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
Levothyroxine and Weight Loss — What You Need to Know
Levothyroxine (a thyroid hormone replacement) is not a weight loss medication, even at 25 mcg doses. It's prescribed for hypothyroidism — an underactive thyroid. If you're looking for prescription weight loss medication in the UK, you have access to evidence-based options like Mounjaro, Wegovy, and Saxenda through NHS specialist services or private prescribing. This guide explains the difference and shows you how to access weight management uk treatment if you're eligible.
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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 Medications — Your Options
If you're seeking prescription weight loss medication in the UK, three medications are currently licensed for weight management:
- Mounjaro (tirzepatide) — a dual GIP/GLP-1 receptor agonist; starting dose 2.5 mg, maximum 15 mg once weekly. Clinical trials showed average weight loss of 15–21% body weight alongside lifestyle changes.
- Wegovy (semaglutide) — a GLP-1 receptor agonist; doses from 0.25 mg up to 2.4 mg once weekly. Average weight loss in trials was approximately 14.9% body weight.
- Saxenda (liraglutide) — a GLP-1 receptor agonist; daily injection, doses 0.6–3 mg. Older option, still available and licensed in the UK.
All three require a clinical assessment and prescription. Individual results vary and depend on adherence, diet, and activity level. Use our free GLP-1 weight loss calculator above to explore projected 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 Access — How to Get Started
In the UK, prescription weight loss medication is available through two routes:
- NHS route: Referral from your GP to a specialist tier 3 weight management service. Eligibility: BMI 30+ or BMI 27–29.9 with weight-related health conditions (type 2 diabetes, high blood pressure, sleep apnoea). Lower BMI thresholds apply for South Asian, Black African, and Black Caribbean adults. Waiting lists vary significantly by region.
- Private route: Online consultation with a UK-licensed prescriber, followed by prescription from a GPhC-registered pharmacy. No referral needed; available within days rather than months.
Start by discussing your health and weight management goals with your GP. They can assess whether you meet eligibility criteria and discuss the best pathway 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.
Can levothyroxine 25 mcg help you lose weight?
Levothyroxine is a thyroid hormone replacement prescribed for hypothyroidism, not for weight loss. At any dose, including 25 mcg, it only helps weight loss if your underactive thyroid is the cause of weight gain. Once your thyroid is properly a UK pharmacy, weight typically normalises. It should never be used off-label for weight loss in people without hypothyroidism.
What is the difference between levothyroxine and weight loss injections?
Levothyroxine replaces thyroid hormone in people with hypothyroidism. Weight loss injections (Mounjaro, Wegovy, Saxenda) are GLP-1 or GIP/GLP-1 receptor agonists that work on appetite and blood sugar regulation. They are prescribed specifically for weight management in eligible adults. They work through different mechanisms entirely.
How do I check if I'm eligible for prescription weight loss medication in the UK?
You're potentially eligible if you have a BMI of 30 or above, or BMI 27–29.9 with a weight-related health condition (diabetes, hypertension, sleep apnoea). Use our free BMI calculator above to check your BMI instantly. Then discuss eligibility with your GP, who can refer you to specialist weight management services or advise on private options.
What is the NHS weight loss pathway in the UK?
The NHS uses a four-tier system. Tier 1 is self-help and digital tools. Tier 2 is primary care-based programmes. Tier 3 (specialist multidisciplinary services) is where prescription weight loss medication may be offered. Tier 4 is bariatric surgery for severe obesity. Access and waiting times vary by region.
Can I get weight loss injections privately if I don't qualify for NHS treatment?
Yes. Private online prescribing services exist in the UK and assess eligibility independently. Following an online consultation with a UK-licensed prescriber, eligible individuals can receive a prescription dispensed by a GPhC-registered pharmacy. This route typically offers faster access than NHS specialist services, though costs apply (roughly £129–£320 per month depending on dose).
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.