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
Free tracker included with every download this week
Slimming Injections Side Effects and How to Get Them in the UK
Slimming injections — commonly called weight loss jabs or fat jabs in the UK — are prescription-only GLP-1 and GIP medications designed to help adults lose weight. Before considering them, it's important to understand both potential side effects and how to access them through either NHS specialist services or private online consultations. This guide covers eligibility criteria, what the consultation process involves, and what to expect if you're approved for treatment.
10,000+ calculations today · NHS-aligned thresholds · 100% free
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.
Who Can Access Slimming Injections in the UK — Eligibility Criteria
To access prescription slimming injections in the UK, you must meet specific BMI thresholds and health criteria set by regulators:
- BMI of 30 or above (obese category), OR
- BMI of 27–29.9 (overweight) with at least one weight-related health condition such as type 2 diabetes, prediabetes, high blood pressure, abnormal blood lipids, obstructive sleep apnoea, or history of cardiovascular disease
For adults of South Asian, Chinese, Black African, or Black Caribbean heritage, the NHS applies lower BMI thresholds — eligibility may begin at BMI 27.5 or above because these groups face higher health risks at lower weights.
You cannot access prescription weight loss injections if you are under 18, pregnant, breastfeeding, or have certain contraindications. Your GP or a licensed prescriber will assess your individual suitability. Use our free BMI calculator above to check your personal BMI and see if you may meet initial eligibility criteria.
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.
Two Routes to Access Slimming Injections — NHS vs Private
NHS Route: Your GP can refer you to your local tier 3 specialist weight management service, where a multidisciplinary team assesses you for prescription weight loss treatment. This is free but involves waiting lists (sometimes months to years depending on region). Availability varies significantly across ICBs.
Private Route: You can access a UK-licensed prescriber through a registered online consultation service. After completing a medical assessment questionnaire, a prescriber evaluates your health and, if appropriate, issues a prescription dispensed by a GPhC-registered pharmacy. This is faster (often within days) but involves upfront costs. Both routes require a clinical assessment — weight loss injections are never available without prescription.
- 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.
What are the most common side effects of weight loss injections?
The most common side effects include nausea, diarrhoea, vomiting, constipation, and stomach pain — especially during dose adjustments. These typically reduce over time. Less common side effects include headache, fatigue, dizziness, and injection site reactions. Serious side effects like severe abdominal pain (possible pancreatitis) require immediate medical attention.
How long does it take to get slimming injections through the NHS?
NHS timelines vary significantly by region. Some specialist weight management services have waiting lists of several months to over a year. Private routes are faster — consultations can be completed within days and prescriptions issued within a week. Your local GP practice can tell you your specific NHS waiting time.
What happens during a private slimming injection consultation?
You complete a detailed medical questionnaire about your health history, current medications, weight, height, and lifestyle. A UK-licensed prescriber reviews this and may ask follow-up questions via video or message. If approved, they issue a prescription to a pharmacy. If not suitable, they'll explain why and may suggest alternatives or NHS referral.
Do I need a GP referral to access slimming injections privately?
No. Private consultations do not require a GP referral — you can book directly with a registered online prescribing service. However, it's advisable to inform your GP that you're starting weight loss medication so they can monitor your progress and adjust any other prescriptions you're taking.
Are slimming injections the same as prescription weight loss injections?
Yes. "Slimming injections", "weight loss jabs", and "fat jabs" are colloquial UK terms for prescription GLP-1 and GIP/GLP-1 medications like Wegovy (semaglutide) and Mounjaro (tirzepatide). They are medical treatments, not cosmetic injections. All require a prescription and clinical assessment. Our GLP-1 weight loss calculator can help estimate potential results at different doses.
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.