A complete comparison guide to GLP-1 weight loss treatments in the UK
A note on the numbers
All efficacy figures below come from separate clinical trials with different populations, durations, and protocols. They are not the result of head-to-head comparisons, with one exception noted below. Cross-trial figures give a general sense of the landscape but should not be used to predict individual outcomes or to conclude that one treatment is definitively better than another.
What they have in common
All four treatments belong to the GLP-1 receptor agonist class. They work by mimicking a natural gut hormone that acts on the brain to reduce hunger, slows gastric emptying to extend feelings of fullness, and supports blood sugar regulation. The result, when combined with dietary changes and increased physical activity, is a sustained reduction in caloric intake and, over time, meaningful weight loss.
All four are prescription-only medicines in the UK, available privately, and all require a medical assessment before prescribing. Side effect profiles across the class are broadly similar, with gastrointestinal symptoms, particularly nausea, constipation, diarrhoea, and vomiting, being the most commonly reported effects, especially when starting treatment or stepping up to a higher dose.
Where they differ
The differences that matter most in practice are mechanism, administration, dosing flexibility, and efficacy data. The table below sets these out side by side.
| Foundayo | Wegovy pill | Wegovy injection | Mounjaro | |
|---|---|---|---|---|
| Active ingredient | Orforglipron | Semaglutide | Semaglutide | Tirzepatide |
| Manufacturer | Eli Lilly | Novo Nordisk | Novo Nordisk | Eli Lilly |
| MHRA approval | 10 August 2026 | 11 June 2026 | September 2023 | March 2023 |
| How taken | Daily tablet | Daily tablet | Weekly injection | Weekly injection |
| Food restrictions | None | Empty stomach, 30 min wait | None | None |
| Storage | Room temperature | Room temperature | Refrigerated | Refrigerated |
| Average weight loss (clinical trials) | Around 12% at 72 weeks (ATTAIN-1) | Around 13.6% at 64 weeks (OASIS 4) | Around 14.9% at 68 weeks (STEP 1) | Around 20.9% at 72 weeks (SURMOUNT-1) |
| Cardiovascular risk reduction licence | No | No | Yes (SELECT trial) | No |
| Needles | No | No | Yes | Yes |
Important!
The average weight loss figures in the table above come from separate clinical trials of different durations and populations. They are not the result of direct head-to-head comparisons and should not be used to predict individual outcomes.
How the Mounjaro mechanism stands apart
Semaglutide (Wegovy) and orforglipron (Foundayo) both act on the GLP-1 receptor only. Tirzepatide (Mounjaro) acts on two receptors simultaneously: GLP-1 and GIP. The addition of GIP receptor activity appears to produce a stronger combined effect on appetite, insulin sensitivity, and metabolic function, which is reflected in its clinical trial data.
In SURMOUNT-1, participants on Mounjaro 15 mg lost an average of 20.9% of their body weight over 72 weeks, compared with around 12 to 14% for the semaglutide and orforglipron options. For people for whom the scale of weight loss is the primary consideration, this difference is clinically meaningful.
Good to know
The only published head-to-head trial between orforglipron and oral semaglutide to date, the ACHIEVE-3 trial published in The Lancet in February 2026, studied people with type 2 diabetes rather than obesity. Results from this population cannot be directly applied to people without diabetes.
The practical difference of injections vs tablets
The shift from injection to tablet removes the need for needles, refrigeration, and the weekly injection routine. For some people these are minor considerations; for others they are the deciding factor.
Between the two tablets, the practical difference is administration flexibility. The Wegovy pill must be taken first thing in the morning on an empty stomach, after at least eight hours without food, with no more than 120 ml of plain water, followed by a 30-minute wait before eating, drinking anything else, or taking other medicines. This is not optional. Semaglutide's absorption is significantly reduced if these instructions are not followed, and missing the window, even occasionally, affects how much of the medicine enters the bloodstream.
Important!
The 30-minute fasting window for the Wegovy pill is not simply a recommendation. Semaglutide's absorption is significantly reduced if food, other drinks, or medicines are taken before the window has passed. Consistent adherence to the administration instructions is one of the most important factors in the Wegovy pill's effectiveness.
Foundayo has none of these restrictions. It can be taken at any time of day, with or without food, with any amount of water. For people who travel regularly, work shifts, take thyroid medication in the morning, or simply cannot reliably maintain a fasting routine before breakfast, this is a genuine practical advantage.
Good to know
For people who take levothyroxine or other time-sensitive morning medications, the Wegovy pill's fasting requirement can create a practical conflict. Foundayo's lack of food or timing restrictions makes it a more straightforward option in this situation.
The trade-off is that the Wegovy pill has shown slightly stronger average weight loss in separate trials, around 13.6% at 64 weeks compared with around 12% at 72 weeks for Foundayo. Whether that difference is meaningful in practice depends on the individual, and neither figure is a guarantee of outcome.
Wegovy and its cardiovascular benefits
One clinically important distinction that does not always feature in discussions about GLP-1 treatments is the cardiovascular benefit licence held by the Wegovy injection. The SELECT trial, a large cardiovascular outcomes study, found that semaglutide 2.4 mg reduced the risk of major cardiovascular events by 20% in adults with overweight or obesity who had established cardiovascular disease. On the basis of this evidence, the MHRA has licensed the Wegovy injection for cardiovascular risk reduction in this specific group.
Important!
The cardiovascular risk reduction licence for the Wegovy injection applies specifically to adults with established cardiovascular disease and a BMI of 27 or above. It does not apply to the Wegovy pill, Foundayo, or Mounjaro in the UK. If cardiovascular risk reduction is a clinical priority alongside weight management, discuss this distinction with your prescriber before choosing between these treatments.
This licence does not apply to the Wegovy pill, Foundayo, or Mounjaro in the UK. For people with established cardiovascular disease who are choosing between these treatments, this distinction is worth discussing with a prescriber.
Who each option tends to suit
These are practical patterns rather than clinical recommendations. Suitability is always determined by a prescriber following an individual assessment.
Mounjaro is best suited to people who:
- Want the highest average weight loss data currently available
- Are comfortable with weekly self-injection
- Have type 2 diabetes alongside overweight or obesity, as tirzepatide is also licensed for T2D
Wegovy injection is best suited to people who:
- Prefer once-weekly dosing over daily tablets
- Have established cardiovascular disease and may benefit from the SELECT trial evidence
- Have been on oral GLP-1 treatment and prefer the injection route for convenience or efficacy
Wegovy pill is best suited to people who:
- Prefer a tablet to an injection
- Can reliably maintain the morning fasting routine
- Do not travel frequently or take morning medications that conflict with fasting
Foundayo is best suited people who:
- Prefer a tablet to an injection
- Cannot or do not want to maintain the Wegovy pill's fasting window
- Travel regularly or have a variable daily routine
- Take morning thyroid medication or other time-sensitive medicines
The limits of clinical trial data
Clinical trials measure average outcomes in controlled conditions. They cannot predict what will happen for any individual. The person who loses 20% on Mounjaro and the person who loses 8% are both inside the range of outcomes observed in the same trial.
What the numbers can do is give a realistic sense of what is typical, and help identify which treatment has the strongest evidence base for a particular goal. They are a starting point for the conversation with a prescriber, not a forecast.
The factors that most consistently predict better real-world outcomes across all four treatments are adherence, dietary changes, physical activity, and regular clinical review. A treatment that suits your daily life and that you can take consistently will almost always produce better results than one with stronger trial data that you find difficult to stick to.
Is it possible to switch between treatments?
All four treatments can be switched between, but switching requires a clinical review. Semaglutide and orforglipron are different active ingredients, so switching from the Wegovy injection to Foundayo, or vice versa, is not a straightforward dose conversion. Switching from Mounjaro to either oral option involves a change of both active ingredient and mechanism, and the average weight loss data from Mounjaro trials is generally higher, so people switching from tirzepatide to semaglutide or orforglipron should discuss realistic expectations with their prescriber before making the change.
Important!
Do not switch between GLP-1 treatments without clinical guidance. Stopping one treatment and starting another without a prescriber review risks an inappropriate starting dose, a gap in treatment, or an unrealistic expectation of outcomes if switching from a treatment with stronger average efficacy data to one with lower figures.
Switching from the Wegovy injection to the Wegovy pill is the most straightforward of these transitions, as both contain semaglutide. Even here, a prescriber should confirm the appropriate starting dose and timing.
Final thoughts
The expansion of GLP-1 treatment options in the UK over the past three years has been significant. Four distinct treatments are now MHRA-approved for weight management, covering two mechanisms, two delivery routes, and two dosing schedules. The right choice depends on the individual, and the factors that matter vary: how much weight needs to be lost, what the daily routine looks like, whether needles are an issue, what other medicines are being taken, and what the underlying health picture is.
Good to know
All four treatments work best alongside a reduced-calorie diet, increased physical activity, and regular clinical support. The medicine supports lifestyle changes; it does not replace them. People who make meaningful dietary and activity changes alongside treatment consistently achieve better and more sustained results than those who rely on the medicine alone.
None of these treatments is a substitute for dietary change and increased activity. All of them work best when used as part of a structured approach with ongoing clinical support. If you are considering any of these options, the conversation with a UK-registered prescriber is the right starting point.
FAQ
Which GLP-1 treatment produces the highest average weight loss?
Mounjaro (tirzepatide) has the highest average weight loss data of the four treatments currently available in the UK, with participants in the SURMOUNT-1 trial losing an average of 20.9% of their body weight over 72 weeks. However, all figures come from separate clinical trials and are not the result of direct head-to-head comparisons. Individual outcomes vary considerably depending on adherence, lifestyle changes, starting weight, and other factors.
What is the difference between Foundayo and the Wegovy pill?
Both are once-daily oral tablets licensed for weight management in the UK, but they contain different active ingredients. The Wegovy pill contains semaglutide and must be taken on an empty stomach first thing in the morning, with a 30-minute wait before eating or drinking. Foundayo contains orforglipron and can be taken at any time of day with no food or water restrictions. The Wegovy pill showed slightly higher average weight loss in separate clinical trials, around 13.6% at 64 weeks compared with around 12% at 72 weeks for Foundayo.
Is Mounjaro available as a tablet?
No. Mounjaro is a once-weekly subcutaneous injection. It contains tirzepatide, a different active ingredient from both semaglutide and orforglipron. Foundayo, which is manufactured by the same company, Eli Lilly, is an oral tablet but contains orforglipron, not tirzepatide.
Can I switch between these treatments?
Switching between treatments is possible but requires a clinical review. Different active ingredients mean there is no automatic dose conversion between them, and switching from a treatment with stronger average efficacy data, such as Mounjaro, to one with lower average figures should involve a conversation about realistic expectations. A UK-registered prescriber can advise on the appropriate approach for your individual circumstances.
Do I need an injection to get the best results from GLP-1 treatment?
Not necessarily. The injectable options currently have higher average weight loss data than the oral tablets, but individual response varies, and adherence matters considerably. A treatment taken consistently and that fits your daily routine will generally produce better real-world results than one with stronger trial figures that is harder to maintain. The right format depends on your individual health picture, lifestyle, and preferences.
Which treatment is best if I have cardiovascular disease?
The Wegovy injection is the only one of the four treatments currently licensed in the UK for cardiovascular risk reduction, on the basis of the SELECT trial, which showed a 20% reduction in major cardiovascular events in adults with overweight or obesity and established cardiovascular disease. This licence does not currently apply to the Wegovy pill, Foundayo, or Mounjaro. If you have established cardiovascular disease, discuss this with a prescriber before choosing between these options.
Do all four treatments cause the same side effects?
The side effect profiles are broadly similar across all four treatments, as they all act on the GLP-1 receptor. The most commonly reported effects are nausea, constipation, diarrhoea, vomiting, and abdominal discomfort, particularly when starting treatment or stepping up to a higher dose. Mounjaro, which also acts on the GIP receptor, has a broadly comparable gastrointestinal profile. Individual tolerability varies between treatments and between people, and side effects often improve after the initial adjustment period.
Are these treatments available on the NHS?
All four treatments have MHRA approval, but NHS access remains limited and subject to strict eligibility criteria. Most people currently access them via private prescription. A prescriber can advise on whether NHS access may be available for your specific circumstances.
How do I know which treatment is right for me?
There is no single right answer. The most appropriate treatment depends on your health history, the degree of weight loss needed, what other medicines you take, your daily routine, and your personal preferences around injections and dosing schedules. A UK-registered prescriber can assess your individual circumstances and advise accordingly.
The DoktorABC medical advisory board
Dr. Roland Ruiken
Medical advisor, Norway
Dr. Viktor Simunovic
Medical advisor, Croatia