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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Loss of Weight and Night Sweats — When to Seek Help
Unexplained weight loss combined with night sweats is not normal and should never be ignored. Whilst occasional weight fluctuations are common in the UK, the combination of these two symptoms together often indicates an underlying health condition that requires medical assessment. This guide explains what may cause these symptoms, when to contact your GP, and how to track changes in your health using NHS guidance.
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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.
Common Causes of Weight Loss and Night Sweats
Several health conditions can cause both weight loss and night sweats simultaneously. Hyperthyroidism (overactive thyroid) is one of the most common causes — it speeds up your metabolism, leading to unintentional weight loss, increased sweating, and heat intolerance. Tuberculosis and other infections, though less common in the UK, classically present with both symptoms alongside fever and cough.
Lymphoma and other cancers may cause unexplained weight loss and night sweats (sometimes called "B symptoms" in medical terms). Diabetes, particularly type 2 diabetes, can trigger night sweats and may be associated with weight loss if blood sugar is poorly controlled. Anxiety and stress can also cause both symptoms, particularly if accompanied by hormonal changes. Other possibilities include autoimmune conditions such as rheumatoid arthritis, heart failure, or hormonal changes related to menopause.
The key point: if you're experiencing unexplained weight loss alongside night sweats lasting more than two weeks, book an appointment with your GP. You can use our free BMI calculator to record your baseline weight and monitor changes over time, which is helpful information to share with your healthcare provider.
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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 Guidance and When to Contact Your GP
The NHS advises that unexplained weight loss — defined as losing more than 5% of your body weight unintentionally over 6–12 months — warrants a GP appointment. Night sweats that soak your bedding or wake you from sleep, occurring regularly and without an obvious cause like a warm bedroom or infection, are also a red flag.
Contact your GP urgently if:
- You lose weight unintentionally and cannot explain it by diet or exercise changes
- Night sweats are persistent and severe, disrupting sleep
- You have fever, persistent cough, or other symptoms alongside these changes
- You notice swollen lymph nodes, fatigue, or bruising
Your GP may arrange blood tests, imaging, or specialist referrals depending on your symptoms. Track your weight using our free weight converter and BMI calculator to show your GP the pattern of change — this information is valuable for diagnosis.
- 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.
What is the difference between night sweats and normal sweating?
Normal sweating cools your body during heat or exercise. Night sweats are episodes of profuse sweating that soak your bedding or clothes, happen without clear external cause, and often occur during sleep. They're most concerning when recurring and causing sleep disruption.
Could my weight loss and night sweats be from stress or anxiety?
Yes — stress and anxiety can trigger both symptoms. Anxiety increases metabolism and can cause weight loss; stress hormones can trigger night sweats. However, persistent symptoms warrant GP assessment to rule out other causes, particularly if lasting more than two weeks.
Is unexplained weight loss always serious?
Not always, but it requires investigation. Unintentional loss of more than 5% of body weight in 6–12 months should be evaluated by your GP. Causes range from treatable conditions like thyroid disorders to lifestyle factors, but professional assessment is essential.
Should I try to gain weight back while experiencing night sweats?
Your first step should be a GP appointment, not self-management. Once a cause is identified, your GP can advise whether weight gain is appropriate or if treating the underlying condition is the priority. Attempting to gain weight without diagnosis may mask important symptoms.
How can I track weight changes to discuss with my GP?
Monitor your weight weekly using consistent scales, at the same time of day, wearing similar clothing. Record in stone/kilograms and note any patterns. Our free weight converter helps track changes across units, and you can use the BMI calculator to record measurements your GP will recognise.
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.