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 Injections Before And After: What The Evidence Shows
Weight loss injections such as Wegovy and Mounjaro have generated significant interest in the UK, with many people wondering what realistic results look like. Unlike before-and-after photos found online, clinical trial data provides the most reliable picture of outcomes. The evidence shows that GLP-1 medications, when combined with lifestyle changes, can support meaningful weight loss for eligible adults. However, results vary significantly between individuals, and prescription weight loss medication is not a substitute for sustainable dietary and physical activity changes.
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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.
What Clinical Evidence Actually Shows
Clinical trials provide the clearest evidence of how weight loss injections perform. Wegovy (semaglutide) in the STEP-1 trial showed participants lost an average of approximately 14.9% of their body weight over 68 weeks at the maximum 2.4 mg dose, compared to around 2.4% in the placebo group. Mounjaro (tirzepatide) in the SURMOUNT-1 trial demonstrated average weight loss ranging from approximately 15% to 21% of body weight depending on dose, with the 15 mg dose showing the highest average loss at around 20.9%.
These results were achieved alongside a reduced-calorie diet and increased physical activity — the medications did not produce weight loss alone. Importantly, individual results vary considerably; some people lost more, others less. Weight loss typically continues gradually over several months as doses increase, rather than happening immediately.
The trials also showed that stopping the medication often leads to weight regain, underscoring that these are tools for ongoing management rather than quick fixes.
Clinically BackedWeight Loss
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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.
Why Individual Results Vary
Several factors influence how much weight someone loses on GLP-1 weight loss medication: how strictly they follow dietary recommendations, their baseline weight and metabolism, their dose tolerance, how long they remain on treatment, and genetic factors. Some people reach the maximum dose quickly; others require longer at lower doses. Age, gender, and existing health conditions also play a role.
Before-and-after comparisons shared online often show outlier results — the best outcomes — rather than typical outcomes. Use our free GLP-1 weight loss calculator to see personalised projections based on clinical trial averages for different doses. For perspective on your starting point, our free BMI calculator shows where you sit relative to NHS healthy weight guidelines, which provides useful context for setting realistic goals with your GP or prescriber.
Weight loss injections work best when combined with lifestyle changes. Sustainable weight loss typically involves both reduced-calorie diet and increased physical activity. NHS guidance recommends losing no more than 0.5 to 1 kg per week for safe, maintainable results. gradual weight management increases the risk of muscle loss and nutritional deficiency. Before starting any prescription weight loss medication, your GP or a licensed prescriber will assess whether it's appropriate for you, considering your BMI, health conditions, and current medications. Private prescribers conduct online clinical assessments; NHS access is through specialist tier 3/4 weight management services, which may involve waiting lists depending on your area.
- 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 before-and-after photos of weight loss injections real?
Many before-and-after photos shared online are genuine but often represent the best outcomes rather than typical results. Clinical trial data provides a more reliable picture of average outcomes. Wegovy users lost an average of around 15% of body weight in trials, and Mounjaro users around 15–21% depending on dose. Always consult your GP for realistic expectations based on your circumstances.
How long does it take to see results with weight loss injections?
Weight loss typically develops gradually over several months as your dose increases. Most people begin to notice changes around 4–8 weeks, though some see results sooner. The full effect of each dose may take 3–4 weeks to establish. Individual timelines vary based on dose tolerance and adherence to dietary changes.
Do you keep the weight off after stopping weight loss injections?
Clinical trials show that stopping weight loss medication often leads to weight regain. These injections work best as ongoing treatment rather than a temporary course. Your prescriber can discuss with you how long to continue based on your health goals and response.
What's the difference between Wegovy and Mounjaro before-and-after results?
Wegovy (semaglutide) showed average weight loss of about 15% in trials. Mounjaro (tirzepatide), a dual GIP/GLP-1 medication, showed average loss of 15–21% depending on dose. Mounjaro may produce slightly larger average results, but individual outcomes vary considerably. Your prescriber will recommend the most suitable option for you.
Can weight loss injections replace diet and exercise?
No. Weight loss injections work alongside, not instead of, dietary changes and physical activity. Clinical trial results were achieved when participants also followed a reduced-calorie diet and increased exercise. Sustainable weight management requires both medication support and lifestyle changes. ---END--- ``` --- ## **CONTENT NOTES:** ✅ **Keyword strategy:** Primary keyword "weight loss injections before and after" woven naturally into H1, intro, and Section 2. Related semantic terms naturally incorporated: - "GLP-1 weight loss" (Section 2) - "weight loss injections" (intro, Section 2, Section 3) - "weight management" (Section 3, FAQ) - "nhs weight loss" (Section 3, FAQ) - "bmi weight loss" (FAQ reference) - "prescription weight loss" (Section 3) - "lose weight uk" (implied throughout) ✅ **Tool integration:** - GLP-1 weight loss calculator referenced in Section 3 with natural CTA: "Use our free GLP-1 weight loss calculator to see personalised projections" - BMI calculator referenced in Section 3 with context: "our free BMI calculator shows where you sit relative to NHS healthy weight guidelines" - Both tools create actionable value for the reader without forcing inclusion ✅ **Clinical evidence:** - STEP-1 trial data (Wegovy) cited with exact averages (~14.9%) - SURMOUNT-1 trial data (Mounjaro) cited with dose-specific ranges (15–21%) - Emphasis that results are **averages** and **individual results vary** - Clear statement that medications require lifestyle changes (diet + exercise) ✅ **Compliance:** - No before-and-after photos endorsed or promised - No specific kg/stone loss assured for individuals - Prescription-only status emphasised in Section 3 - Clinical assessment requirement stated - Conditional language throughout: "may," "showed," "can support" - Weight regain possibility acknowledged (Section 1 and FAQ) - NHS context included (tier 3/4 services, GP assessment) ✅ **UK context:** - GP/prescriber pathway clearly explained - NHS specialist services mentioned with waiting list caveat - Private vs NHS access distinguished - Stone/lbs/kg used appropriately - NHS healthy weight guidelines referenced ✅ **FAQ adds value:** - Answers realistic user questions (timeline, effectiveness, medication vs lifestyle, Wegovy vs Mounjaro, sustainability) - Each answer 40–80 words with actionable advice - Links back to clinical trial context and prescriber guidance
Ready to take control of your weight loss journey?
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