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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Diet Injections: Your UK Weight Loss Options
Diet injections, also known as slimming injections or weight loss jabs, are prescription-only medications licensed in the UK for weight management. Three main options are currently available: Mounjaro (tirzepatide), Wegovy (semaglutide), and Saxenda (liraglutide). Each works differently and offers distinct dosing schedules. Access is available through both NHS specialist weight management services and private prescribing. This guide explains how each option works, what to expect, and how to explore access routes. Use our free BMI calculator to check your starting point, and our GLP-1 weight loss calculator to estimate potential outcomes.
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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 the Three Main Diet Injections Compare
Mounjaro (tirzepatide) is a once-weekly injection that activates two hormone pathways: GIP and GLP-1. Clinical trials showed an average weight loss of 15–21% of body weight over 72 weeks, though individual results vary significantly. The starting dose is 2.5 mg, escalating weekly to a maximum of 15 mg. Wegovy (semaglutide) is also a once-weekly injection but activates only the GLP-1 pathway. Average weight loss in clinical trials was approximately 15% of body weight. It starts at 0.25 mg and escalates to a maximum of 2.4 mg. Saxenda (liraglutide) is a daily injection (not weekly) with a maximum dose of 3 mg. Average weight loss is around 5–10% of body weight.
- Mounjaro: once weekly, dual mechanism, 2.5–15 mg
- Wegovy: once weekly, single GLP-1 mechanism, 0.25–2.4 mg
- Saxenda: once daily, single GLP-1 mechanism, 0.6–3 mg
All three require a prescription following clinical assessment. Common side effects include nausea, diarrhoea, and constipation, typically most noticeable during dose escalation and improving over time. The choice between them depends on individual health status, lifestyle preference, and prescriber recommendation.
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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.
Accessing Diet Injections in the UK
In the UK, diet injections are available through two main routes. NHS specialist services: Referral from your GP to a tier 3 or tier 4 weight management service. Eligibility typically requires a BMI of 30 or above, or 27 or above with weight-related health conditions such as type 2 diabetes, high blood pressure, or cardiovascular disease. Lower thresholds (from BMI 27.5) apply for adults of South Asian, Chinese, Black African, or Black Caribbean heritage. NHS access varies significantly by region and may involve waiting lists of several months. Private prescribing: Online consultation with a UK-licensed prescriber, typically costing £129–£320 per month depending on dose and medication. Assessment is still required to ensure clinical suitability. Both routes require genuine clinical need and ongoing health monitoring. Track your progress with our free progress tracker once you begin 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.
Which diet injection is most effective for weight loss?
In clinical trials, Mounjaro showed average weight loss of 15–21%, Wegovy approximately 15%, and Saxenda 5–10%. However, individual results vary significantly based on diet, exercise, genetics, and adherence. No single option is "most effective" for everyone — the best choice depends on your personal health profile and what your prescriber recommends after assessment.
Can I get diet injections on the NHS?
Yes, diet injections are available through NHS specialist weight management services following referral from your GP. However, availability varies by region and waiting times can be long in many areas. You must meet eligibility criteria: BMI 30 or above, or 27 or above with weight-related health conditions. Private prescribing offers faster access without NHS referral.
What's the difference between Mounjaro and Wegovy?
Mounjaro (tirzepatide) activates two hormone pathways (GIP and GLP-1), whilst Wegovy (semaglutide) activates only GLP-1. Mounjaro is injected once weekly at doses up to 15 mg; Wegovy is also once weekly but maximum dose is 2.4 mg. Clinical trial data suggests Mounjaro may achieve slightly higher average weight loss, but results vary individually.
Are diet injections safe?
All three diet injections are prescription-only medicines approved by the MHRA for weight management in UK adults. Side effects are common during dose escalation (nausea, diarrhoea) but typically improve with time. Serious side effects are rare. However, they are not suitable for pregnant women, those with personal or family history of thyroid cancer, or people with severe stomach problems. Always discuss suitability with your prescriber.
Will I keep weight off after stopping diet injections?
Weight loss achieved with diet injections is typically maintained only if lifestyle changes (diet and exercise) are sustained. Clinical evidence suggests weight may return if the injection is stopped without ongoing behaviour change. These medications are most effective as part of a comprehensive approach that includes reduced-calorie diet and increased physical activity.
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.