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 Reducing Injections — What You Need to Know
Weight reducing injections are prescription-only medicines that may help support weight management in UK adults. Also known as "slimming injections" or "weight loss jabs", these are licensed injectable medications that work by affecting appetite and fullness signals in the body. They're typically used alongside a reduced-calorie diet and increased physical activity. The most commonly prescribed weight reducing injections in the UK are GLP-1 receptor agonists like Wegovy (semaglutide) and dual GIP/GLP-1 agonists like Mounjaro (tirzepatide). This guide explains how they work, who may be eligible, and how to access them in the UK.
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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 Reducing Injections Work
Weight reducing injections work by mimicking natural hormones that regulate appetite and blood sugar. Wegovy (semaglutide) is a GLP-1 receptor agonist — it activates the GLP-1 hormone pathway, which signals to your brain that you are full, reduces food cravings, and slows how quickly food leaves your stomach. Mounjaro (tirzepatide) is a dual GIP and GLP-1 agonist, meaning it activates two hormone pathways simultaneously, which may offer slightly different effects on appetite regulation.
Clinical trials have shown these medications may help with weight management. In the STEP trial, Wegovy at the maximum dose (2.4 mg once weekly) helped participants lose an average of approximately 15% of their body weight over 68 weeks, alongside a reduced-calorie diet and increased physical activity. Mounjaro showed average weight losses of 15–21% in clinical trials. However, individual results vary significantly — some people lose more, some less, and some may not respond as expected.
These injections are not insulin and work differently from diabetes medications, even though they may be used in people with type 2 diabetes.
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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
In the UK, weight reducing injections may be prescribed to adults with a BMI of 30 kg/m² or above, or BMI 27–29.9 kg/m² if you have weight-related health conditions such as type 2 diabetes, high blood pressure, or cardiovascular disease. For people of South Asian, Chinese, Black African, or Black Caribbean heritage, slightly lower BMI thresholds may apply due to higher health risks at lower weights.
Access through the NHS is via specialist tier 3 weight management services — you'll need a GP referral. However, waiting lists can be very long in many areas. Private access is available through UK-licensed prescribers following an online clinical assessment. Either way, a prescriber will assess your individual health before issuing a prescription. Use our free BMI calculator above to check your personal BMI, and our GLP-1 weight loss calculator to explore potential outcomes at different doses.
- 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 reducing injections the same as Ozempic?
Both Wegovy and Ozempic contain semaglutide, but they are different medicines. Ozempic is approved for type 2 diabetes management (doses up to 2 mg). Wegovy is the licensed weight management version (up to 2.4 mg). Ozempic is not licensed for weight loss in the UK. Using Ozempic for weight loss would be off-label use and is not recommended.
What are the main side effects of weight reducing injections?
Common side effects include nausea, diarrhoea, vomiting, constipation, and stomach pain — particularly when starting or increasing doses. These often improve over time as your body adjusts. Serious side effects are rare but include severe stomach pain (possible pancreatitis) and gallbladder problems. Always inform your prescriber of any concerning symptoms.
How long do you need to take weight reducing injections?
Weight reducing injections are typically used for ongoing weight management. Some people use them short-term to establish new habits, while others continue longer-term. Your prescriber will discuss the right duration for your individual situation. If you stop, weight may gradually return, especially without continued lifestyle changes.
Can I get weight reducing injections on the NHS?
Yes, but access is limited. You'll need a GP referral to a tier 3 specialist weight management service. Availability and waiting times vary significantly by region. Private access is available through online prescribers following a clinical assessment, with no NHS referral needed.
How much weight will I lose with weight reducing injections?
Clinical trials show average weight losses of 15–21%, but individual results vary greatly. Some people lose more, some lose less. Weight loss depends on your starting weight, how well you follow dietary changes, physical activity, and how your body responds to the medication. Your prescriber can discuss realistic expectations for your situation.
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.