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
Best Weight Loss Pill in the UK — Prescription Options Explained
There is no single "best" weight loss pill for everyone, but the UK has several prescription-only weight management medications available following clinical assessment. If you're looking at weight loss medication in the UK, understanding your eligibility and the options available—whether through the NHS or privately—is the first step. This guide covers the prescription medications licensed for weight loss, how they work, and how to find out if you're suitable for treatment. Start by calculating your BMI using our free tool above to see where you stand health-wise.
10,000+ calculations today · NHS-aligned thresholds · 100% free
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.
UK-Licensed Weight Loss Medications
Three prescription-only medications are currently licensed in the UK for weight management in adults:
- Mounjaro (tirzepatide) — a dual GIP and GLP-1 receptor agonist given as a once-weekly injection. Clinical trials showed average weight loss of 15–21% of body weight over 72 weeks, though results vary significantly between individuals.
- Wegovy (semaglutide) — a GLP-1 receptor agonist given as a once-weekly injection. Evidence from clinical trials suggests average weight loss of around 15% of body weight, alongside a reduced-calorie diet and increased physical activity.
- Saxenda (liraglutide) — a GLP-1 receptor agonist given as a daily injection. This was the first GLP-1 licensed for weight management in the UK and remains available, though the once-weekly options are now more commonly used.
Each medication works by helping to regulate appetite and support feeling fuller after meals. All three are prescription-only and require a clinical assessment before being prescribed. Use our free GLP-1 weight loss calculator to explore potential weight loss outcomes at different doses if you're considering this type of treatment.
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.
NHS Access vs Private Prescribing — Your Options
NHS route: Weight loss medication through the NHS is available through specialist tier 3 and tier 4 weight management services. You'll need a referral from your GP, and access varies significantly by region. Waiting times can be lengthy in many areas, sometimes several months or longer depending on local availability and demand.
Private route: Prescription weight loss medication is available through private online prescribing following a clinical assessment with a UK-licensed prescriber. This route doesn't require an NHS referral and can be faster, though there is a cost. Either way, the first conversation should be with your GP. They can assess your individual health situation, discuss whether prescription medication is appropriate for you, and help guide you towards the right pathway.
- 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.
Who is eligible for prescription weight loss medication in the UK?
Adults with a BMI of 30 or above, or BMI of 27–29.9 with at least one weight-related health condition (such as type 2 diabetes, high blood pressure, or sleep apnoea) may be eligible. Lower BMI thresholds apply for people of South Asian, Chinese, Black African, or Black Caribbean heritage due to higher health risks at lower weights. A GP or prescriber will assess your individual eligibility.
How much weight can I expect to lose on weight loss medication?
Clinical trials show average weight loss of 15–21% of body weight with these medications, but individual results vary significantly. Some people lose more, others less. Weight loss medication works best alongside a reduced-calorie diet and increased physical activity. Use our free weight loss calculator to estimate potential outcomes based on dose and your starting weight.
Are weight loss pills available on the NHS?
Yes, prescription weight loss medications are available through NHS specialist weight management services, though access varies by region. You'll need a GP referral to a tier 3 or tier 4 service. Waiting times can be long in many areas. Private prescribing is also available without an NHS referral if you prefer faster access and are willing to pay privately.
What are the side effects of weight loss pills?
Common side effects include nausea, diarrhoea, constipation, and stomach pain—these are usually mild and often reduce over time. Less common side effects include headache, fatigue, and injection site reactions. Serious side effects are rare but can include pancreatitis or gallbladder problems. Your prescriber will discuss risks and benefits with you before starting treatment.
How do I find out if weight loss medication is right for me?
The best first step is to speak with your GP. They can review your health history, measure your BMI (use our free BMI calculator above for a quick check), and discuss whether prescription medication is suitable for you. Your GP can also explain NHS options and local waiting times, or discuss private prescribing alternatives if you prefer.
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.