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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Poor Appetite and Weight Loss — What You Need to Know
Poor appetite and unintended weight loss can signal various health conditions, from minor digestive issues to more serious underlying problems. In the UK, your GP is the first point of contact if you're experiencing appetite loss combined with weight loss. This guide explains the causes, when to seek help, and how prescription weight management medications work differently from unintended weight loss. Understanding the difference between intentional weight loss through medication and unexplained appetite changes is important for your health.
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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.
Causes of Poor Appetite and Weight Loss
Poor appetite paired with unintended weight loss can stem from several causes. Medical conditions include thyroid disorders, diabetes, depression, anxiety, and gastrointestinal issues like reflux or irritable bowel syndrome. Medications may suppress appetite as a side effect—including some blood pressure drugs, chemotherapy, and certain antibiotics. Lifestyle factors such as stress, poor sleep, excessive exercise, or restrictive dieting can trigger appetite loss. Infections and acute illness often cause temporary appetite suppression. Age-related changes affect taste and smell, reducing appetite in older adults.
If your weight loss is unintended (you're not trying to lose weight), this is different from intentional weight loss through prescription medication. Unintended weight loss of more than 5% body weight in 6–12 months warrants a GP appointment.
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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.
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GLP-1 Medications vs. Unintended Appetite Loss
GLP-1 receptor agonist medications—such as Wegovy (semaglutide)—intentionally reduce appetite as part of prescribed weight management. These are prescription-only medicines licensed in the UK for adults with a BMI of 30 or above, or 27 or above with weight-related health conditions. In the STEP clinical trials, Wegovy helped participants lose approximately 15% of their body weight on average, though individual results vary and weight loss occurs alongside reduced-calorie diet and increased physical activity.
However, if you're experiencing unintended poor appetite and weight loss, this is not the same as medication-induced appetite suppression. Always inform your GP about unexplained appetite changes so they can investigate the underlying cause.
When to See Your GP About Appetite LossContact your GP if you experience poor appetite combined with any of the following: unintended weight loss of more than 5% over 6–12 months; weight loss lasting longer than 2 weeks; severe nausea or vomiting; persistent abdominal pain; changes in bowel habits; fatigue or weakness; fever; or difficulty swallowing.
Your GP can perform blood tests, assess your medications, and refer you to specialist services if needed. If you're considering prescription weight management medication, your GP or a licensed prescriber will conduct a full clinical assessment to confirm it's appropriate for you. Use our free BMI calculator above to check your current BMI, and our GLP-1 weight loss calculator to understand how prescription medication might support your weight management goals if clinically appropriate.
- 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.
Is poor appetite a side effect of weight loss injections?
Yes. GLP-1 medications like Wegovy work partly by reducing appetite, which is the intended mechanism. If you're prescribed these medications, appetite suppression is expected and monitored by your prescriber. However, if you're experiencing unintended appetite loss without medication, this may indicate an underlying health condition and you should see your GP.
How much weight loss is concerning?
Unintended weight loss of more than 5% of your body weight over 6–12 months is considered significant and warrants GP investigation. Use our free weight converter to track your weight changes in stone, lbs, or kg, and our progress tracker to monitor patterns over time. Sudden appetite loss lasting more than 2 weeks also requires medical attention.
Can anxiety or stress cause poor appetite and weight loss?
Yes. Both anxiety and chronic stress can suppress appetite and lead to weight loss. Other psychological conditions including depression may also reduce eating and cause weight loss. Your GP can assess whether stress or mental health is contributing and refer you to appropriate support services in the UK.
Is Wegovy the same as Ozempic?
Both contain semaglutide, but Ozempic is licensed for type 2 diabetes management and is not approved for weight loss in the UK. Wegovy is the prescription-only weight management version, approved for UK adults meeting specific BMI and health criteria. If prescribed Ozempic off-label for weight loss, this would be at your prescriber's discretion.
What should I do if I have unintended weight loss?
Contact your GP to rule out medical causes such as thyroid disease, diabetes, infections, or medication side effects. Avoid restrictive dieting or excessive exercise while investigating. Your GP may order blood tests and ask about other symptoms. If appropriate, they can discuss prescription weight management options after identifying any underlying causes.
Ready to take control of your weight loss journey?
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