Wegovy and Mounjaro are prescription weight loss injections available in the UK. Wegovy contains semaglutide and targets one hormone receptor. Mounjaro contains tirzepatide and targets two.
Clinical trials show Mounjaro tends to produce greater weight loss on average. But neither is universally “better.” The right choice depends on your health history, how your body responds, and what your prescriber recommends.
We have made a full breakdown so you can go into your consultation better prepared.
What Is Wegovy and How Does It Work?
Wegovy is a prescription weight loss injection containing semaglutide. It belongs to a class of medicines called GLP-1 receptor agonists.
GLP-1 is a hormone your gut releases after eating. It tells your brain you are full, slows digestion, and reduces appetite. Semaglutide mimics this hormone. It keeps you feeling fuller for longer, which helps reduce how much you eat.
Wegovy was approved by the MHRA for weight management in adults with a BMI of 30 or above. It can also be prescribed for those with a BMI of 27 or above if they have a weight-related health condition such as type 2 diabetes or high blood pressure. It is injected once a week using a pre-filled pen.
Wegovy Dosages
Wegovy is started at a low dose, and then dose is increased gradually over months. This approach reduces the risk of side effects like nausea.
| Week | Dose |
| Weeks 1–4 | 0.25 mg once weekly |
| Weeks 5–8 | 0.5 mg once weekly |
| Weeks 9–12 | 1 mg once weekly |
| Weeks 13–16 | 1.7 mg once weekly |
| Week 17 onwards | 2.4 mg once weekly (maintenance dose) |
Some patients stay on a lower dose if they cannot tolerate the full 2.4 mg. Your prescriber will guide this.
What Is Mounjaro and How Does It Work?
Mounjaro is a prescription injection containing tirzepatide. It works differently to Wegovy because it targets two hormone receptors, not one.
Tirzepatide activates both GLP-1 and GIP receptors. GIP is another gut hormone that plays a role in insulin release and fat storage. By targeting both pathways at once, Mounjaro has a stronger combined effect on appetite and blood sugar regulation.
In the UK, Mounjaro is licensed for weight management in adults with a BMI of 30 or above. Like Wegovy, it can be prescribed for those with a BMI of 27 or above if they have an obesity-related condition. It is also a once-weekly injection.
Mounjaro Dosages
Mounjaro follows a similar step-up schedule over several months.
| Week | Dose |
| Weeks 1–4 | 2.5 mg once weekly |
| Weeks 5–8 | 5 mg once weekly |
| Weeks 9–12 | 7.5 mg once weekly |
| Weeks 13–16 | 10 mg once weekly |
| Weeks 17–20 | 12.5 mg once weekly |
| Week 21 onwards | 15 mg once weekly (maintenance dose) |
Not everyone reaches the 15 mg dose. Many people achieve good results at 10 or 12.5 mg.
Key Differences Between Wegovy and Mounjaro
| Feature | Wegovy | Mounjaro |
| Active ingredient | Semaglutide | Tirzepatide |
| Mechanism | GLP-1 receptor agonist | Dual GLP-1 and GIP receptor agonist |
| Maximum dose | 2.4 mg | 15 mg |
| Injection frequency | Once weekly | Once weekly |
| Approved for type 2 diabetes | No (separate product, Ozempic) | Yes (also approved as Mounjaro for T2D) |
| NHS availability | Available via specialist services | Available via specialist services |
| Average weight loss | Around 15% body weight | Around 20–22% body weight |
The most important structural difference is the dual-action mechanism in Mounjaro. This is why it tends to produce greater weight loss in clinical trials.
Effectiveness: Which Drug Leads to More Weight Loss?
The SURMOUNT-1 trial found that adults taking tirzepatide at the highest dose lost an average of 22.5% of their body weight over 72 weeks. That is significant for any weight loss treatment.
The STEP 1 trial for semaglutide showed an average weight loss of around 14.9% over 68 weeks.
A head-to-head comparison published in the Journal of the American Medical Association (2023) found tirzepatide was associated with greater weight loss than semaglutide across all dose comparisons.
Individual results vary. Some people respond very well to Wegovy. Others plateau on Mounjaro. Genetics, diet, activity levels, and other health conditions all play a part. Weight loss medication is not a guaranteed outcome. It works best alongside dietary changes and regular movement.
Side Effects and Safety Considerations
Both medications share a similar side effect profile because they both activate GLP-1 receptors. The most common issues are gastrointestinal.
Common side effects for both:
- Nausea (especially in the first few weeks)
- Vomiting
- Diarrhoea or constipation
- Stomach discomfort or bloating
- Reduced appetite (this is partly the intended effect)
Most of these settle down as your body adjusts. They tend to be worse when the dose is increased, which is why the step-up schedule exists.
Less common but serious concerns to be aware of:
- Pancreatitis (inflammation of the pancreas) – rare but reported with both drugs
- Gallbladder problems, including gallstones
- Increased heart rate
- Potential thyroid effects – both drugs carry a warning regarding thyroid tumours based on animal studies, though this has not been confirmed in humans
Neither medication is suitable if you have a personal or family history of medullary thyroid carcinoma or Multiple Endocrine Neoplasia syndrome type 2 (MEN2).
Mounjaro is not recommended in pregnancy. Neither drug should be used by people with type 1 diabetes or those with a history of severe gastrointestinal conditions such as gastroparesis.
Note: Always disclose your full medical history to your prescriber before starting either treatment.
Wegovy vs Mounjaro Cost Comparison
Cost is a real-world factor that shapes treatment decisions. Both are available privately in the UK, and neither is routinely available on the NHS for general weight management.
| Medication | Approximate Monthly Cost (UK, Private) |
| Wegovy (2.4 mg maintenance) | £200–£280 per month |
| Mounjaro (15 mg maintenance) | £175–£250 per month |
Prices vary depending on the pharmacy and prescriber. Starter doses tend to cost less because the dose is lower.
Mounjaro is often slightly cheaper per pen, which surprises people given that it tends to produce better results. This can make it an attractive option for cost-conscious patients.
Neither drug is cheap for long-term use. If budget is a concern, discuss this openly with your prescriber. Some clinics offer package deals that include consultations and monitoring.
How Do I Know Which One to Take?
This is not a decision to make based on a comparison article alone. You need a prescriber to assess your full medical history. Here are some general patterns that may guide the conversation:
Wegovy may be more suitable if:
- You have previously responded well to semaglutide (such as Ozempic for type 2 diabetes)
- Your prescriber has specific clinical reasons to prefer a single-agonist approach
- Mounjaro is unavailable or not appropriate for your specific health profile
Mounjaro may be more suitable if:
- You want the treatment with the strongest evidence for weight loss
- You have type 2 diabetes and want a drug licensed for both weight and blood sugar management
- Previous weight loss treatments have not worked well enough
If you have tried one and it has not delivered results after several months at the maintenance dose, it is reasonable to ask your prescriber whether switching makes sense. The most important thing is to take the medication consistently, follow the dietary guidance given, and attend your follow-up appointments.
FAQs
Can I switch from Wegovy to Mounjaro if it stops working?
Yes, this is possible. If you have been on Wegovy at the maintenance dose for several months and have not seen adequate results, your prescriber may consider switching to Mounjaro. Never switch medications without guidance from your prescriber.
Do Wegovy and Mounjaro interact with other medications?
Both can affect the absorption of oral medications because they slow gastric emptying. This is relevant for oral contraceptives, thyroid medications, and blood pressure tablets. Always give your prescriber and pharmacist a full list of what you are currently taking.
Will I regain weight if I stop taking Wegovy or Mounjaro?
Most clinical evidence suggests that weight regain is common after stopping these medications, unless lifestyle changes have been firmly established. These drugs suppress appetite while you are taking them. Once you stop, appetite and food intake can return to previous levels. Long-term or indefinite use may be needed for sustained results in some patients.
Are these treatments suitable for older adults or people with heart disease?
Wegovy has cardiovascular outcome data from the SELECT trial showing a reduction in major cardiovascular events in people with pre-existing heart disease. Older adults can be prescribed either medication, but the decision requires careful assessment of kidney function, other medications, and overall frailty. Speak to your prescriber about your full profile.
How long does it take to see results on either medication?
Most people start noticing reduced appetite within the first few weeks. Visible weight loss typically becomes more obvious from weeks 8 to 12 onwards, as the dose increases. The most significant weight loss usually occurs between months 3 and 12. Both drugs require patience and consistency. Neither will produce dramatic overnight results.
Conclusion
Both Wegovy and Mounjaro are effective, clinically backed weight loss treatments. Mounjaro, with its dual-receptor mechanism, tends to produce greater average weight loss based on current trial data. Wegovy has a longer track record and strong cardiovascular safety data.
The best treatment is the one that suits your health profile, fits your budget, and that you can maintain safely over time.
Ready to take the next step? Contact us today to book your weight loss consultation.
