Mounjaro vs Wegovy: Which Weight Loss Injection Is Right for You?

Mounjaro and Wegovy are the two names that come up most often when people start researching weight loss injections, and for good reason. They are the most prescribed GLP-1 treatments in the UK, and both have significant clinical results behind them. But when two treatments are this closely associated in the public mind, choosing between them can feel genuinely overwhelming, particularly when so much of what you read online is either marketing or anecdote.

This article is a clinician-led comparison rather than a sales pitch for either option. It walks through how Mounjaro and Wegovy work, what results the evidence supports, how they are dosed, their side effects, who is eligible, and how cost compares, so you can understand the real differences. Neither medication is universally "better", and the most useful question is usually which one suits your individual circumstances.

How do Mounjaro and Wegovy work?

Both Mounjaro and Wegovy belong to a class of medicines that mimic gut hormones your body produces after eating, but they are not identical. Mounjaro (tirzepatide) is a dual agonist: it acts on two receptors, GLP-1 and GIP (glucose-dependent insulinotropic polypeptide). Wegovy (semaglutide) acts on the GLP-1 receptor alone. [1][2]

In practical terms, both work through the same core mechanisms. They reduce appetite by acting on areas of the brain involved in hunger, slow the rate at which the stomach empties so you feel fuller for longer, and help regulate blood sugar. [1][2] Mounjaro’s additional action on the GIP receptor is thought to enhance these effects, which may partly explain the differences seen in clinical trials. The key point is that both amplify signals your body already produces, rather than introducing something entirely foreign.

Mounjaro vs Wegovy: what results can you expect?

For much of the time these treatments have been available, comparisons relied on separate trials. In the SURMOUNT-1 trial, participants on the highest dose of tirzepatide lost an average of around 22.5% of their body weight over 72 weeks. [3] In the STEP 1 trial, participants on semaglutide 2.4 mg lost an average of around 14.9% over 68 weeks. [4]

The first head-to-head comparison, the SURMOUNT-5 trial, was published in 2025 and found that tirzepatide led to greater average weight loss than semaglutide 2.4 mg, at around 20.2% compared with 13.7% over 72 weeks. [5] More recently, the picture has shifted again: the MHRA has approved a higher 7.2 mg dose of Wegovy, which in trials helped more than one in five people achieve over 20% weight loss, narrowing the gap between the two treatments. [6]

It is important to read these figures for what they are: averages across large groups of people, not guarantees. Individual results vary considerably depending on starting weight, dose, diet, activity and individual physiology, and comparing your own progress to a trial average, or to before-and-after photos on social media, is not a reliable way to judge whether treatment is working. Realistic weight loss timelines tend to show gradual, steady progress building over several months rather than an overnight transformation, so patience with the process matters as much as the headline trial figures.

Dosing and administration: how do they differ?

Both Mounjaro and Wegovy are given as a once-weekly injection under the skin, using a pre-filled pen, and both are started at a low dose that is increased gradually over time. This step-up approach, known as titration, is designed to let the body adjust and to reduce the likelihood of side effects. [1][2]

Mounjaro is typically started at 2.5 mg once weekly and increased in steps if needed, with doses of 5 mg, 10 mg or 15 mg depending on response and tolerability. [1] Wegovy usually begins at 0.25 mg once weekly and is increased over around four months to a dose of 2.4 mg if needed, with the newer 7.2 mg dose now available as a higher-strength option for some patients. [2][6] With both medications, doses are increased only when clinically appropriate rather than automatically.

"Successful obesity treatment isn't about reaching the highest dose as quickly as possible. It's about understanding the individual sitting in front of you. Every patient's response, side effects, lifestyle and goals are different, which is why dose titration should always be personalised rather than rushed. At SwiftDoctor, we focus on finding the right dose for each patient—not simply the maximum dose."

— Dr Saira Bano, GP & Co-Founder, SwiftDoctor

What are the side effects of Mounjaro and Wegovy?

The side effects of Mounjaro and Wegovy are broadly similar, because both act on the GLP-1 system. The most common are gastrointestinal: nausea, diarrhoea, constipation, vomiting and reduced appetite. These tend to be most noticeable in the first few weeks or after a dose increase, and usually settle as the body adjusts. [1][2]

There are some differences worth knowing. In the head-to-head SURMOUNT-5 trial, most side effects in both groups were mild to moderate, but gastrointestinal side effects leading to people stopping treatment were somewhat more common with semaglutide (5.6%) than with tirzepatide (2.7%). [5] Individual tolerance varies, though, and some people find one medication easier to manage than the other.

Both also carry rarer but more serious risks that clinicians screen and monitor for, including pancreatitis and gallbladder problems, which is why treatment should always be prescribed and supervised by a qualified clinician. [1][2] Semaglutide also has well-established cardiovascular data: the SELECT trial showed a meaningful reduction in major cardiovascular events in people with obesity and existing heart disease. [7] Knowing the full range of possible side effects helps you recognise what is normal early on and what is worth flagging to a clinician.

Who is eligible for Mounjaro or Wegovy?

Eligibility criteria for Mounjaro and Wegovy are broadly the same. In the UK, both are licensed for adults with a BMI of 30 kg/m² or above, or 27 kg/m² or above with at least one weight-related health condition, such as type 2 diabetes, high blood pressure or sleep apnoea [1][2]. At SwiftDoctor, we may also prescribe these medications to people with a BMI of 25 kg/m² or above if they are in a higher-risk group, recognising the health benefits that weight loss can provide. Lower BMI thresholds also apply for people from certain ethnic backgrounds, where weight-related health risks occur at a lower BMI.

Because the licensed criteria are so similar, suitability usually comes down to clinical judgement rather than the criteria themselves. A clinician will review your medical history, current medications and any contraindications, which for both medications include a personal or family history of medullary thyroid cancer or MEN 2, and pregnancy or breastfeeding. [1][2]

Access on the NHS is more restricted than private prescribing. NICE recommends tirzepatide through a phased NHS rollout with tighter BMI thresholds, and Wegovy on the NHS requires referral to a specialist weight management service. [8][9] Checking the eligibility criteria beforehand gives you a clearer sense of where you stand before booking a consultation.

Mounjaro vs Wegovy: how does cost compare?

Cost is a practical consideration, and it changes over time as prices, doses and providers vary. Both medications are priced by dose, so monthly costs can shift as you step up through treatment, and treatment length matters too, since GLP-1 medications are used over an extended period rather than as a short course.

Rather than quote fixed figures that may quickly date, we would encourage you to check current pricing on the relevant product pages. The key principle is that cost is best weighed as one factor among several: a treatment you can sustain consistently is generally more valuable than the theoretically strongest option that becomes difficult to maintain.

How to decide which is right for you

There is no single "winner" in the Mounjaro versus Wegovy debate, and any source that declares one is oversimplifying. While the trial data gives tirzepatide an edge on average weight loss, higher-dose Wegovy has narrowed that gap, and averages tell you little about how any individual will respond. The right choice depends on your health history, your goals, how you tolerate treatment, and practical factors such as cost.

It is also worth knowing that the decision is not necessarily permanent. Some patients switch between GLP-1s, for example if one is not well tolerated or is not producing the results they had hoped for, and this can be done safely with clinical oversight. The most reliable way to decide is to discuss your specific circumstances with a clinician rather than choosing on the basis of marketing or headline figures.

     "Patients often ask me which weight loss medication is 'the best', but the reality is that there isn't a single right answer. The best medication is the one that is safest, most effective and most sustainable for that individual patient. Factors such as medical history, lifestyle, previous treatments, side effects and personal preferences all play a role. That's why every treatment plan at SwiftDoctor is personalised rather than taking a one-size-fits-all approach."

— Dr Saira Bano, GP & Co-Founder, SwiftDoctor

How SwiftDoctor supports your weight loss journey

SwiftDoctor is a doctor-led service, and our clinicians assess suitability for both Mounjaro and Wegovy rather than defaulting to a single option. That means your treatment is matched to your circumstances, whether you are starting for the first time, switching from another provider, or reconsidering after a change in cost or supply.

Support does not end with the first prescription. Our clinicians provide ongoing care throughout treatment, including dose reviews and regular check-ins, and at SwiftDoctor doses are only increased when you have reached a plateau and a higher dose is clinically appropriate. The approach is personalised, discreet and judgement-free. If you would like to explore your options, you can find out more about our weight loss treatments.

Frequently asked questions

Is Mounjaro or Wegovy more effective for weight loss?

On average, tirzepatide (Mounjaro) has produced greater weight loss than semaglutide (Wegovy) in clinical trials, including the head-to-head SURMOUNT-5 trial, where average loss was around 20.2% versus 13.7% over 72 weeks. [5] However, the newer higher-dose 7.2 mg Wegovy has narrowed this gap. [6] "More effective" on average does not mean more effective for you specifically, which is why the choice is best made with a clinician.

Can I switch from Wegovy to Mounjaro or vice versa?

Yes. Switching between the two is clinically possible and relatively common, often because of tolerability, results or supply. It should be done with clinical oversight to manage the change in dose appropriately, as the two medications are not dosed on a like-for-like basis.

Which has fewer side effects, Mounjaro or Wegovy?

Both share a similar, mainly gastrointestinal side effect profile. In the head-to-head SURMOUNT-5 trial, side effects leading to discontinuation were somewhat less common with tirzepatide (2.7%) than semaglutide (5.6%), but individual tolerance varies and some people manage one better than the other. [5]

Is Wegovy cheaper than Mounjaro?

Pricing changes over time and depends on dose and provider, so it is best to check current prices on the product pages rather than rely on a fixed figure. Cost is one factor to weigh alongside effectiveness, tolerability and how sustainable treatment is for you.

Can I get Mounjaro or Wegovy prescribed online in the UK?

Yes. Both are prescription-only medicines in the UK and can be prescribed online following a proper clinical assessment by a qualified clinician. SwiftDoctor offers a fast, discreet online consultation through which eligible patients can access either treatment, with medication delivered discreetly to your door.

Sources

[1] Electronic Medicines Compendium (eMC), "Mounjaro 2.5 mg solution for injection: Summary of Product Characteristics" (Eli Lilly), https://www.medicines.org.uk/emc/product/15484/smpc

[2] Electronic Medicines Compendium (eMC), "Wegovy 0.25 mg–2.4 mg solution for injection: Summary of Product Characteristics" (Novo Nordisk), https://www.medicines.org.uk/emc/product/13616/smpc

[3] Jastreboff AM et al., New England Journal of Medicine, "Tirzepatide Once Weekly for the Treatment of Obesity" (SURMOUNT-1), https://doi.org/10.1056/NEJMoa2206038

[4] Wilding JPH et al., New England Journal of Medicine, "Once-Weekly Semaglutide in Adults with Overweight or Obesity" (STEP 1), https://doi.org/10.1056/NEJMoa2032183

[5] Aronne LJ et al., New England Journal of Medicine, "Tirzepatide as Compared with Semaglutide for the Treatment of Obesity" (SURMOUNT-5), https://www.nejm.org/doi/full/10.1056/NEJMoa2416394

[6] MHRA / GOV.UK, "Single-dose 7.2 mg semaglutide (Wegovy) pen approved to treat adult patients with obesity", https://www.gov.uk/government/news/single-dose-72mg-semaglutide-wegovy-pen-approved-to-treat-adult-patients-with-obesity

[7] Lincoff AM et al., New England Journal of Medicine, "Semaglutide and Cardiovascular Outcomes in Obesity without Diabetes" (SELECT), https://doi.org/10.1056/NEJMoa2307563

[8] National Institute for Health and Care Excellence (NICE), "Tirzepatide for managing overweight and obesity (TA1026)", https://www.nice.org.uk/guidance/ta1026

[9] NHS England, "Weight management injections", https://www.england.nhs.uk/ourwork/prevention/obesity/medicines-for-obesity/weight-management-injections/