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
Weight Loss Drugs Explained — UK Health Guide
Weight loss drugs are prescription-only medications that can help some UK adults manage their weight alongside diet and exercise. The most commonly prescribed options are GLP-1 receptor agonist medications like Wegovy (semaglutide) and Mounjaro (tirzepatide), which work by reducing appetite and helping you feel fuller after smaller meals. These are not quick fixes — they're part of a comprehensive weight management approach. Access through the NHS is limited and varies by region, but they're available privately through licensed prescribers following a clinical assessment. Understanding how these drugs work and whether you might be eligible is the first step.
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.
How Weight Loss Drugs Work in the UK
GLP-1 receptor agonist medications are the main weight loss drugs currently licensed in the UK. They work by mimicking a natural hormone that helps regulate appetite and blood sugar. When you take them, they signal to your brain that you're full, slow how quickly food leaves your stomach, and reduce cravings — all of which can support eating less without feeling deprived.
- Wegovy (semaglutide): Once-weekly injection. Clinical trials showed average weight loss of around 15% of body weight over 68 weeks when combined with a reduced-calorie diet and increased physical activity.
- Mounjaro (tirzepatide): Once-weekly injection. Uses a dual mechanism (GIP and GLP-1 pathways). Average weight loss in trials ranged from 15–21% of body weight depending on dose.
- Saxenda (liraglutide): Daily injection. Earlier GLP-1 medication — still available but less commonly prescribed than once-weekly options.
Individual results vary significantly. These medications work best alongside healthy eating, regular activity, and behaviour change — not as replacements for lifestyle work.
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.
UK Eligibility and Access Routes
In the UK, prescription weight loss drugs are available through two main routes: NHS specialist services (tier 3/4 weight management programmes) or private prescribing through GPhC-registered online pharmacies. NHS access requires a referral from your GP and assessment by a specialist team — availability and waiting times vary significantly by region. Private access is faster but requires paying for treatment, typically £129–£320 per month depending on dose.
To be eligible, you generally need a BMI of 30 or above, or 27–29.9 with a weight-related health condition such as type 2 diabetes, high blood pressure, or sleep apnoea. Adults of South Asian, Chinese, Black African, or Black Caribbean heritage may qualify at slightly lower BMI thresholds due to higher health risks at lower weights. A prescriber will assess your individual circumstances and medical history before deciding whether a weight loss drug is appropriate for you.
Side Effects and What to ExpectCommon side effects of weight loss drugs include nausea, diarrhoea, constipation, and stomach discomfort — particularly during the first few weeks or when doses increase. These usually improve over time as your body adjusts. Less common but more serious side effects can include severe stomach pain (possible pancreatitis), gallbladder problems, and changes in heart rate, which require urgent medical attention.
Weight loss drugs are not suitable for everyone. They're not recommended during pregnancy or breastfeeding, for people under 18, or for those with a personal or family history of medullary thyroid cancer. If you take diabetes medications or oral contraceptives, your prescriber may need to adjust dosing. Always inform your healthcare provider of all medications and medical conditions before starting treatment.
- 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.
Are weight loss drugs available on the NHS in the UK?
Yes, but access is limited. GLP-1 medications like Wegovy and Mounjaro are approved by NICE for use within NHS specialist weight management services (tier 3/4). However, availability varies significantly by region, waiting lists can be long, and referral is required. Private prescribing is faster but requires payment.
How much weight will I lose with a weight loss drug?
Individual results vary considerably. Clinical trials showed average weight loss of around 15–21% of body weight depending on the medication and dose, achieved over several months alongside a reduced-calorie diet and increased physical activity. Some people lose more, others less. These drugs work best as part of comprehensive lifestyle change, not alone.
Are Wegovy and Ozempic the same thing?
Both contain semaglutide, but they're different products. Ozempic is approved 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 would be off-label and is not recommended.
How do I check if I'm eligible for a weight loss drug?
Generally, you need a BMI of 30 or above, or 27–29.9 with weight-related health conditions like diabetes, high blood pressure, or sleep apnoea. Use our free BMI calculator above to check your personal BMI. Your GP or a licensed prescriber can then assess your full medical history and determine eligibility.
Can I use a weight loss drug without changing my diet or exercise?
No. Weight loss medications work best alongside lifestyle changes — a reduced-calorie diet and regular physical activity. They're tools to help manage appetite and support your efforts, not replacements for healthy eating and movement. Your prescriber will discuss this as part of your treatment plan.
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.