novo Nordisk's newer 7.2 mg dose of Wegovy (approved by the MHRA in January 2026) narrows the gap considerably. In the STEP UP trial, Wegovy 7.2 mg produced 20.7% average weight loss over 72 weeks, putting it roughly in line with Mounjaro 15 mg. This higher dose is now available in the UK through private prescription.
Important caveat: Trial populations differed, so these numbers are not perfectly comparable. The SURMOUNT-5 head-to-head trial is the most reliable comparison, but it used the older 2.4 mg Wegovy dose, not the newer 7.2 mg dose.
What are the side effects of each?
Both Wegovy and Mounjaro share a very similar side-effect profile because they both act on GLP-1 receptors. Most side effects are gastrointestinal and tend to be worst during the dose-escalation phase.
Common side effects (both drugs):
- Nausea: The most frequently reported side effect. Usually improves as your body adjusts over the first 4 to 8 weeks at each dose level.
- Vomiting and diarrhoea: Common in the first few weeks of treatment or after dose increases.
- Constipation: Affects roughly 1 in 4 users of either drug.
- Reduced appetite: This is both a therapeutic effect and a side effect. It is the main mechanism behind weight loss.
- Injection site reactions: Minor redness, itching, or bruising at the injection site.
- Hair thinning: Related to rapid weight loss rather than the drug itself. Usually temporary.
Serious side effects (rare, both drugs):
- Pancreatitis: Uncommon but requires immediate medical attention. Stop the medication and seek help if you experience severe, persistent abdominal pain.
- Gallbladder problems: Rapid weight loss increases the risk of gallstones.
- Kidney problems: Usually linked to dehydration from nausea and vomiting. Stay well hydrated.
- Thyroid tumour risk: Both carry a precaution for people with a personal or family history of medullary thyroid cancer or MEN2 syndrome.
Mounjaro-specific considerations:
- Oral contraceptive interaction: The MHRA advises that Mounjaro may reduce the effectiveness of the oral contraceptive pill. Barrier methods, patches, or hormonal coils may be more reliable alternatives during treatment.
- Euglycaemic ketoacidosis: A rare but potentially serious condition that can occur in non-diabetic patients experiencing severe gastrointestinal side effects. Wegovy is not associated with this risk.
In clinical trials, Mounjaro had a slightly lower discontinuation rate than Wegovy, suggesting that side effects may be marginally more tolerable for some patients.
What are the dosage schedules?
Both medications start at a low dose and increase gradually over several weeks to reduce side effects.
| Wegovy (semaglutide) | Mounjaro (tirzepatide) | |
|---|---|---|
| Starting dose | 0.25 mg | 2.5 mg |
| Dose steps | 0.25, 0.5, 1.0, 1.7, 2.4 mg (+ 7.2 mg) | 2.5, 5, 7.5, 10, 12.5, 15 mg |
| Standard max dose | 2.4 mg | 15 mg |
| Higher dose available | 7.2 mg (MHRA approved Jan 2026) | No |
| Time to maintenance dose | About 17 weeks | About 20 to 24 weeks |
| Injection frequency | Once weekly | Once weekly |
| Pen type | Single-dose FlexTouch pen | KwikPen (4 doses per pen) |
Dose increases happen every 4 weeks with both drugs. Your prescriber may slow the titration if you experience significant side effects at any step. Not everyone needs to reach the maximum dose. Some patients achieve sufficient weight loss at lower maintenance doses.
How much do they cost in the UK?
Following Eli Lilly's price increase in September 2025, Wegovy is generally the more affordable option at most dose levels for private patients.
| Dose level | Wegovy (per 4-week supply) | Mounjaro (per 4-week supply) |
|---|---|---|
| Starting dose | 0.25 mg: ~£89 | 2.5 mg: ~£149 |
| Mid-range | 1.0 mg: ~£139 | 7.5 mg: ~£249 |
| Standard maintenance | 2.4 mg: ~£189 | 15 mg: ~£299 |
| Higher dose | 7.2 mg: ~£259 | N/A |
At maintenance doses, the annual difference is roughly £600 to £1,100 in favour of Wegovy. Prices vary between pharmacies and online prescribing services, so it is worth comparing several providers. Both medications require an ongoing private prescription and clinical review, which may add £20 to £50 per consultation depending on the provider.
On the NHS, both drugs cost the standard prescription charge of £9.90 per item (free in Scotland, Wales, and Northern Ireland), but availability is extremely limited.
Can you get them on the NHS?
Both Wegovy and Mounjaro have been approved by NICE for NHS use, but access remains limited and subject to strict eligibility criteria.
Wegovy on the NHS (NICE TA875):
- Eligibility: BMI of 35 or above, or 30 or above with at least one weight-related health condition (type 2 diabetes, hypertension, sleep apnoea, etc.)
- Access route: Specialist NHS weight management services (Tier 3 or Tier 4)
- Maximum treatment duration: 2 years
- Waiting times: 6 months to 2 years depending on your local area
Mounjaro on the NHS (NICE TA1026):
- Eligibility: BMI of 40 or above with at least 4 weight-related conditions (stricter criteria than Wegovy)
- Access route: Through Integrated Care Boards, with a phased national rollout
- Broader commissioning: Expected from mid-2026 onwards
- Current reality: Most patients access Mounjaro privately
In practice, the majority of people using either drug in the UK access them through private prescriptions. Both require a clinical assessment before prescribing, regardless of whether you go NHS or private.
General eligibility (private, both drugs): Adults aged 18 or over with a BMI of 30 or above, or 27 or above with at least one weight-related health condition.
Which has better heart health evidence?
Wegovy currently has the stronger cardiovascular evidence.
The SELECT trial (over 17,000 participants) found that Wegovy reduced the risk of major adverse cardiovascular events (heart attack, stroke, or cardiovascular death) by 20% compared with placebo in adults with obesity and existing cardiovascular disease. This led to Wegovy receiving a specific cardiovascular risk reduction indication.
Mounjaro's cardiovascular data is still emerging. The SURPASS-CVOT trial showed Mounjaro was non-inferior to dulaglutide in adults with type 2 diabetes, with an 8% lower rate of cardiovascular events, but superiority was not established. A dedicated cardiovascular outcomes trial in weight management (SURMOUNT-MMO) is still ongoing.
If you have existing cardiovascular disease or significant cardiovascular risk factors, Wegovy's proven heart protection may be a strong reason to choose it over Mounjaro, especially if cost is also a factor.
How to decide which is right for you
There is no single "best" choice. The right medication depends on your priorities, budget, and medical history.
Mounjaro may suit you better if:
- You want the maximum possible weight loss at standard doses
- You have tried a GLP-1 agonist before (such as Ozempic or Saxenda) and the results were insufficient
- You value having more dose flexibility (six dose steps vs five)
- Cost is not your primary concern
Wegovy may suit you better if:
- You want a more affordable treatment at maintenance doses
- You have existing cardiovascular disease or significant heart risk factors (stronger evidence from the SELECT trial)
- You prefer a well-established GLP-1 treatment with a longer UK track record
- You are eligible for the newer 7.2 mg dose, which narrows the weight-loss gap with Mounjaro
- You want easier NHS access (broader NICE criteria)
Neither medication is suitable during pregnancy or breastfeeding. Both should be discontinued at least 2 months before a planned pregnancy. Always discuss your full medical history with a prescriber before starting either treatment.
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Frequently asked questions
Can you switch from Wegovy to Mounjaro or vice versa?
Yes, switching is possible under medical supervision. Your prescriber will typically restart you at a lower dose of the new medication and titrate upwards, rather than jumping straight to a high dose. Common reasons for switching include insufficient weight loss, intolerable side effects, or cost considerations. Always discuss the switch with your prescriber rather than stopping one and starting the other independently.
Is Mounjaro better than Wegovy for type 2 diabetes?
Both medications improve blood sugar control, but they work through slightly different pathways. Mounjaro's dual GIP/GLP-1 action may offer additional benefits for blood sugar management. However, for diabetes specifically, Ozempic (the diabetes-licensed version of semaglutide) and Mounjaro's diabetes indication (Zepbound is the weight-loss brand in the US; in the UK, Mounjaro covers both) are the primary options. Your diabetologist or GP is best placed to advise on which suits your diabetes management plan.
Do you regain weight after stopping Wegovy or Mounjaro?
Clinical evidence suggests that most people regain a significant portion of lost weight after stopping either medication if they do not maintain lifestyle changes. The STEP 1 extension trial found that participants regained about two-thirds of their lost weight within one year of stopping semaglutide. This is not a failure of the drugs; it reflects the fact that obesity has biological drivers (altered hunger hormones, metabolic adaptation) that reassert themselves when treatment stops. Long-term or indefinite use may be necessary for sustained results.
Can you take Wegovy or Mounjaro with other medications?
Both drugs can interact with certain medications. Mounjaro in particular may reduce the absorption of oral contraceptives and other medications taken by mouth, because it slows gastric emptying. If you take time-sensitive oral medications (such as the contraceptive pill, thyroid medication, or certain antibiotics), discuss timing adjustments with your prescriber. Neither drug should be combined with other GLP-1 agonists.
Is there an oral version of either drug?
An oral version of semaglutide (the active ingredient in Wegovy) has been developed, with doses from 1.5 mg to 25 mg taken once daily. It offers a needle-free alternative for people who dislike injections. There is no oral version of tirzepatide (Mounjaro) currently available in the UK. Speak with your prescriber if you are interested in the oral semaglutide option.
Are compounded or "generic" versions safe?
The MHRA has warned against purchasing compounded, unregulated, or counterfeit versions of semaglutide or tirzepatide. These products may contain incorrect doses, contaminants, or no active ingredient at all. Always obtain your medication through a GPhC-registered pharmacy with a valid prescription from a registered prescriber. If a deal looks too good to be true, it almost certainly is.
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