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
Does Amitriptyline Cause Weight Loss?
Amitriptyline is a tricyclic antidepressant commonly prescribed in the UK for depression, anxiety, and chronic pain conditions. Contrary to what some people hope, amitriptyline does not cause weight loss — in fact, it typically causes weight gain. Most people taking amitriptyline experience an increase in appetite and may gain 1–2 kg or more during treatment. If you're taking amitriptyline and concerned about your weight, your GP can discuss alternative medications or weight management strategies with you.
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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.
Why Amitriptyline Often Causes Weight Gain
Amitriptyline causes weight gain through several mechanisms. First, it increases appetite by affecting neurotransmitters in the brain — particularly serotonin and noradrenaline — which regulate hunger signals. Second, the medication can slow your metabolism slightly, meaning you burn fewer calories at rest. Third, amitriptyline may cause fluid retention, which can show as weight gain on the scales even if fat loss hasn't occurred. Most people gain weight within the first few weeks of starting amitriptyline, though the effect usually stabilises after 2–3 months.
The weight gain is not inevitable — some people experience minimal changes — but it is common enough that your GP should discuss it before prescribing. If you're already overweight or managing a weight-related condition like type 2 diabetes, amitriptyline may not be the ideal first-choice antidepressant.
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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.
Weight Management Options If You're Taking Amitriptyline
If you're on amitriptyline and concerned about weight gain, talk to your GP about your options. You might switch to an alternative antidepressant with a lower risk of weight gain — such as fluoxetine or sertraline — if your condition allows. Alternatively, you can stay on amitriptyline and manage your weight through lifestyle changes: focus on a balanced diet with reduced calories, increase physical activity, and use our free BMI calculator to track where you stand relative to NHS healthy weight guidelines.
For structured weight loss support, the NHS weight loss programme may help. If you have a BMI of 30 or above, or 27 or above with weight-related health conditions, you may also be eligible for prescription weight loss medication through your GP or NHS specialist services.
---COL_I_ALT--- Prescription Weight Loss Options in the UK ---COL_J_ALT---If you need effective weight management alongside amitriptyline, prescription weight loss medications such as GLP-1 injections (Wegovy or Mounjaro) are available through the NHS or private prescribing in the UK. These work differently from amitriptyline — they reduce appetite and support feeling fuller after smaller meals, rather than increasing hunger. In clinical trials, Wegovy (semaglutide) helped people lose an average of around 15% of their body weight, though individual results vary.
Always discuss any new medication with your GP, especially if you're already taking amitriptyline, as there may be interactions or considerations. Try our GLP-1 weight loss calculator to explore what weight loss might look like with these medications, alongside lifestyle changes.
- 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.
Will amitriptyline help me lose weight?
No. Amitriptyline typically causes weight gain, not loss. It increases appetite and can slightly slow metabolism. If weight loss is a priority for your treatment, discuss alternative antidepressants with your GP — some, like sertraline, have less impact on weight.
How much weight do people usually gain on amitriptyline?
Most people gain 1–2 kg within the first few weeks of starting amitriptyline. The weight gain usually stabilises after 2–3 months. Some people gain more, others very little — it depends on individual metabolism and lifestyle.
Can I lose weight while taking amitriptyline?
Yes, but it requires more effort because the medication works against you. Focus on a calorie deficit through diet and exercise, and use our free BMI calculator to track progress. Discuss weight management strategies with your GP.
What antidepressants don't cause weight gain?
Sertraline, fluoxetine, and citalopram are less likely to cause weight gain than amitriptyline. Some people even lose weight on these medications. Discuss options with your GP based on your specific condition and medical history.
Should I stop taking amitriptyline because of weight gain?
Never stop prescription medication without medical advice. If weight gain is a concern, talk to your GP about alternatives or weight management support. The mental health benefit of amitriptyline often outweighs the weight change.
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.