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Which GLP-1 is best for weight loss?
On average weight loss, tirzepatide (Mounjaro) is the most effective GLP-1 based treatment licensed in the UK. It is the only one tested head to head against semaglutide (Wegovy), and in that trial it produced roughly 20% average body weight reduction against about 14%. But average is not the same as best for you: the right choice depends on whether you can inject, what you can afford every month for a year or more, which side effects you can tolerate, what other conditions you have, and what your prescriber judges safe. This page compares every option licensed in the UK, honestly, including the newer tablet.
The short comparison
| Treatment | Active ingredient | Format | Average weight loss in trials |
|---|---|---|---|
| Mounjaro | Tirzepatide (GLP-1 and GIP) | Weekly injection | Around 20% at the higher doses (SURMOUNT-1) |
| Wegovy | Semaglutide | Weekly injection | Around 15% (STEP-1) |
| Foundayo | Orforglipron | Daily tablet | Around 11 to 12% in phase 3 trials |
| Saxenda | Liraglutide | Daily injection | Around 8% (SCALE) |
Trial averages are not promises. Individual results vary widely, and figures from separate trials are not directly comparable because the populations and protocols differ. The exception is noted below.
The one head-to-head trial that actually compared them
Nearly every comparison you will read stacks numbers from separate trials, which is statistically weak: different participants, different starting weights, different protocols. There is one exception worth knowing about.
SURMOUNT-5: tirzepatide versus semaglutide, directly
This trial randomised adults with obesity to tirzepatide or semaglutide and ran them side by side for 72 weeks. Tirzepatide produced substantially greater average weight loss, roughly 20% against roughly 14%. Because both arms ran under identical conditions, this is far stronger evidence than comparing SURMOUNT-1 with STEP-1 and hoping the populations matched.
What it does not tell you: which one you will tolerate, which one you can afford, or which one your prescriber considers appropriate for your medical history. It is one input, not a verdict.
Mounjaro vs Wegovy: the comparison most people actually want
| Mounjaro (tirzepatide) | Wegovy (semaglutide) | |
|---|---|---|
| How it works | Dual action on GLP-1 and GIP receptors | GLP-1 receptor only |
| Average trial weight loss | Around 20% at higher doses | Around 15% |
| Head to head | Greater average loss in SURMOUNT-5 | Lower average loss in that trial |
| Cardiovascular licensing | Not licensed in the UK specifically for cardiovascular risk reduction | Has a licensed indication for reducing cardiovascular events in eligible people with established cardiovascular disease |
| Dosing | Weekly, titrated upwards over months | Weekly, titrated upwards over months |
| Typical side effects | Nausea, constipation, diarrhoea, fatigue, injection site reactions | Very similar profile |
If you cannot or will not inject: the tablet option
This is where most comparison articles are now out of date. Until recently the honest answer in the UK was that no GLP-1 tablet was licensed for weight management, and that oral semaglutide (Rybelsus) was licensed for type 2 diabetes only. That has changed with the arrival of orforglipron, sold as Foundayo, a daily oral GLP-1 receptor agonist.
- Format: a daily tablet, with no needles, no pens and no refrigeration
- Effectiveness: phase 3 trials showed around 11 to 12% average weight loss, less than the leading injections but well ahead of older options
- Who it may suit: people with genuine needle phobia, people who travel constantly, or anyone for whom weekly injections are the barrier to starting at all
- The trade-off: you are accepting lower average weight loss in exchange for a format you can actually stick with. A tablet you take beats an injection you abandon
We track orforglipron pricing separately on Frayo, our dedicated site for this treatment.
What about Saxenda?
Saxenda (liraglutide) is the oldest option here, a daily injection producing around 8% average weight loss in the SCALE trial. It is rarely anyone’s first choice now: it requires 7 injections a week for less than half the average result of Mounjaro. It remains relevant in specific circumstances, including some adolescent prescribing where other options are not licensed, and where a prescriber has a particular reason to choose it.
Which GLP-1 is best over the counter?
None. There is no over-the-counter GLP-1 in the UK, and there never has been. Every genuine GLP-1 medicine is prescription-only, which means a qualified prescriber must assess you first. Anything sold without a prescription is not a GLP-1 medicine, whatever the packaging says.
That matters because searches for GLP-1 patches, drops, gummies and supplements have exploded, and a market has grown to meet them. To be direct about it:
- GLP-1 patches: these peptides are not absorbed through intact skin in any meaningful quantity. A patch cannot deliver a GLP-1 medicine
- GLP-1 drops and sprays: sold as “GLP-1 boosters” or “activators”. They do not contain licensed GLP-1 medicines
- GLP-1 supplements and gummies: typically fibre, berberine or similar ingredients marketed to borrow the language of prescription medicines
- Injections sold without a prescription: the genuinely dangerous category. Unlicensed and counterfeit pens circulate, dosing errors have caused serious harm, and you have no idea what is in the vial. The MHRA has repeatedly warned about this
The only weight loss medicine you can legally buy over the counter in the UK is orlistat at the lower dose (Alli), which is not a GLP-1 and works differently, by reducing fat absorption. It produces far smaller average weight loss.
Cost: the factor that decides more outcomes than efficacy
Treatment usually runs for a year or more, and price differences of £50 a month compound into hundreds of pounds. The most effective medicine is worthless if you stop after two months because of the cost, which is why we consider price a clinical-adherence issue rather than a footnote.
- Prices vary substantially between GPhC-registered pharmacies for exactly the same medicine and dose
- The cheapest pharmacy at your starting dose is often not the cheapest at your maintenance dose
- First-order discounts can mask higher ongoing prices, so compare the repeat price
- Check delivery charges and whether prices include the consultation
Last price update in our database: August 21, 2026. Compare live, dose-by-dose prices across UK pharmacies on our GLP-1 price comparison page.
Compare the clinical data yourself
Are you eligible?
UK prescribing for weight management generally requires:
- A BMI of 30 or above, or
- A BMI of 27 or above alongside a weight-related condition such as type 2 diabetes, high blood pressure, high cholesterol or obstructive sleep apnoea
- Lower BMI thresholds may apply for some ethnic groups, where risk occurs at lower body weight
Check your BMI with our free calculator, though a number alone does not determine suitability.
These treatments are not suitable for everyone. They are not prescribed in pregnancy or while breastfeeding, and are generally avoided with a personal or family history of medullary thyroid carcinoma or MEN 2, a history of pancreatitis, type 1 diabetes, severe gastrointestinal conditions such as gastroparesis, or severe kidney impairment. This list is not exhaustive; a prescriber will assess your full history.
The MHRA is clear that these medicines are for licensed medical use, not cosmetic weight loss. In January 2026 the MHRA strengthened its warnings about pancreatitis with GLP-1 medicines. Severe, persistent abdominal pain spreading to the back needs urgent medical attention: see our pancreatitis guide or call NHS 111.
Side effects: broadly similar, individually different
All GLP-1 based treatments share a similar side effect profile: nausea, constipation, diarrhoea, fatigue and injection site reactions are the common ones, usually worst after starting or increasing a dose. Tolerability varies between individuals more than between medicines, and someone who struggles on one may do better on another.
We maintain a detailed 22-guide side effect library, including an interactive symptom map: explore side effects by symptom. For eating well on treatment, see our nutrition hub.
Can you switch between them?
Yes, with prescriber supervision, and switching is common when someone plateaus, cannot tolerate side effects, or finds the cost unsustainable. Doses are not interchangeable between medicines: you do not transfer a dose level across, and most switches involve restarting at a lower dose and titrating up. Never switch, stack or self-adjust doses without your prescriber.
How to choose: five questions that decide it
- Can you commit to injections? If needles are a genuine barrier, the daily tablet may beat a “better” injection you never start
- What can you afford monthly for a year? Not the first month; the twelfth
- What else is going on medically? Established cardiovascular disease, diabetes, kidney or gastrointestinal conditions can all shift the answer
- How much weight do you need to lose? Someone targeting 5% and someone targeting 25% may reasonably choose differently
- What does your prescriber say? They see your full history, and they are the only person who can lawfully make this decision with you
Common questions
Which GLP-1 is most effective for weight loss?
Tirzepatide (Mounjaro) produces the greatest average weight loss of the treatments licensed in the UK, around 20% at higher doses, and it outperformed semaglutide in the SURMOUNT-5 head-to-head trial. Effectiveness for you personally depends on dose, tolerability, how long you continue and the lifestyle changes alongside it.
Is Mounjaro better than Wegovy?
For average weight loss, the evidence favours Mounjaro, including in the one trial that compared them directly. Wegovy holds a licensed indication for reducing cardiovascular events in eligible people with established cardiovascular disease, which can make it the better clinical choice for some. Better depends on which outcome matters most for you.
Which GLP-1 is best over the counter?
None. Every genuine GLP-1 medicine in the UK is prescription-only. GLP-1 patches, drops, gummies and supplements are not GLP-1 medicines, and injections sold without a prescription may be counterfeit or unlicensed and are genuinely dangerous. The only over-the-counter weight loss medicine in the UK is low-dose orlistat (Alli), which is not a GLP-1.
Is there a GLP-1 tablet for weight loss in the UK?
Yes. Orforglipron, sold as Foundayo, is a daily oral GLP-1 receptor agonist for weight management, with around 11 to 12% average weight loss in phase 3 trials. Oral semaglutide (Rybelsus) remains licensed for type 2 diabetes rather than weight management.
How much weight can I expect to lose?
Trial averages are roughly 20% with tirzepatide, 15% with semaglutide, 11 to 12% with orforglipron and 8% with liraglutide, but individual results vary widely around those averages. Weight loss depends on the dose reached, how long you continue, and the diet and activity changes alongside treatment.
Do I need a prescription?
Yes. All GLP-1 medicines for weight management are prescription-only in the UK, and a qualified prescriber must assess your eligibility and medical history before treatment starts. Pharmacies supplying them must be GPhC-registered.
Related guides and tools
Primary sources: Jastreboff et al., tirzepatide for obesity, New England Journal of Medicine (SURMOUNT-1) • Wilding et al., once-weekly semaglutide, NEJM (STEP-1) • SURMOUNT-5 head-to-head tirzepatide versus semaglutide • Pi-Sunyer et al., liraglutide 3.0mg, NEJM (SCALE) • NICE tirzepatide guidance • MHRA: GLP-1 medicines, what you need to know • Product information leaflets (eMC)
Published by Medstack Ltd (Company No. 16439872) under our editorial and clinical review policy. Monj does not sell, prescribe or dispense medicines. This page is information, not medical advice, and does not replace assessment by a qualified prescriber.
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