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
Do Immediate Weight Loss Pills Really Work?
There are no truly "immediate" weight loss pills — weight loss takes time, even with prescription medication. However, prescription weight loss medications available in the UK, such as GLP-1 injections like Wegovy (semaglutide), may help support weight management when combined with diet and exercise changes. Understanding how these medicines work, who qualifies, and what realistic timelines look like will help you make informed decisions about your weight management journey. Let's explore what's actually available for weight loss in the UK and how the process works.
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.
What Weight Loss Medications Are Available in the UK?
The UK's main prescription weight management options are GLP-1 receptor agonist injections — medicines that work with your body's natural appetite regulation systems. The most commonly discussed options are:
- Wegovy (semaglutide) — a once-weekly injection. Clinical trials (STEP-1) showed participants lost an average of approximately 15% of their body weight over 68 weeks alongside a reduced-calorie diet and increased physical activity.
- Mounjaro (tirzepatide) — a once-weekly injection with a dual mechanism. SURMOUNT trials showed average weight loss of 15–21% depending on dose.
- Saxenda (liraglutide) — a once-daily injection, approved earlier but less commonly prescribed now.
All are prescription-only medicines requiring a clinical assessment from a UK-licensed prescriber. They are not available without a valid prescription, and results vary between individuals. These medicines work best as part of comprehensive weight management UK programmes, not as standalone treatments.
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.
Realistic Timelines and What to Expect
Weight loss with prescription medication happens gradually. Most people do not see significant results in the first 1–2 weeks — it typically takes 4–8 weeks to notice meaningful changes. Initial weeks often focus on tolerating the medicine and adjusting to appetite changes.
If you're prescribed a GLP-1 injection like Wegovy, doses are increased gradually (every 4 weeks) to find your effective level. Early side effects (nausea, changes to digestion) often settle as your body adapts. Sustainable weight loss averages 0.5–1 kg per week — far slower than "immediate" weight loss, but realistic and healthier. Use our free GLP-1 weight loss calculator to see projected outcomes at different doses, and track your progress with our progress tracker as you progress through 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.
Can I get immediate weight loss pills without a prescription in the UK?
No. All clinically effective prescription weight loss medications in the UK (Wegovy, Mounjaro, Saxenda) are prescription-only and require a clinical assessment from a UK-licensed prescriber. There are no proven "over-the-counter" alternatives that provide meaningful weight loss. Anyone offering these medications without a prescription is operating illegally.
How quickly do weight loss pills work?
Most people do not see significant results in the first 2–4 weeks. Weight loss typically becomes noticeable after 4–8 weeks of consistent use. The NHS recommends safe weight loss of 0.5–1 kg per week — this is slower than "immediate" but sustainable and healthier long-term.
What's the difference between Wegovy and Ozempic?
Both contain semaglutide, but Wegovy is specifically licensed for weight management in the UK. Ozempic is licensed for type 2 diabetes (at lower doses) and is not approved for weight loss. Using Ozempic for weight loss is off-label and not recommended. Always use the medication licensed for your specific condition.
How do I access weight loss medication on the NHS?
Through tier 3 specialist weight management services. You'll need a referral from your GP, and services vary significantly by region. Waiting lists can be long. Private prescribing through UK-licensed prescribers offers faster access without an NHS referral, though at personal cost.
Are weight loss pills safe long-term?
Prescription GLP-1 medications have been studied in clinical trials lasting up to 72 weeks. Common side effects (nausea, changes to digestion) often settle over time. Serious side effects are rare but possible. Your prescriber will assess whether medication is safe for you individually. Always discuss long-term plans with your healthcare provider.
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.