Ozempic vs Mounjaro: Which is More Effective for Weight Loss?

16 / Jun

If you’re researching weight loss injections in the UK, you’ve likely come across two major names: Ozempic and Mounjaro. Both medications were originally developed to treat type 2 diabetes but have gained massive popularity for their weight loss benefits — especially through private prescriptions.

But which one is more effective? And how do they compare in terms of results, side effects, and availability in the UK?
This guide will break it all down for you — using the latest scientific evidence — to help you make an informed decision.

Understanding the Active Ingredients

Ozempic contains semaglutide, a glucagon-like peptide-1 (GLP-1) receptor agonist. Originally synthesized for the management of type 2 diabetes, semaglutide’s mechanism of action involves mimicking the body’s natural GLP-1 hormone. When administered, semaglutide binds to GLP-1 receptors found in various tissues, including the brain, pancreas, and gastrointestinal tract. This binding stimulates glucose-dependent insulin secretion from the pancreatic beta cells, thereby helping to lower blood sugar levels. Crucially for weight management, semaglutide also acts on GLP-1 receptors in the brain’s appetite regulation centers, promoting a feeling of satiety and reducing hunger. Furthermore, it slows gastric emptying, which means food stays in the stomach longer, contributing to prolonged fullness and reduced food intake. These combined effects on appetite suppression and delayed digestion lead to a sustained reduction in calorie consumption and, consequently, weight loss.

Mounjaro, on the other hand, contains tirzepatide, a novel dual-action medication that uniquely targets both GLP-1 and glucose-dependent insulinotropic polypeptide (GIP) receptors. While GLP-1’s role in appetite and glucose regulation is well-established, GIP is another incretin hormone that also plays a significant role in metabolic control. By activating both these receptor pathways, tirzepatide leverages a synergistic effect. GIP receptors are abundant in fat cells and contribute to energy balance and fat metabolism. The dual agonism of tirzepatide leads to enhanced insulin secretion, improved insulin sensitivity, and a more pronounced impact on satiety and gastric emptying compared to medications that only target GLP-1. This broader influence on metabolic pathways is believed to be the underlying reason for its potentially greater efficacy in both glycemic control and significant weight reduction.

Weight Loss Effectiveness: The Evidence

Ozempic Weight Loss Results

Clinical studies demonstrate that Ozempic produces substantial weight loss outcomes. In real-world cohort studies, patients achieved average weight loss of 5.9% at 3 months and 10.9% at 6 months. Long-term studies show even more impressive results, with participants losing an average of 15.2% of their body weight over 104 weeks compared to 2.6% with placebo.

The SUSTAIN trials found that patients on Ozempic 1mg lost an average of 4.9kg, with up to 66% of participants achieving more than 5% body weight reduction. In cardiovascular outcome studies, participants maintained an average 10.2% weight loss over 4 years.

Mounjaro Superior Performance

Mounjaro has demonstrated superior effectiveness compared to Ozempic in head-to-head comparisons. Clinical trials show that 42.3% of people taking tirzepatide achieved at least 15% body weight loss within one year, compared to only 19.3% taking semaglutide.

The SURMOUNT trials revealed remarkable results, with participants achieving up to 21% average weight loss at higher doses. In the SURMOUNT-3 study, participants achieved a total mean weight loss of 26.6% from study entry over 84 weeks when combining tirzepatide with intensive lifestyle intervention.

Weight Loss: Dosing and Administration

Medication	Starting Dose	Dose Escalation	Maximum Dose	Dose Interval
Ozempic	0.25 mg weekly (4 weeks)	Increases to 0.5 mg weekly, then 1 mg or 2 mg as needed	2 mg weekly	Every 4 weeks (as needed)
Mounjaro	2.5 mg weekly (4 weeks)	Progresses to 5 mg, 7.5 mg, 10 mg, 12.5 mg, 15 mg weekly	15 mg weekly	Every 4 weeks (minimum)

Side Effects and Safety Profile

Like all medications, Ozempic and Mounjaro come with potential side effects, primarily related to their impact on the gastrointestinal system. Understanding these common adverse events is crucial for patients embarking on treatment.

Ozempic commonly elicits gastrointestinal disturbances. These include nausea, a frequently reported symptom, along with changes in bowel habits such as diarrhoea and constipation. Patients may also experience mild localised reactions at the injection site, typically involving redness, itching, or swelling. It’s important to note that for most individuals, these side effects are mild to moderate in severity and tend to be most pronounced when initiating treatment or increasing the dose.

As the body gradually adapts to the medication, these symptoms often diminish over time. Healthcare providers typically recommend a slow titration schedule to help mitigate these initial discomforts, allowing the body to adjust more smoothly. Strategies like eating smaller, more frequent meals, avoiding fatty foods, and staying well-hydrated can also help manage these symptoms.

Mounjaro exhibits a side effect profile that largely mirrors that of GLP-1 receptor agonists, with gastrointestinal issues being most prominent. Nausea is the most frequently reported adverse event, observed in a significant portion of patients, particularly during the initial lead-in treatment phase (e.g., 35.5% in some studies). Other common gastrointestinal effects include diarrhoea (e.g., 21.1%), constipation (e.g., 20.7%), and vomiting (e.g., 16.3%). Beyond digestive issues, some patients taking Mounjaro have reported additional, though less frequent, side effects such as dizziness, headache, hair loss, and fatigue.

The severity and incidence of gastrointestinal side effects with Mounjaro appear to be dose-dependent, with meta-analysis data indicating that higher doses, particularly the 15mg weekly dose, are associated with an increased risk for these adverse events compared to lower doses. This underscores the importance of gradual dose escalation under medical supervision to optimise tolerance. While generally well-tolerated, patients should discuss any persistent or severe side effects with their healthcare provider

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Availability and Cost Considerations

NHS Availability

Mounjaro has received NICE approval for NHS provision, but availability is strictly limited. Initially, only 250,000 people with the highest clinical need will receive access over three years, primarily those with BMI over 35 and weight-related comorbidities.

Ozempic availability on the NHS remains primarily for diabetes management, though some off-label prescribing occurs.

Private Costs

UK private prescription costs vary but typically range from £150-300 monthly depending on dose and provider. Check out our Mounjaro page for Pharmacy Advance pricing

Weight Loss Clinical Recommendations

Healthcare providers should consider several factors when choosing between these medications:

Choose Mounjaro when:

Maximum weight loss is the primary goal
Patient can tolerate potentially higher rates of gastrointestinal side effects
Cost is not a primary limiting factor

Choose Ozempic when:

Patient has established cardiovascular disease (additional cardiac benefits)
Lower starting side effect profile is preferred
Diabetes management is also required

Conclusion

While both Ozempic and Mounjaro offer significant benefits, current evidence suggests Mounjaro (tirzepatide) provides superior effectiveness. The dual-receptor mechanism of tirzepatide consistently demonstrates higher rates of clinically meaningful weight loss across multiple studies.

However, the choice between these medications should always involve comprehensive medical evaluation considering individual health status, comorbidities, side effect tolerance, and access considerations. Both medications represent important advances in obesity treatment, offering hope for sustainable long-term weight management when combined with lifestyle modifications.

View Weight Loss Treatment

Sources

Outcomes Associated With Semaglutide Treatment: View here
Long-term effects of semaglutide in obesity without diabetes: View here
Early cardiovascular benefits of semaglutide seen within months in SELECT trial: View here
Continued Tirzepatide Treatment for Weight Maintenance: View here
UK Parliament Research Briefing on Tirzepatide Rollout: View here
Research on Tirzepatide’s Weight Loss Efficacy: View here
Official MHRA Authorization for Mounjaro (Tirzepatide) for Weight Management: View here
Tirzepatide vs. Semaglutide Drug Information Comparison: View here
Official Mounjaro (Tirzepatide) Manufacturer’s Information on Side Effects and Usage: View here
Drug Information Resource Detailing How Ozempic (Semaglutide) Works: View here
Official European Medicines Agency (EMA) Product Information for Ozempic: View here
Ozempic Dosage, Forms, and Strengths: View here
Drug Information Comparison of Various Weight Loss Medications (Ozempic, Mounjaro, Wegovy, Zepbound): View here