Wegovy vs Mounjaro: An Honest Comparison of the UK’s Leading Weight Loss Injections

If you are researching prescription weight-loss treatments in the UK, you have almost certainly come across two names: Wegovy and Mounjaro. Both are once-weekly injectable medications that have generated enormous interest, significant clinical trial data, and understandable confusion for patients trying to work out which one might be right for them.

This article sets out the key differences and similarities clearly, drawing on clinical evidence rather than marketing claims. Neither medication is universally “better” than the other. The right choice depends on your medical history, your body, your goals, and what your prescriber recommends. Our aim is to give you enough information to have a more informed conversation with them.

The Basics: What Are Wegovy and Mounjaro?

Both Wegovy and Mounjaro are prescription-only medications licensed in the UK for weight management in adults who meet specific clinical criteria. According to the NHS, approximately 1 in 4 adults in the UK lives with obesity, and these medications represent a relatively new class of treatment that has shown results far exceeding anything previously available.

Wegovy (Semaglutide)

Wegovy contains the active ingredient semaglutide. It is manufactured by Novo Nordisk and was originally developed from the same compound used in Ozempic (a diabetes medication). Wegovy is specifically licensed for weight management and is administered as a once-weekly subcutaneous injection.

How it works: Semaglutide is a GLP-1 receptor agonist. It mimics the naturally occurring gut hormone GLP-1, which plays a key role in appetite regulation. When you eat, GLP-1 signals your brain that you are full, slows down the rate at which food empties from your stomach, and helps stabilise blood sugar levels. Wegovy amplifies these effects, reducing hunger and helping you eat less without relying solely on willpower.

Mounjaro (Tirzepatide)

Mounjaro contains the active ingredient tirzepatide. It is manufactured by Eli Lilly and represents a newer approach to weight management. It is also administered as a once-weekly subcutaneous injection.

How it works: Tirzepatide is a dual GIP and GLP-1 receptor agonist. In addition to the GLP-1 effects described above, it also activates GIP (glucose-dependent insulinotropic polypeptide) receptors. GIP is another gut hormone involved in appetite control, insulin secretion, and how the body metabolises fat. This dual action is thought to be responsible for Mounjaro’s stronger average weight-loss results compared to GLP-1-only medications.

Weight Loss Results: What the Clinical Trials Show

This is typically the first question people ask, and the clinical data is substantial for both medications.

Wegovy Clinical Data

The STEP clinical trial programme evaluated Wegovy across several large studies. Key findings include:

• Standard dose (2.4 mg): Participants lost an average of approximately 15% of their body weight over 68 weeks.
• Higher dose (7.2 mg): The newer, higher dose achieved approximately 20.7% body weight loss in clinical trials, with nearly half of participants losing 20% or more.

For someone starting at 100 kg, the standard Wegovy dose translated to an average loss of roughly 15 kg, while the higher dose achieved approximately 20.7 kg over the trial period.

Mounjaro Clinical Data

The SURMOUNT-1 trial, published in the New England Journal of Medicine, evaluated Mounjaro across three dose levels over 72 weeks:

• 5 mg dose: approximately 16% body weight loss
• 10 mg dose: approximately 21.4% body weight loss
• 15 mg dose: approximately 22.5% body weight loss

For a 100 kg starting weight, the highest dose group lost an average of around 22.5 kg.

How to Interpret These Numbers

On paper, Mounjaro at its highest dose produced slightly greater average weight loss than Wegovy at its standard dose. However, the newer Wegovy 7.2 mg dose narrows this gap considerably. Direct head-to-head trials comparing the two medications at their optimal doses are still emerging, and averages do not tell you what your result will be.

Individual responses vary widely within both trial groups. Some participants on Wegovy lost more than some participants on Mounjaro, and vice versa. The medication that works best for you depends on factors beyond what any average can capture.

Eligibility: Who Can Take Each Medication?

The eligibility criteria for both medications are broadly similar in the UK:

• BMI of 30 or higher (classified as obesity), or
• BMI of 27 or higher with at least one weight-related health condition, such as type 2 diabetes, high blood pressure, high cholesterol, or obstructive sleep apnoea.

Your prescriber will also consider your medical history, current medications, and individual circumstances when recommending one medication over the other.

Who Might Be Better Suited to Wegovy?

• Patients starting prescription weight-loss treatment for the first time, as Wegovy has a longer track record in the UK.
• Those with cardiovascular concerns. The SELECT trial demonstrated that semaglutide reduced the risk of major cardiovascular events (heart attack, stroke) by 20%, even in patients with minimal weight loss. This cardiovascular benefit is one of Wegovy’s distinctive advantages.
• Patients who prefer a medication with a well-established safety profile over a longer period.

Who Might Be Better Suited to Mounjaro?

• Patients who have tried a GLP-1-only medication (like Wegovy or Saxenda) and found the results insufficient.
• Those with significant insulin resistance or type 2 diabetes, as the dual GIP/GLP-1 mechanism may offer additional metabolic benefits.
• Patients who need more substantial weight loss and are willing to explore a newer treatment option.

Side Effects: What to Expect

Both medications share a similar side-effect profile, largely because they both act on the GLP-1 pathway. The most common side effects are gastrointestinal and tend to be most pronounced during the early weeks of treatment and following each dose increase.

Common Side Effects (Both Medications)

• Nausea (the most frequently reported side effect for both)
• Diarrhoea
• Constipation
• Vomiting
• Bloating and indigestion
• Headache
• Fatigue
• Sulphur burps (more commonly associated with semaglutide, though reported with both)

For most patients, these side effects are mild to moderate and diminish as the body adjusts to the medication. Eating smaller meals, avoiding very fatty foods, staying well hydrated, and increasing fibre gradually can all help manage symptoms.

Rare but Serious Risks (Both Medications)

• Pancreatitis: Severe abdominal pain radiating to the back. Seek emergency medical attention if this occurs.
• Gallbladder problems: Including gallstones, which may be more common during rapid weight loss.
• Serious allergic reactions: Swelling of the face, lips, tongue, or throat; difficulty breathing.
• Thyroid concerns: Both carry warnings about medullary thyroid carcinoma in animal studies, though this has not been confirmed in humans. Both are contraindicated in patients with a personal or family history of medullary thyroid carcinoma or multiple endocrine neoplasia syndrome type 2 (MEN 2).

Contraindications: Who Should Not Take These Medications

Neither Wegovy nor Mounjaro is suitable for everyone. Both are contraindicated in:

• People with a personal or family history of medullary thyroid carcinoma
• People with multiple endocrine neoplasia syndrome type 2 (MEN 2)
• Those with a history of pancreatitis
• Pregnant women or those planning to become pregnant
• People with type 1 diabetes
• Those with severe gastrointestinal conditions (such as gastroparesis)
• Patients with a history of severe kidney disease

This is not an exhaustive list. Your prescriber will conduct a thorough medical assessment before recommending either medication.

Dosing and Titration

Both medications follow a gradual dose-escalation schedule to minimise side effects.

Wegovy Dosing Schedule

• Month 1: 0.25 mg weekly
• Month 2: 0.5 mg weekly
• Month 3: 1 mg weekly
• Month 4: 1.7 mg weekly
• Month 5 onwards: 2.4 mg weekly (maintenance dose)
• Higher dose option: 7.2 mg for patients already stable on 2.4 mg who may benefit from further weight loss

Mounjaro Dosing Schedule

• Weeks 1-4: 2.5 mg weekly
• Weeks 5-8: 5 mg weekly
• Subsequent increases: 7.5 mg, 10 mg, 12.5 mg, or 15 mg, based on clinical response and tolerability

Your prescriber will determine the most appropriate maintenance dose based on your individual response, side-effect tolerance, and treatment goals.

Cost Comparison in the UK

As both medications are available primarily through private prescriptions for weight management (NHS availability is limited and varies by region), cost is a practical consideration for many patients across England, Scotland, Wales, and Northern Ireland.

• Wegovy: Starting from approximately 130 pounds per month for the lowest dose, increasing with dose escalation.
• Mounjaro: Starting from approximately 140 pounds per month for the 2.5 mg dose, also increasing with dose escalation. Note that Mounjaro experienced a price increase in September 2025, which has affected costs across all UK providers.

Prices vary between providers and may change. It is worth comparing several regulated providers and asking about any ongoing subscription or treatment programme costs.

Other Weight Loss Medications: How Do They Compare?

Wegovy and Mounjaro are not the only options available. Two other medications are sometimes considered:

Saxenda (Liraglutide)

Saxenda is an older GLP-1 receptor agonist that requires daily injections rather than weekly. Clinical trials showed average weight loss of approximately 8% to 10% of body weight, which is less than both Wegovy and Mounjaro. It may be appropriate for patients who do not tolerate the newer medications or who prefer to start with a less potent option.

Orlistat

Orlistat is an oral medication (tablet) that works by blocking the absorption of approximately 25% of dietary fat. It produces more modest weight loss (typically 5% to 10%) and requires a low-fat diet to avoid unpleasant gastrointestinal side effects. It remains available on the NHS and is significantly cheaper than injectable treatments.

Making the Decision: A Summary Comparison

The Bottom Line

Both Wegovy and Mounjaro are effective, evidence-based weight-loss medications that represent a genuine step forward in treating obesity. Neither is a magic solution; both work best when combined with sustainable dietary changes, regular physical activity, and ongoing medical supervision.

If you are trying to decide between them, the most important step is to speak with a qualified prescriber who can assess your individual situation. Factors like your medical history, previous treatment experiences, cardiovascular risk profile, and personal preferences all feed into the recommendation.

What matters most is not which medication you choose, but that you receive proper clinical support throughout your treatment journey.

Frequently Asked Questions

Can I switch from Wegovy to Mounjaro (or vice versa)?

Yes, switching between the two medications is possible with clinical supervision. Your prescriber will advise on the appropriate starting dose for the new medication based on your current dose and treatment history. A brief adjustment period is normal, and you may experience some side effects again as your body adapts to the different medication.

Are Wegovy and Mounjaro available on the NHS?

NHS availability for weight management varies significantly across the UK and is typically limited to specialist weight-management services. NICE has approved tirzepatide for use in certain NHS pathways, and semaglutide has similar approvals. However, waiting lists for NHS weight-management services can be lengthy. Many patients choose to access these medications through regulated private providers for faster access.

Which medication has fewer side effects?

Both medications share a very similar side-effect profile, dominated by gastrointestinal symptoms (nausea, diarrhoea, constipation). Neither has been shown to be consistently better tolerated than the other across clinical trials. Some individuals tolerate one better than the other, which is one reason prescribers may suggest switching if side effects are problematic.

Will I regain weight if I stop taking either medication?

Clinical evidence shows that weight regain is common after stopping either medication. This is not a failure of the treatment; it reflects the chronic nature of obesity as a medical condition. Many patients continue treatment long-term with their prescriber’s guidance. Others use the medication period to establish sustainable lifestyle habits that help maintain some of the weight loss after stopping.

Can I take Wegovy or Mounjaro if I have type 2 diabetes?

Yes, both medications can be used in patients with type 2 diabetes, and both improve blood sugar control. However, if you are already taking diabetes medications (particularly insulin or sulphonylureas), your prescriber will need to adjust your diabetes treatment to avoid hypoglycaemia. Mounjaro is also separately licensed for the treatment of type 2 diabetes in the UK.