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 Shots In Stomach — What Are Your Options?
Weight loss shots — also called slimming injections or weight loss jabs — are prescription medications injected into the stomach area to help manage excess weight in UK adults. The most commonly prescribed options are Mounjaro (tirzepatide), Wegovy (semaglutide), and Saxenda (liraglutide). These are GLP-1 and GIP receptor agonist medications that work by reducing appetite, helping you feel fuller after smaller meals, and supporting sustainable weight loss alongside dietary changes. They're only available on prescription following a clinical assessment by a licensed healthcare professional.
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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.
UK-Licensed Weight Loss Injection Options
Three prescription weight management injections are currently licensed in the UK:
- Mounjaro (tirzepatide) — dual GIP and GLP-1 receptor agonist, once-weekly injection, doses from 2.5 mg to 15 mg. In clinical trials, participants lost an average of 15–21% of their body weight over 72 weeks alongside a reduced-calorie diet and increased physical activity.
- Wegovy (semaglutide) — GLP-1 receptor agonist, once-weekly injection, doses from 0.25 mg to 2.4 mg. STEP trial data showed average weight loss of approximately 15% of body weight at the maximum dose.
- Saxenda (liraglutide) — GLP-1 receptor agonist, once-daily injection, doses from 0.6 mg to 3 mg. Slightly older medication with a longer track record in weight management.
All three are prescription-only medicines requiring a clinical assessment before being prescribed. Individual results vary significantly depending on adherence, lifestyle changes, and personal health factors.
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.
Eligibility and How to Access Weight Loss Injections
In the UK, you may be eligible for prescription weight loss injections if you have a BMI of 30 kg/m² or above, or a BMI of 27–29.9 kg/m² with at least one weight-related health condition (such as type 2 diabetes, prediabetes, high blood pressure, or sleep apnoea). Adults of South Asian, Chinese, Black African, or Black Caribbean heritage may have access at lower BMI thresholds due to higher health risks.
NHS access: Referral to a specialist tier 3 weight management service through your GP. Waiting times vary significantly by region. Private access: Online consultation with a UK-licensed prescriber, followed by dispensing through a GPhC-registered pharmacy if clinically appropriate. Start by calculating your BMI using our free BMI calculator to understand your eligibility status, then speak with your GP about your options.
- 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.
How do weight loss injections work in the stomach?
Weight loss shots aren't injected into your stomach itself — they're injected into the stomach area (subcutaneously into the tissue under the skin on your stomach, thigh, or upper arm). The medication enters your bloodstream and activates GLP-1 or GIP receptors in your brain and gut, reducing appetite, slowing digestion, and helping you feel fuller after smaller meals. This supports weight loss when combined with a reduced-calorie diet and physical activity.
What's the difference between Mounjaro and Wegovy?
Mounjaro (tirzepatide) activates two hormone pathways — GIP and GLP-1 — whereas Wegovy (semaglutide) activates GLP-1 only. Clinical trials suggest Mounjaro may produce slightly greater average weight loss (15–21% vs 15%), but both are effective. Maximum doses differ: Mounjaro goes up to 15 mg weekly, Wegovy to 2.4 mg weekly. The choice depends on individual suitability, assessed by your prescriber.
How much weight can I expect to lose with weight loss injections?
In clinical trials, average weight loss ranged from 15–21% of body weight over 72 weeks, depending on the medication and dose. However, individual results vary significantly based on adherence, lifestyle changes, genetics, and personal health factors. Some people lose more, some less. These injections work best alongside a reduced-calorie diet and increased physical activity — they're not a standalone solution.
Can I get weight loss injections on the NHS?
Yes, but availability varies significantly by region. NICE has approved tirzepatide (Mounjaro) and semaglutide (Wegovy) for use within NHS specialist weight management services (tier 3). Access requires referral from your GP, and waiting lists can be lengthy in many areas. Private prescribing through online consultations offers faster access for eligible adults but involves out-of-pocket costs.
What are the common side effects of weight loss injections?
Most common side effects include nausea, diarrhoea, vomiting, constipation, and stomach pain — especially when starting or increasing doses. These often reduce over time as your body adjusts. Injection site reactions, fatigue, headache, and dizziness can also occur. Serious side effects are rare but include severe stomach pain (possible pancreatitis) or gallbladder problems. Always report persistent or severe symptoms to your prescriber. Use our free progress tracker to monitor your side effects and weight loss journey alongside medical support.
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.