The UK's most complete GLP-1 guide
Every Question Answered. Every Side Effect Explained.
- How GLP-1 medications work
- Mounjaro vs Wegovy compared
- Injection instructions
- Side effects & solutions
- What to eat on treatment
- FAQs answered
Free tracker included with every download this week
What Is The Best Weight Loss Medication?
There is no single "best" weight loss medication — the right choice depends on your individual health, BMI, and medical history. Three prescription-only weight loss medications are currently licensed in the UK: tirzepatide (Mounjaro), semaglutide (Wegovy), and liraglutide (Saxenda). All three work by mimicking natural hormones that regulate appetite and blood sugar. Which medication suits you best requires assessment by a GP or licensed prescriber. This guide explains how each medication works, what clinical evidence shows, and how to access weight management treatment in the UK.
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Calculate Your BMI Instantly
Enter your height and weight below. Supports both imperial (stone & lbs) and metric (kg). Results include NHS category, healthy weight range, and ethnicity adjustments.
What Is BMI and Why Does It Matter?
Body Mass Index (BMI) is the most widely used screening tool for assessing whether your weight falls within a healthy range. Used by the NHS, GPs, and weight management services across the UK, BMI provides a quick snapshot of your weight relative to your height. The formula is simple: your weight in kilograms divided by your height in metres squared (kg/m²).
While BMI isn't a perfect measure — it doesn't account for muscle mass, bone density, or fat distribution — it remains the standard first step in identifying potential weight-related health risks including type 2 diabetes, cardiovascular disease, high blood pressure, and certain cancers.
The NHS also recommends adjusted thresholds for people of South Asian, Chinese, or Black African heritage — a BMI of 23 or above is classified as overweight, and 27.5 as obese. Our calculator includes this adjustment as a one-click toggle.
How UK Weight Loss Medications Work
Weight loss medications available in the UK work by activating natural hormone pathways in the gut and brain:
- Mounjaro (tirzepatide) — a dual GIP and GLP-1 receptor agonist that activates two hormone pathways to reduce appetite and support feeling fuller after smaller meals. Clinical trials showed participants lost an average of 15–21% of their body weight.
- Wegovy (semaglutide) — a GLP-1 receptor agonist (note: Ozempic also contains semaglutide but is licensed for diabetes, not weight management in the UK). In clinical trials, Wegovy helped participants lose approximately 15% of body weight on average.
- Saxenda (liraglutide) — a once-daily GLP-1 injection, often used when weekly injections are not suitable.
All three slow how quickly food leaves the stomach and signal to the brain that you are full. Individual results vary significantly. To understand whether you may be eligible, use our free BMI calculator to check your personal BMI.
Clinically BackedWeight Loss
No appointments. No waiting rooms. Just care — from a UK-regulated online pharmacy.
How It Works
Three simple steps to understand your weight and take action.
Enter your height and weight in our free calculator. Get your BMI, NHS category, healthy weight range, and ethnicity-adjusted thresholds instantly.
If your BMI suggests you're overweight or obese, explore our GLP-1 calculators to project potential weight loss on Mounjaro or Wegovy.
Use our progress tracker to log your weight weekly, visualise your journey with charts, and stay motivated — all stored privately in your browser.
Free Weight Loss Tools & Guides
Everything you need to understand your weight, explore medication options, and track your progress — completely free.
Eligibility and How to Access Treatment
In the UK, weight loss medications are prescribed following clinical assessment. You may be eligible if you have a BMI of 30 or above, or a BMI of 27–29.9 with weight-related health conditions such as type 2 diabetes, high blood pressure, or sleep apnoea.
NHS access: Referral to a specialist tier 3 weight management service, though availability varies by region and waiting times can be lengthy.
Private access: Online consultation with a UK-licensed prescriber, available without NHS referral. A prescriber will assess your suitability based on your individual circumstances. All weight loss medications work best alongside reduced-calorie diet and increased physical activity. Track your progress with our free progress tracker.
- Dual GIP/GLP-1 receptor agonist
- Up to 22.5% body weight loss (SURMOUNT-1)
- Weekly injection, dose escalation over 20+ weeks
- Available via private prescription in the UK
- Doses: 2.5mg → 5mg → 7.5mg → 10mg → 12.5mg → 15mg
- GLP-1 receptor agonist
- Up to 15–17% body weight loss (STEP trials)
- Weekly injection, 5-step dose escalation
- NHS & private prescription available
- Doses: 0.25mg → 0.5mg → 1mg → 1.7mg → 2.4mg
Mounjaro vs Wegovy: Head-to-Head
A side-by-side comparison of the two most popular GLP-1 weight loss medications available in the UK.
| Feature | Mounjaro | Wegovy |
|---|---|---|
| Drug class | Dual GIP/GLP-1 agonist | GLP-1 agonist |
| Active ingredient | Tirzepatide | Semaglutide |
| Avg. weight loss | 15–22.5% | 12–17% |
| Key trial | SURMOUNT-1 (2022) | STEP 1 (2021) |
| Max dose | 15 mg weekly | 2.4 mg weekly |
| Escalation period | 20–32 weeks | 16–20 weeks |
| Administration | Weekly injection (pen) | Weekly injection (pen) |
| NHS availability | Private prescription only | NHS & private |
| Approx. private cost | £150–£250/month | £150–£300/month |
| Common side effects | Nausea, diarrhoea, constipation | Nausea, vomiting, diarrhoea |
Data sourced from SURMOUNT-1 and STEP 1 clinical trials. Costs are approximate and vary by provider. Always consult a prescriber.
Am I Eligible for Weight Loss Medication?
In the UK, eligibility for GLP-1 weight loss medications like Mounjaro and Wegovy is based on your BMI and overall health profile.
- BMI of 30 or above (obese)
- Age 18 or over
- No contraindicated conditions
- Committed to lifestyle changes
- BMI of 27 or above
- Plus type 2 diabetes
- Or high blood pressure
- Or obstructive sleep apnoea
Use our BMI calculator to check whether your BMI falls within the eligible range.
How We Built These Tools
Every calculator and guide on myweightcheck is built with accuracy and transparency in mind. Our BMI calculator uses the standard WHO formula with NHS-aligned category thresholds. Our GLP-1 projections are modelled on published clinical trial data from SURMOUNT and STEP studies.
All data stays on your device. We don't require sign-ups, and we don't store your health information on any server. Your progress tracker saves data locally in your browser using localStorage, so only you can see it.
We're based in the UK and our tools are designed specifically for UK users — supporting stone & lbs by default, referencing NHS guidelines, using NICE-approved medication data, and linking to GPhC-registered pharmacies.
Frequently Asked Questions
Common questions about BMI, weight loss medications, and our free UK tools.
Is there truly a "best" weight loss medication?
No single medication is best for everyone. The right choice depends on your individual health profile, BMI, any existing conditions, and how your body responds. A GP or prescriber assesses your circumstances and recommends the most suitable option. Mounjaro may be preferred for some due to its dual mechanism; Wegovy is established with extensive trial data; Saxenda may suit those who prefer daily rather than weekly injections.
How much weight can I expect to lose with weight loss medication?
Clinical trials show average weight loss of 15–21% of body weight over 68–72 weeks, depending on the medication and dose. However, individual results vary significantly. Some people lose more, others less. Results are achieved alongside a reduced-calorie diet and increased physical activity — medications are not a replacement for lifestyle changes.
What is the difference between Ozempic and Wegovy?
Both contain semaglutide, but Ozempic is licensed in the UK for type 2 diabetes management (doses up to 2mg). Wegovy is the licensed weight management version (doses up to 2.4mg). Using Ozempic for weight loss is off-label in the UK. Wegovy is the appropriate prescription choice for weight management.
How do I access weight loss medication on the NHS?
Ask your GP for a referral to your local tier 3 specialist weight management service. Eligibility criteria include BMI ≥30 or BMI 27–29.9 with weight-related health conditions. Availability and waiting times vary significantly by region. Private online prescribing is also available without NHS referral.
Are weight loss injections safe?
All three UK-licensed weight loss medications have been tested in clinical trials and monitored for safety. Common side effects include nausea, diarrhoea, and stomach pain — typically mild and reduce over time. Serious side effects are rare but can include pancreatitis. A prescriber assesses whether the medication is safe for you personally and monitors you during treatment.
Ready to take control of your weight loss journey?
Start with a free BMI check, explore your GLP-1 options, or begin tracking your progress today. No sign-up. No cost. Just results.