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
Safest Weight Loss Drugs Available in the UK
If you're looking for prescription weight loss medication in the UK, you have safe, evidence-based options available through both NHS and private routes. Mounjaro, Wegovy, and Saxenda are all prescription-only medicines licensed in the UK for weight management in adults. These medications work alongside diet and exercise to support sustainable weight loss. To see if you might be eligible, it's worth checking your BMI and discussing weight management options with your GP. This guide explains what's available, how these medications work, and how to access them safely.
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 medicines are currently licensed in the UK for weight management:
- Mounjaro (tirzepatide) — A once-weekly injection that activates two natural hormone pathways (GIP and GLP-1 agonist). Average weight loss in clinical trials was around 15–21% of body weight when combined with a reduced-calorie diet and increased physical activity.
- Wegovy (semaglutide) — A once-weekly GLP-1 injection. Clinical trials showed average weight loss of approximately 15% of body weight at the maximum dose.
- Saxenda (liraglutide) — A daily GLP-1 injection. The first licensed weight loss medication in the UK, though less commonly prescribed than the once-weekly options.
All three medications are prescription-only and require a clinical assessment before being prescribed. They are not suitable for everyone, and a healthcare professional will assess your individual health needs, medical history, and eligibility. Results vary significantly between individuals.
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 vs Private Access — How to Get Started
NHS route: Prescription weight loss medication through the NHS is typically available through specialist tier 3 weight management services. You'll need a referral from your GP, and availability varies significantly by region. Waiting lists can be lengthy in some areas, but if you're eligible, the cost is covered by the NHS.
Private route: Licensed online prescribers can assess you for prescription weight loss medication without an NHS referral. You'll need a clinical consultation, and if approved, the prescription is dispensed by a registered pharmacy. This route is faster but involves costs ranging from approximately £129–£320 per month depending on the medication and dose.
Either way, use our free BMI calculator to check your starting point, then speak to your GP about weight management options that might suit you.
- 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.
What makes these weight loss drugs safer than older options?
Mounjaro, Wegovy, and Saxenda are prescription-only medicines that have undergone rigorous clinical testing and are regulated by the MHRA. They target specific natural hormone pathways (GLP-1 and GIP) that control hunger and blood sugar, rather than acting as stimulants. Extensive safety data is available from large clinical trials, and any prescriber will assess whether each medication is appropriate for you individually.
Who is eligible for prescription weight loss medication in the UK?
Adults with a BMI of 30 kg/m² or above are generally eligible. Those with a BMI of 27–29.9 may be eligible if they have weight-related health conditions such as type 2 diabetes, high blood pressure, or cardiovascular disease. Lower BMI thresholds (27.5+) apply to people of South Asian, Chinese, Black African, or Black Caribbean heritage due to higher health risks at lower weights. A prescriber will assess your individual eligibility.
Can I get weight loss injections on the NHS?
Yes, prescription weight loss medications are available through NHS specialist weight management services (tier 3). You'll need a referral from your GP and will be assessed by a multidisciplinary team. Availability and waiting times vary significantly by region and local healthcare commissioning. If you don't qualify for NHS access or prefer faster access, private prescribing options are available.
How quickly do weight loss drugs work?
Weight loss typically begins within the first 4–8 weeks as doses are increased. Most significant results appear over 12–16 weeks once you've reached maintenance doses. The medications work best alongside a reduced-calorie diet and increased physical activity. Try our GLP-1 weight loss calculator to estimate potential results at different doses based on clinical trial data.
Are there any serious side effects I should know about?
The most common side effects are nausea, diarrhoea, and constipation — usually mild and temporary. Serious side effects are rare but can include severe stomach pain (possible pancreatitis) or gallbladder problems. A prescriber will assess your medical history and discuss risks with you. Any concerns should be reported to your healthcare provider immediately.
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.