Choosing Between Mounjaro, Wegovy and Saxenda: What UK Patients Need to Know Before Prescribing Begins

Prescription weight-loss injections have moved from specialist clinics into mainstream British healthcare, but the choice between them is rarely explained clearly. Patients referred by their GP or assessed by a private provider are often presented with a decision — Mounjaro, Wegovy or Saxenda — without a straightforward explanation of what separates them. This article sets out the differences in plain terms, so that any conversation with a prescriber starts from an informed position.

Three Medications, Three Profiles

All three medicines work on the appetite-regulation system, but they are not identical.

Wegovy (semaglutide) is a once-weekly injection that mimics GLP-1, a gut hormone that slows digestion and signals fullness to the brain. Licensed in the UK for weight management, it is typically introduced at a low dose and increased gradually over around four months.

Mounjaro (tirzepatide) goes a step further, targeting both GLP-1 and a second hormone pathway called GIP. This dual action appears to produce somewhat larger average weight reductions in clinical trials, and it is also administered weekly. It was approved for weight management in the UK in late 2024.

Saxenda (liraglutide) is the oldest of the three and works on GLP-1 alone, but because it clears the body quickly it must be injected daily. It is generally positioned as an option where once-weekly treatment is unsuitable or has proven ineffective.

What the Evidence Suggests

Trial data gives a broad indication of what patients might expect, though individual results vary considerably.

• Mounjaro has shown average weight losses in the region of 15–20% of body weight over 72 weeks in studies at higher doses.
• Wegovy trials reported averages around 15% over a similar period.
• Saxenda typically produces more modest results, with averages closer to 5–8%.

These figures come from controlled research settings. Real-world outcomes depend heavily on dose tolerance, adherence and the lifestyle support provided alongside treatment.

Side Effects: What Prescribers Will Discuss

The side-effect profiles overlap substantially, since all three act on the digestive system. Nausea is the most frequently reported issue, particularly during dose escalation. Vomiting, constipation, diarrhoea and indigestion are also common in the early weeks.

Saxenda's daily injections can intensify side effects for some patients, as each dose re-triggers the adjustment period. Weekly medications smooth this out, though the escalation schedule still matters. Rarer but more serious risks — including gallbladder problems and, for patients with certain family histories, thyroid concerns — should form part of any prescriber consultation.

Availability and Cost in the UK

Access differs sharply between the NHS and private routes.

On the NHS, Wegovy is available through specialist weight-management services under NICE guidance, with strict eligibility criteria — typically a BMI of 35 or over (or 30 in some cases), plus at least one weight-related condition. Mounjaro is being rolled out incrementally within NHS pathways. Saxenda's NHS use is more restricted.

Privately, all three can be prescribed following an online or in-clinic assessment. Indicative monthly costs currently sit at roughly:

• Saxenda: £150–£250, depending on dose
• Wegovy: £200–£300, varying by pen strength
• Mounjaro: £150–£300, with lower doses cheaper

Prices move frequently, and reputable providers publish current rates openly. Patients should be wary of offers that seem implausibly cheap, as previous shortages led to a grey market in counterfeit pens.

Matching the Medication to the Patient

There is no single best option. A patient who struggles with daily routines may find weekly injections far more sustainable. Someone with type 2 diabetes may be directed towards Mounjaro for its additional metabolic effects. Those who cannot tolerate higher-potency medicines may do better on Saxenda's gentler, titratable approach.

Eligibility, medical history and personal preference should all shape the decision — which is precisely why a proper consultation, rather than a simple online purchase, remains the correct starting point for any of these treatments.