Which GLP-1 Is Best for Weight Loss? (UK Guide 2026)
Mounjaro (tirzepatide) has shown the greatest average weight loss in clinical trials, but the best GLP-1 for you depends on tolerability, medical history, and access in the UK.
With several GLP-1 medications now available in the UK, choosing between Mounjaro, Wegovy, Ozempic, and Saxenda depends on factors including your health history, how much weight you are looking to lose, how you respond to side effects, and what is practically accessible to you.
This guide compares the main GLP-1 options used in UK weight management on the basis of clinical effectiveness, side effect profiles, convenience, and cost, so you can have a more informed conversation with your prescriber.
Quick Answer: Which GLP-1 Is Best for Weight Loss?
If you want the short version, current evidence suggests the following hierarchy.
| Priority | Recommended option |
|---|---|
| Maximum weight loss | Mounjaro (tirzepatide) |
| Best balance of effectiveness and tolerability | Wegovy (semaglutide) |
| Where weekly injections are not suitable | Saxenda (liraglutide) |
| Type 2 diabetes with weight loss as a secondary goal | Ozempic (semaglutide) |
For most people prioritising weight loss alone, tirzepatide has produced the strongest average results across major clinical trials. That said, the medication with the best outcomes for you is the one suited to your full health profile, not just the headline numbers.
GLP-1 Medications Compared for Weight Loss
| Medication | Active ingredient | Avg weight loss | Typical timeline to results | Dosing | Common side effects | Best suited for | Evidence strength | UK availability | Estimated cost |
|---|---|---|---|---|---|---|---|---|---|
| Mounjaro | Tirzepatide | ~20–22% body weight | Noticeable by 8–12 weeks | Weekly injection | Nausea, diarrhoea, reduced appetite | Maximum weight loss priority | High (large RCTs) | Private prescription; limited NHS access | £150–£250/month |
| Wegovy | Semaglutide | ~15% body weight | Noticeable by 8–12 weeks | Weekly injection | Nausea, vomiting, constipation | Balanced effectiveness and tolerability | High (large RCTs) | Private prescription; some NHS pathways | £150–£250/month |
| Ozempic | Semaglutide | ~5–10% body weight | Noticeable by 8–16 weeks | Weekly injection | Nausea, diarrhoea, fatigue | Type 2 diabetes where weight loss may also be relevant | Established | Licensed for T2D; off-label for weight loss | £80–£120/month |
| Saxenda | Liraglutide | ~5–8% body weight | Noticeable by 8–12 weeks | Daily injection | Nausea, injection site reactions, fatigue | Where weekly injections are not suitable | Established | Private prescription | £100–£200/month |
Cost estimates are approximate and vary by provider. All require a prescription following a clinical assessment.
Which GLP-1 Works Best for Weight Loss?
What clinical trials show
The clinical evidence is clearest when comparing the three active ingredients used in weight loss treatment: tirzepatide, semaglutide, and liraglutide.
Tirzepatide, the active ingredient in Mounjaro, produced high average results in the SURMOUNT-1 randomised controlled trial, with participants losing around 20–22% of their body weight on average over 72 weeks. This is partly because tirzepatide works on two hormonal pathways simultaneously, GIP and GLP-1, rather than just one. Across major studies, tirzepatide has generally produced greater average weight loss than semaglutide, although results vary between study designs and patient groups.
Semaglutide 2.4mg (Wegovy) showed an average weight loss of approximately 15% over 68 weeks in the STEP-1 trial, making it an effective option in clinical studies.
Liraglutide (Saxenda) typically produces more modest results, around 5–8% in clinical studies, and requires daily injections rather than weekly. It remains an approved and appropriate treatment for some patients, particularly where weekly injections are not suitable.
Ozempic is included here because many people compare it with Wegovy, but in the UK it is licensed for type 2 diabetes rather than weight management. Some clinicians prescribe it off-label for weight loss, although outcomes are generally less pronounced than with Wegovy because the dose used is lower.
What this means in real life
Trial averages can mask the wide variation seen between individuals. Some people lose considerably more weight than the average; others lose less. Adherence, staying on the treatment, taking doses as scheduled, and following dietary guidance, has a significant impact on outcomes.
Weight loss on these medications is also not immediate. Most people begin to see noticeable effects after four to eight weeks, with the most significant changes occurring during the first six months. Progress typically continues more gradually after that point.
Why results differ between people
Even within the same trial, weight loss outcomes vary considerably from one individual to the next. Several factors influence how much weight a person loses on a GLP-1 medication.
Dose escalation plays a role. All of these medications are started at a low dose and increased gradually over weeks or months. People who reach and tolerate the full maintenance dose may see stronger results.
Adherence matters significantly. Missing doses, stopping treatment early, or reducing the dose due to side effects all affect outcomes. The medication that a person can take consistently is often more effective in practice than one that looks better on paper.
Side effects affecting continuation are a real factor. Some people find nausea or gastrointestinal symptoms difficult enough to reduce their dose or discontinue, which limits overall weight loss regardless of the medication's potential.
Starting weight and metabolic factors also influence results. People with higher starting BMIs often lose more weight in absolute terms. Underlying metabolic conditions and how the body responds hormonally to these drugs can also vary.
Diet and activity alongside treatment make a difference. GLP-1 medications work best when combined with changes to eating habits and physical activity. Trials are conducted under structured conditions; real-world outcomes may differ.
Mounjaro vs Wegovy Weight Loss: Which Comes Out Ahead?
This is one of the most commonly asked questions about GLP-1 weight loss treatments in the UK, and the evidence points in a clear direction, with important caveats.
In terms of average weight loss seen in large-scale randomised controlled trials, tirzepatide (Mounjaro) has generally outperformed semaglutide (Wegovy). The SURMOUNT-1 data showed around 20–22% body weight reduction with tirzepatide, compared with approximately 15% with semaglutide in the STEP-1 trial. These are different studies, not head-to-head comparisons, but the difference in magnitude is clinically meaningful.
Where Wegovy may have an advantage is in its longer established track record. Semaglutide has been in clinical use for longer than tirzepatide, and its long-term safety data is more extensive. For patients where tolerability and predictability are the priority, or where tirzepatide is contraindicated, Wegovy remains an appropriate option.
The short answer: if maximum weight loss is your primary goal and you have no contraindications, current evidence may favour Mounjaro. If you want a strong, well-established treatment with a longer history of real-world use, Wegovy is a recognised alternative. A prescriber will help determine which is clinically appropriate for you.
How to Choose the Right GLP-1: A Simple Framework
If you are trying to work out where to start, this framework can help guide the conversation with your prescriber.
If your priority is maximum weight loss: Mounjaro (tirzepatide) Strong average outcomes in clinical evidence. Suitable where no contraindications exist and weekly injections are acceptable.
If you prioritise balance and predictability: Wegovy (semaglutide) Strong effectiveness with a well-established safety profile. A possible first-line choice for many patients.
If you cannot tolerate or access weekly injections: Saxenda (liraglutide) Daily dosing, more modest weight loss, but clinically appropriate for patients where other options are not suitable.
If you have type 2 diabetes: discuss Ozempic or Mounjaro with your GP Both are used in people with type 2 diabetes, though licensing and eligibility differ.
This is a starting point, not a diagnosis. Eligibility, medical history, and how you respond personally all matter. Our eligibility checker can help clarify which options may be appropriate before you speak to a prescriber.
Real-World Differences That Matter
Speed of weight loss
Some Mounjaro users may see faster initial reductions in weight compared to semaglutide-based treatments, though both require dose escalation over several weeks before reaching maintenance levels.
Appetite suppression
All GLP-1 medications work in part by reducing appetite and increasing feelings of fullness after eating. Tirzepatide's dual mechanism may produce stronger appetite suppression in some users, which may contribute to its higher average weight loss figures.
Side effects
Nausea is the most commonly reported side effect across all GLP-1 treatments, particularly during dose escalation. For most people, this improves once the body adjusts. Gastrointestinal effects, including diarrhoea, constipation, and vomiting, vary between individuals and between medications. Some people tolerate one agent better than another.
Convenience
Wegovy and Mounjaro are both administered as weekly injections, which many people find manageable. Saxenda requires a daily injection, which some find more intrusive or easier to forget.
Long-term sustainability
Weight regain after stopping GLP-1 medications is common, which is why these treatments are generally considered long-term. The medication with the best long-term profile for any given person is one they can tolerate, adhere to, and afford over time.
Which GLP-1 Is Best for You?
Consider which circumstances might apply to you.
Mounjaro may be suitable if:
- Maximising weight loss is the primary goal
- You are comfortable with a weekly injection
- You do not have a contraindication to tirzepatide
- You have access to it privately and can manage the cost
Mounjaro is currently available through private prescription in the UK. NHS access is limited and subject to specific criteria.
Wegovy may be suitable if:
- You want a strong, well-evidenced option with a longer safety track record
- You have previously tried semaglutide at lower doses (such as Ozempic) without adverse reactions
- You prefer an established weekly injection with a well-known side effect profile
Wegovy is available privately and through some NHS specialist pathways.
Saxenda may be suitable if:
- Weekly injections are not appropriate for your circumstances
- You have already been assessed as unsuitable for semaglutide or tirzepatide
- Your prescriber recommends liraglutide based on your individual health profile
Ozempic may be considered if:
- You have type 2 diabetes and weight loss is a secondary goal
- Your prescriber recommends it within a diabetes management plan
Cost and Availability in the UK
All GLP-1 weight loss medications in the UK require a prescription following a clinical assessment. Most people access these treatments through private clinics or online prescribing services, as NHS provision remains limited.
The NHS is gradually expanding access, particularly through specialist weight management services and, in some cases, primary care, but eligibility criteria apply and waiting lists can be long.
Supply constraints have affected Wegovy and Ozempic availability at various points since 2022. Mounjaro, introduced to the UK weight loss market more recently, has so far been more consistently available, though this can change. It is always worth checking current availability with your provider before starting or switching treatment.
Private monthly costs typically range from around £100 to £250 depending on the medication, dose, and provider. Some services include consultation fees within this, while others charge separately. If cost is a significant factor, this should form part of your conversation with a prescriber.
Side Effects Comparison
All GLP-1 medications share a broadly similar side effect profile, with differences in frequency and intensity between agents.
Nausea is the most common side effect and is most pronounced during the dose escalation phase. It usually improves over the first few weeks.
Diarrhoea and constipation can alternate and are among the more commonly reported gastrointestinal effects.
Fatigue is reported by some users, particularly in the early weeks.
Injection site reactions, mild redness or discomfort, can occur with all injectable treatments but are generally mild.
Rare but more serious side effects, including pancreatitis and gallbladder problems, are listed in the prescribing information for all GLP-1 agents. These should be discussed with your prescriber during assessment.
What Clinicians Consider When Prescribing
Prescribers in the UK weigh several factors when deciding which GLP-1 to recommend.
BMI and health profile: Most treatments require a BMI of 30 or above (or 27 with weight-related conditions) to qualify.
Medical history: Certain conditions, including a personal or family history of medullary thyroid carcinoma, are contraindications for some GLP-1 medications.
Diabetes status: Ozempic is licensed specifically for type 2 diabetes management. Wegovy and Mounjaro are licensed for chronic weight management in adults meeting eligibility criteria, though both are also used in people with type 2 diabetes where clinically appropriate.
Previous medication response: If you have tried a GLP-1 medication before and did not respond well, either due to ineffectiveness or poor tolerability, this will inform any switch to an alternative agent.
Patient preference: Practical factors, including injection frequency, cost, and comfort with self-administering injections, all play a part.
"Choosing between GLP-1 medicines should be a clinical decision, not just a comparison of headline weight loss figures. Tirzepatide has produced strong results in trials, but tolerability, medical history, and individual response remain just as important. The right option is the one that can be prescribed safely and used consistently over time." Alessandro Grenci, Superintendent Pharmacist at Medino
Frequently Asked Questions
Is Mounjaro better than Wegovy for weight loss?
In terms of average weight loss seen in large-scale clinical trials, tirzepatide (Mounjaro) has outperformed semaglutide (Wegovy). However, people vary considerably in how they respond, and Wegovy has a longer track record and may be better tolerated by some patients. A clinician will help determine which is more appropriate for your circumstances.
Which GLP-1 has the least side effects?
No GLP-1 medication is entirely free from side effects, and tolerance is highly individual. Saxenda (liraglutide) is sometimes better tolerated by people who find semaglutide difficult, while the reverse is also true. There is no universally "gentlest" option, it often takes a clinical assessment, and sometimes a trial period, to find the best fit.
Which GLP-1 works fastest?
Mounjaro has tended to produce faster average early weight loss than other currently available GLP-1 options in the UK in some studies, with many users seeing meaningful changes within the first two to three months. Wegovy follows a similar trajectory, though average results are somewhat lower. Saxenda tends to be slower and more modest overall.
Is Mounjaro safe for long-term use?
Current clinical evidence suggests tirzepatide is generally well tolerated over the study periods examined so far, up to 72 weeks in the main SURMOUNT-1 trial. As a relatively newer medication compared to semaglutide, its long-term real-world data is still accumulating. It is approved by the MHRA for use in the UK and is prescribed under clinical oversight. Your prescriber will review your response and any side effects at regular intervals throughout your treatment.
Can you switch between GLP-1 medications?
Yes, it is possible to switch between GLP-1 agents under clinical supervision. This is relatively common when someone does not respond adequately to one medication, experiences intolerable side effects, or when a previously unavailable treatment becomes accessible. Any switch should be managed by a prescriber.
How long do you stay on GLP-1 medication?
These medications are generally intended for long-term use. Most clinical guidance recommends continuing treatment for as long as it is working and well tolerated, as weight regain after stopping is common. Your prescriber will review your progress periodically and help you assess whether to continue.
Key Takeaway
| Medication | Best for |
|---|---|
| Mounjaro | Highest weight loss |
| Wegovy | Strongest overall balance |
| Saxenda | Alternative where weekly injections are unsuitable |
The most suitable option still depends on your health profile, how well you tolerate treatment, and what is available to you in the UK. Current evidence suggests tirzepatide leads on average weight loss effectiveness, but no medication is universally best.
Final Verdict
No GLP-1 is best for everyone, but current evidence does point to a general hierarchy for average weight loss.
- Mounjaro (tirzepatide) has produced the highest average weight loss in randomised controlled trials and may be suitable where maximum effectiveness is the priority
- Wegovy (semaglutide) is a well-evidenced, widely available alternative with a strong safety record and a slightly longer history of real-world use
- Saxenda and Ozempic have more limited roles in weight management but remain appropriate for specific patients
The right treatment is the one that fits your medical circumstances, is accessible to you in the UK, and that you can sustain over the long term. If you are unsure where to start, using an eligibility checker can help clarify which options may be appropriate before speaking to a prescriber.
