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
Three Month Weight Loss With UK Prescription Medication
Losing weight in three months is achievable with the right approach, and for many UK adults, prescription medication can support this goal alongside diet and exercise. The NHS and private prescribers now offer licensed weight management medications — including GLP-1 receptor agonist injections — for eligible adults. These medications work by reducing appetite and helping you feel fuller after smaller meals. Results vary significantly between individuals, but clinical trials show average weight losses of 15–21% over extended use. This guide explains your options, eligibility criteria, and what a realistic three-month weight loss timeline looks like with medical support.
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.
UK-Licensed Weight Loss Medications: Your Options
Three prescription weight loss medications are currently licensed in the UK for weight management. Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist — the newest option — with clinical trials showing average weight loss of 15–21% of body weight. Wegovy (semaglutide) is a GLP-1 receptor agonist, with evidence of approximately 15% average weight loss. Saxenda (liraglutide) is an older GLP-1 option requiring daily injections rather than weekly.
All three are prescription-only and require clinical assessment to determine suitability. Eligibility typically requires a BMI of 30 or above, or BMI of 27–29.9 with weight-related health conditions such as type 2 diabetes, high blood pressure, or sleep apnoea. For adults of South Asian, Chinese, Black African, or Black Caribbean heritage, lower BMI thresholds apply due to higher health risks at lower weights.
Over three months, you may lose approximately 4–8 kg (9–18 lbs) on average, though individual results vary considerably depending on dose, adherence, diet, and exercise. Our GLP-1 weight loss calculator can help you estimate 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.
NHS vs Private: Accessing Weight Loss Medication in the UK
NHS access: Available through tier 3 specialist weight management services following a GP referral. Availability varies by region, and waiting lists can be lengthy — sometimes months to over a year. Not all areas offer equal access to newer medications like Mounjaro. Ask your GP about local tier 3 services in your area.
Private access: Available through GPhC-registered online prescribing services following a clinical assessment with a UK-licensed prescriber. No waiting list, wider medication choice, and faster access — typically within days. Costs range from approximately £129–£320 monthly depending on dose and provider.
Whichever route you choose, weight loss medication works best alongside a reduced-calorie diet and increased physical activity. Use our BMI calculator to understand your starting point, and our progress tracker to monitor your three-month journey.
- 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 much weight can I realistically lose in three months with prescription medication?
Average weight loss over three months is typically 4–8 kg (9–18 lbs) on medication, though results vary significantly. Clinical trials show longer-term losses of 15–21% of body weight, but this takes 6–12 months to achieve. Individual outcomes depend on dose, diet adherence, exercise, and your starting weight. Your prescriber can give personalised projections.
Am I eligible for prescription weight loss medication on the NHS?
NHS eligibility typically requires a BMI of 30 or above, or 27–29.9 with weight-related health conditions like diabetes or high blood pressure. Access is through specialist tier 3 weight management services via GP referral. Availability varies significantly by region. Contact your GP to check local services and waiting times.
What side effects should I expect in the first three months?
Common side effects include nausea, constipation or diarrhoea, and stomach discomfort — most people experience these briefly when starting. Nausea typically peaks in week one and improves within 2–3 weeks. Serious side effects are rare but seek immediate medical attention for severe stomach pain. Always report concerns to your prescriber.
How does GLP-1 medication help with weight loss?
GLP-1 medications mimic a natural gut hormone that signals fullness to your brain, reduces appetite, and slows how quickly food leaves your stomach. This helps you eat smaller portions without constant hunger. Mounjaro (tirzepatide) also activates GIP, a second hormone pathway, which may enhance weight loss further. It's not insulin and doesn't cause low blood sugar when used alone.
Can I expect to keep weight off after three months of medication?
Weight loss is typically maintained whilst taking medication, but may return if you stop without maintaining diet and exercise changes. Weight loss medication should be used long-term alongside sustainable lifestyle changes. Ask your prescriber about ongoing treatment plans and how to transition to lifestyle-only maintenance after your three-month goal is reached.
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.