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 Sachets and Prescription Medication in the UK
Weight loss sachets and powder formulations are marketed as dietary supplements in the UK, but if you're looking for clinically proven weight management support, prescription medication may be more effective. The NHS and private prescribers offer several licensed medications for eligible adults, including injectable options and alternatives. This guide covers UK prescription weight loss options, who can access them, and how to explore what's right for your health journey. Using our free weight loss calculator, you can estimate potential outcomes with evidence-based medication.
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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 Prescription Weight Loss Medications
The UK has three prescription-only medications licensed for weight management alongside diet and exercise:
- Mounjaro (tirzepatide) — a dual GIP and GLP-1 receptor agonist, injected once weekly. Clinical trials showed participants lost an average of 15–21% of their body weight over 72 weeks.
- Wegovy (semaglutide) — a GLP-1 receptor agonist, injected once weekly at doses up to 2.4 mg. Evidence suggests average weight loss of around 15% of body weight.
- Saxenda (liraglutide) — a daily GLP-1 injection, maximum dose 3 mg. Produces modest weight loss and may help weight management when combined with lifestyle changes.
All are prescription-only and require a clinical assessment to determine eligibility. Individual results vary significantly, and these medications work best alongside a reduced-calorie diet and increased physical activity. Use our GLP-1 weight loss calculator above to explore potential outcomes at different doses.
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 Medication
You may be eligible for prescription weight loss medication if you have a BMI of 30 or above, or a BMI of 27–29.9 with weight-related health conditions such as type 2 diabetes, high blood pressure, or sleep apnoea. Lower BMI thresholds apply if you're of South Asian, Chinese, Black African, or Black Caribbean heritage.
NHS access: Ask your GP for referral to a specialist tier 3 weight management service. Availability and waiting times vary by region. Private access: Online consultations with UK-licensed prescribers followed by prescription from a GPhC-registered pharmacy. Check your BMI using our free BMI calculator, then speak with your GP or explore private options. Your weight management journey is personal — a healthcare professional can advise what's appropriate for you.
- 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 loss sachets the same as prescription weight loss injections?
No. Over-the-counter sachets and powders are dietary supplements with limited clinical evidence. Prescription medications like Mounjaro and Wegovy are licensed medicines with strong clinical trial data. Sachets may support diet but are not substitutes for prescription treatment if you're eligible.
How much weight can I expect to lose with prescription medication?
Clinical trials show average weight loss of 15–21% of body weight over several months, but individual results vary. Some people lose more, others less. Weight loss medications work best alongside a reduced-calorie diet and increased physical activity. Results depend on dose, adherence, and personal factors.
Can I get weight loss medication on the NHS?
Yes, but access is through specialist tier 3 weight management services following GP referral. Eligibility criteria apply, and availability varies significantly by region. Waiting lists can be several months. Private prescribing is an alternative for eligible adults without NHS referral.
What are the side effects of prescription weight loss injections?
Common side effects include nausea, diarrhoea, constipation, and stomach pain, particularly when starting or increasing doses. Most side effects are mild and temporary. Serious side effects are rare but can include pancreatitis. Your prescriber will discuss risks and benefits during assessment.
Do I need to take weight loss medication forever?
No. Many people use it for a defined period (typically 12–24 months) while establishing new eating and exercise habits. Some continue longer-term. Your prescriber will review progress regularly and discuss duration based on your individual health and goals.
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.