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
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Weight Loss Medication Injection — How It Works in the UK
Weight loss medication injections are prescription-only medicines that may help with weight management when used alongside lifestyle changes. In the UK, the most commonly available options are GLP-1 receptor agonist medications like Wegovy (semaglutide) and Mounjaro (tirzepatide), which work by reducing appetite and helping you feel fuller after eating. Access is available through NHS specialist weight management services or private online prescribing following a clinical assessment. This guide explains how these medications work, who may be eligible, and what to expect.
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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 Injections Work and What They Are
Weight loss medication injections are prescription-only medicines that mimic natural hormones in your gut to help regulate appetite and food intake. The main types available in the UK are:
- Wegovy (semaglutide) — a GLP-1 receptor agonist, injected once weekly, maximum dose 2.4mg. Clinical trials showed an average weight loss of approximately 15% of body weight over 68 weeks alongside a reduced-calorie diet and physical activity.
- Mounjaro (tirzepatide) — a dual GIP and GLP-1 receptor agonist, injected once weekly, maximum dose 15mg. SURMOUNT trials demonstrated average weight loss of 15–21% of body weight depending on dose.
- Saxenda (liraglutide) — a GLP-1 agonist, injected once daily, maximum dose 3mg. Older medication with slightly less data than newer options.
These medications work by slowing how quickly food leaves your stomach, signalling fullness to your brain, and may reduce cravings. Individual results vary significantly — weight loss depends on the dose, your lifestyle changes, and how your body responds. They are not a substitute for diet and exercise but work best when combined with them.
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, Access Routes, and What to Expect
In the UK, weight loss medication injections may be prescribed to adults with a BMI of 30 or above, or BMI of 27–29.9 with weight-related health conditions (such as type 2 diabetes, high blood pressure, or sleep apnoea). Adults of South Asian, Chinese, Black African, or Black Caribbean heritage may be eligible at lower BMI thresholds due to higher health risks at these levels.
NHS access: Referral through your GP to a tier 3 specialist weight management service. Availability and waiting times vary significantly by region.
Private access: Online consultation with a UK-licensed prescriber, prescription dispensed by a registered pharmacy. No NHS referral needed. Costs typically range from £129–£320 per month depending on dose.
Use our free GLP-1 weight loss calculator to estimate potential outcomes at different doses, and check your BMI with our BMI calculator to understand your eligibility.
- 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 injections available on the NHS?
Yes. Mounjaro (tirzepatide) and Wegovy (semaglutide) are approved by NICE for use within NHS specialist weight management services. Access is through tier 3 services via GP referral, not standard GP prescriptions. Availability, eligibility assessment, and waiting times vary significantly by region. Contact your GP or local integrated care board to ask about services in your area.
What's the difference between Ozempic and Wegovy?
Both contain semaglutide, but Ozempic is licensed for type 2 diabetes management (doses up to 2mg) and is not approved for weight loss in the UK. Wegovy is specifically licensed for weight management with higher doses (up to 2.4mg). Using Ozempic for weight loss is off-label and not recommended. Always use the medication prescribed for the approved indication.
How much weight can you lose with these injections?
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, some less. Weight loss depends on your starting weight, the dose, how consistently you use the medication, and your lifestyle changes. These medications work best alongside a reduced-calorie diet and increased physical activity.
What are the main side effects of weight loss injections?
Common side effects include nausea, vomiting, diarrhoea, and constipation — usually most pronounced when starting or increasing doses and often reduce over time. Some people experience loss of appetite, fatigue, or stomach pain. Serious side effects are rare but may include severe stomach pain (possible pancreatitis) or gallbladder problems. Always discuss side effects with your prescriber.
Can you stop taking weight loss injections?
Yes. However, clinical evidence suggests that weight may return if you stop without maintaining dietary and lifestyle changes. Weight loss injections are a tool to support sustainable behaviour change, not a permanent solution. Discuss stopping with your prescriber, who can advise on how to transition safely and how to maintain your progress through lifestyle management.
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.