Mysimba and Mounjaro are often compared, usually on price. However, cost is not always the best place to start. For some people, the choice may already be limited by their medical history, other medicines or whether they meet the eligibility requirements for treatment.
Both are prescription only medicines in the UK. Both are licensed for use alongside a reduced calorie diet and increased physical activity, and both require a clinical assessment before treatment. Beyond that, they work in different ways. Mysimba is a weight loss tablet that acts on brain pathways involved in appetite and food reward. Mounjaro is a weekly injection containing tirzepatide, which acts on GIP and GLP 1 receptors involved in appetite and digestion.
This guide explains how each medicine works, what the clinical trials showed, who may not be able to take Mysimba, what treatment can cost, and how to compare providers if you are searching for the cheapest Mysimba UK option.
Key things to know
- Mysimba contains naltrexone and bupropion in a prolonged release tablet. Mounjaro contains tirzepatide and is given as a once weekly injection.
- In the COR trial programme, naltrexone and bupropion produced mean weight loss of roughly 5 to 9 per cent over 56 weeks, compared with 1 to 3 per cent with placebo.
- Tirzepatide's pivotal weight management trial reported average weight reductions of roughly 15 to 21 per cent, depending on the dose and study population.
- Mysimba should be stopped at 16 weeks if at least 5 per cent of starting body weight has not been lost.
- Suitability for either medicine is decided by a prescriber after an individual assessment, and results vary from person to person.
- Mysimba is thought to reduce appetite and cravings by acting on brain pathways involved in hunger and food reward.
- Unlike orlistat mysimba, which affects fat absorption in the digestive system, Mysimba acts mainly through pathways in the brain involved in appetite and food reward.
- Mysimba should not be used during pregnancy or while breastfeeding.
- Body weight, BMI and any weight related health conditions are among the factors considered when assessing suitability for Mysimba.
Mysimba vs Mounjaro at a Glance
| Mysimba | Mounjaro | |
|---|---|---|
| Active ingredients | Naltrexone and bupropion | Tirzepatide |
| Format | Prolonged release tablet, taken daily | Pre filled KwikPen, injected once weekly |
| How it works | Acts on brain pathways involved in appetite and food reward | Acts on GIP and GLP 1 hormone receptors involved in appetite and digestion |
| Trial weight loss | About 5 to 9 per cent over 56 weeks | About 15 to 21 per cent depending on dose |
| Licensed eligibility | BMI 30 or above, or 27 to under 30 with a weight related condition | Assessed against the relevant eligibility criteria at consultation |
| Formal stopping point | Stop at 16 weeks if under 5 per cent lost | No equivalent fixed stopping rule in the licence |
| Storage | Room temperature | Refrigerated before first use |
| Main exclusions | Extensive. Set out in full below | Assessed individually |
What Is Mysimba?
Mysimba is a prolonged release tablet containing two active ingredients, naltrexone and bupropion. Naltrexone is an opioid receptor antagonist that has also been used in addiction treatment. Bupropion acts on dopamine and noradrenaline pathways and is used for other medical purposes, including depression and smoking cessation in some settings.
Together, the two ingredients are thought to affect brain pathways involved in appetite and food reward. This makes the treatment approach different from medicines such as GLP 1 based treatments, which act on hormone receptors involved in appetite and digestion.
The UK licence covers adults with a BMI of 30 kg/m² or above, or a BMI of 27 kg/m² to under 30 kg/m² where a weight related condition such as type 2 diabetes, dyslipidaemia or controlled hypertension is present.
The dose is increased gradually during the first four weeks, reaching a maximum of four tablets a day, split between morning and evening. Your prescriber or the patient information leaflet will explain the dosing schedule. Do not change the dose yourself.
What Is Mounjaro?
Mounjaro is the brand name for tirzepatide. It is given once a week using a pre filled pen. Tirzepatide acts on two hormone receptors, GIP and GLP 1, which are involved in appetite regulation, feelings of fullness and digestion.
Mounjaro comes in six strengths, from 2.5mg to 15mg. Treatment starts at a lower strength and may be increased in steps at intervals of at least four weeks if your prescriber considers this appropriate. Each pen is designed to provide four weekly doses and should be refrigerated before first use.
Details of each strength appear on the Mounjaro injection pricing and strengths page.
What the Evidence Shows
Whether you search Mysimba vs Mounjaro or Mounjaro vs Mysimba, it is important to be careful when comparing their trial results. The medicines were studied in different clinical programmes, at different times and in different groups of people. The trials were not direct head to head comparisons.
For naltrexone and bupropion, the COR trial programme reported mean weight reductions of roughly 5 to 9 per cent from baseline over 56 weeks, compared with around 1 to 3 per cent in the placebo groups. This means the difference from placebo was roughly 3 to 5 percentage points in those studies. The treatment was used alongside lifestyle changes.
For tirzepatide, the main weight management trial reported average weight reductions of roughly 15 to 21 per cent, depending on the dose and study population.
These figures should not be treated as a direct prediction of what an individual person will lose. A medicine's trial results are only one part of the decision. Suitability, medical history, side effects, treatment preferences and how well someone responds can all matter.
Both medicines are intended to be used alongside diet and physical activity, and individual results can vary.
Who Cannot Take Mysimba
This is an important part of the comparison because Mysimba has several contraindications and precautions. Your medical history and current medicines need to be checked before treatment.
Mysimba should not be used in certain circumstances, including:
- Uncontrolled hypertension. Bupropion can increase blood pressure and heart rate. Controlled hypertension may be one of the weight related conditions considered when assessing eligibility.
- A history of seizures, or certain conditions or medicines that can lower the seizure threshold, including central nervous system tumours, severe head trauma and sudden withdrawal from alcohol or benzodiazepines.
- Current opioid use or acute opioid withdrawal, because naltrexone can precipitate withdrawal.
- A history of eating disorders such as anorexia nervosa or bulimia nervosa, or a history of bipolar disorder.
- Current or recent use of monoamine oxidase inhibitors. A gap of at least 14 days is required after stopping these medicines.
- End stage renal failure, severe hepatic impairment, pregnancy or breastfeeding.
There are age related considerations too. The product information advises caution in people over 65 and does not recommend Mysimba for people over 75. Dose restrictions also apply in moderate or severe renal impairment and moderate hepatic impairment.
Two risks are particularly important to understand. Bupropion has a dose related risk of seizures, reported at roughly 0.06 per cent in naltrexone and bupropion clinical trials. The product information also includes warnings about suicidal thoughts and behaviour because of the bupropion component. Speak to a healthcare professional promptly if your mood changes significantly or you experience thoughts of self harm.
Mysimba Side Effects and What Gets Monitored
How well you tolerate a medicine can be just as important as its potential effect on weight.
Commonly reported side effects with naltrexone and bupropion include nausea, headache, constipation, dizziness, dry mouth and difficulty sleeping. Nausea can be particularly noticeable while the dose is being increased.
Mysimba should be taken with food, but the product information advises avoiding high fat meals because they can increase bupropion exposure and may increase the risk of adverse effects.
Blood pressure and heart rate may need to be monitored during treatment because bupropion can affect both. Your prescriber will also consider your mental health history and any changes in mood during treatment.
Mounjaro has a different side effect profile. Gastrointestinal effects such as nausea, diarrhoea, constipation, vomiting and abdominal discomfort can occur, particularly around dose increases.
Neither medicine is automatically easier to tolerate. Your own response, medical history and other medicines all form part of the assessment.
The 16 Week Rule That Only Applies to One of Them
Mysimba has a formal stopping point in its licence. If at least 5 per cent of starting body weight has not been lost after 16 weeks of treatment, Mysimba should be discontinued because further clinically meaningful benefit is considered unlikely.
This also matters when comparing costs. Treatment reaches a defined review point after about four months, so a price comparison based on twelve months of continuous Mysimba treatment may not reflect what happens in every case.
For NHS treatment, access is more restricted. NICE technology appraisal TA494 recommends naltrexone and bupropion for adults with a BMI of 35 or above plus a weight related condition, within a specialist weight management service.
Cost: What Each One Actually Costs in the UK
Searches for mysimba cost uk, mysimba price uk, mysimba uk price, cheapest mysimba uk, mysimba uk cheapest, mysimba cheapest uk, cheapest mysimba and how much is mysimba in uk all look for a single number, but there is no single UK private price.
The same applies to searches such as 'find me the cheapest' or 'how much does it cost'.
Mysimba is available through private prescribing services, so prices can vary between pharmacies and clinics. There is no single national private price. The amount you pay may depend on the pack supplied, consultation fees, follow up reviews and delivery charges.
Prices can also change, so the current price shown by the provider during your consultation is more useful than a price quoted in an older article.
Mounjaro pricing is easier to compare because the strength and pen format are clearly defined. Standard prices are below, with the cost per weekly dose.
| Mounjaro strength | Standard price per pen | Cost per weekly dose |
|---|---|---|
| 2.5mg | £174.99 | £43.75 |
| 5mg | £204.99 | £51.25 |
| 7.5mg | £254.99 | £63.75 |
| 10mg | £274.99 | £68.75 |
| 12.5mg | £304.99 | £76.25 |
| 15mg | £323.99 | £81.00 |
Prices are correct at the time of writing, but they can change. The live checkout price always takes precedence.
One detail that is easy to miss is that four weeks is shorter than a calendar month. A full year of continuous weekly Mounjaro treatment would therefore work out at 13 pens rather than 12.
How to find the genuinely cheapest option
If you are trying to find the cheapest place to buy Mysimba, or comparing it with weight loss injections, five checks can make the comparison clearer.
- Compare the same quantity and dosing stage. A starter pack used during dose increases is not directly comparable with a maintenance supply.
- Compare standard prices rather than introductory or first order discounts, as these may only apply once.
- Add all extras: consultation or review fees, prescription charges, delivery costs and any express shipping upgrades.
- Check whether ongoing discounts depend on memberships or schemes with their own terms and conditions.
- Consider the realistic treatment period. With Mysimba, treatment may stop at 16 weeks if the required weight loss has not been achieved.
Mysimba is a prescription only weight management medicine that acts on brain pathways involved in appetite and food reward. It is intended to be used alongside a reduced calorie diet and increased physical activity.
When comparing providers, check that the pharmacy is registered with the General Pharmaceutical Council (GPhC) where applicable and that an appropriate prescribing process is followed. Be cautious of websites offering prescription only medicines without a proper clinical assessment.
Clinical trials of naltrexone and bupropion reported average weight reductions of approximately 5 to 9 per cent over 56 weeks in the COR programme, when used alongside lifestyle measures. These are trial averages and do not predict how much weight an individual will lose.
Compare treatment options on the same basis. A tablet that may be stopped at 16 weeks should not automatically be compared with an injection on the assumption that both will be used continuously for a year. Looking at the full set of weight loss treatment options and considering the likely treatment period can give you a more useful picture of cost.
Where to Buy Mysimba in the UK
Mysimba is prescription only, so searches such as buy Mysimba, buy Mysimba UK, buy Mysimba online, buy Mysimba online UK, Mysimba buy, Mysimba buy online, Mysimba buy online UK, order Mysimba, purchase Mysimba online and where can I buy Mysimba UK all refer to obtaining the medicine through an appropriate prescribing and dispensing service.
Searches for mysimba boots reflect the fact that some high street chains offer prescription services through online doctor services. Availability and pricing can vary, so check directly with the provider you are considering.
Whoever you use, these checks can help you assess whether the service follows the appropriate process:
- The pharmacy should be registered with the General Pharmaceutical Council (GPhC) where applicable, with its registration details available for verification on the official register.
- A prescriber should assess you before supply. A website that allows you to buy a prescription only medicine without an appropriate clinical assessment should be treated with caution.
- The medicine should arrive in appropriate packaging with the relevant product information, such as the patient information leaflet and batch details.
- Avoid sellers offering prescription only medicines without a prescription or clinical assessment. Medicines obtained outside the regulated supply chain may not have been stored or supplied appropriately.
Mysimba is a prescription only medicine licensed in the UK for weight management in eligible adults. It acts on brain pathways involved in appetite and food reward and is used alongside a reduced calorie diet and increased physical activity.
Eligibility is assessed individually. Broadly, the licence covers adults with a BMI of 30 kg/m² or above, or a BMI of 27 kg/m² to under 30 kg/m² where a weight related condition is present.
Mysimba is not suitable for everyone. Examples of contraindications include uncontrolled high blood pressure, a history of seizures, certain eating disorders, bipolar disorder, pregnancy and breastfeeding. Your prescriber will check your medical history and current medicines before deciding whether it is appropriate.
The dose is increased gradually over the first four weeks. The usual maintenance dose is two tablets twice daily, subject to the product information and your prescriber's instructions. Follow the instructions supplied with your medicine and do not change the dose yourself.
Clinical trials have shown that naltrexone and bupropion can support weight loss when used alongside lifestyle changes. However, individual results vary. If you do not lose at least 5 per cent of your starting weight by 16 weeks, treatment should be stopped according to the product licence.
When ordering Mysimba online, be cautious of providers offering unusually low prices without a proper clinical assessment. Tell your healthcare professional about all medicines, supplements and herbal products you take because some may interact with Mysimba.
If you experience symptoms of a serious allergic reaction, thoughts of self harm or another serious adverse reaction, seek urgent medical advice.
For those searching for the cheapest Mysimba UK option, compare prices across appropriate UK pharmacies and prescribing services. Include consultation fees, prescription charges and delivery costs rather than looking only at the advertised medicine price. Prices can vary and may change over time, so check the current price directly with the provider.
These checks can help you make a more informed comparison between legitimate services.
If you are weighing up several routes before starting treatment, explore our Weight Loss Hub for the medically supervised options available in the UK.
Practical Differences That Often Decide It
Once eligibility has been assessed, the day to day differences can become more important.
| Consideration | Mysimba | Mounjaro |
|---|---|---|
| Routine | Tablets taken several times a day, following the prescribed schedule | One injection a week on a day you choose |
| Travel | Stored at room temperature under the recommended conditions | Needs refrigeration before first use and appropriate temperature control |
| Needles | None | Injection with a fine single use pen needle |
| Dietary note | Avoid high fat meals because they can increase bupropion exposure | No equivalent high fat meal restriction in the product information, although gastrointestinal side effects can occur |
| Interactions | Several important interactions, particularly with opioids and some antidepressants | Interactions still need to be checked as part of the clinical assessment |
| Ongoing checks | Blood pressure, heart rate and other clinical factors may be monitored | Treatment response, side effects and dose changes may be reviewed |
Avoiding needles is one reason some people prefer to ask about Mysimba first, and that is a reasonable treatment preference. Mounjaro does involve a pen needle, but whether the injection format is suitable for you is something you can discuss with your prescriber.
If needles are your main concern rather than eligibility, ask your healthcare professional what the injection involves before ruling it out. It can also help to compare the practical differences between weight loss injections and tablet based treatments.
So Which One Is Right?
Neither medicine is automatically better for everyone, and an article cannot tell you which treatment is suitable for you. A clinical assessment is needed before either medicine is prescribed.
A prescriber may consider your BMI and weight related health conditions, medical history, blood pressure, seizure risk, mental health history, current medicines, previous weight management attempts and treatment preferences.
Mysimba's list of contraindications means that your medical history may rule it out before other factors are considered. If both medicines are potentially suitable, the discussion can then include how each treatment fits your routine, preferences and budget.
Mysimba acts on brain pathways involved in appetite and food reward. It is taken according to a gradually increasing dosing schedule, reaching up to four tablets a day if the prescribed maintenance dose is appropriate for you.
If you do not lose at least 5 per cent of your starting weight by 16 weeks, Mysimba should be stopped according to its product licence. This provides a clear point for reviewing whether continuing treatment is appropriate.
For people with contraindications such as uncontrolled hypertension, a history of seizures or end stage renal failure, Mysimba may not be suitable. Always speak to a healthcare professional if you develop severe or concerning side effects.
When searching for the cheapest Mysimba UK option, compare prices across appropriate UK pharmacies and prescribing services. Include consultation fees, prescription charges and delivery costs, rather than comparing the medicine price alone.
Mysimba is not routinely available through the NHS for everyone. NICE TA494 sets out specific criteria for NHS prescribing through specialist weight management services.
If you are considering Mysimba, a full clinical assessment is important to check whether it is suitable alongside lifestyle changes such as a balanced diet and regular physical activity.
Always follow your prescriber's instructions and seek advice if you have concerns about your treatment.
Treatment suitability depends on an individual assessment, and results vary between people. If you want to understand how assessment and supply work before starting, the Mounjaro injection for weight loss page sets out the process. Taking time to compare suitable treatment options can be more useful than choosing based on price alone.
Questions Worth Asking Before You Order
- What is included in the price, and are consultation, delivery and follow up reviews charged separately?
- What happens at the 16 week review if the required weight loss has not been achieved?
- How will blood pressure and any relevant mental health considerations be monitored during treatment?
- What should I do if side effects make the medicine difficult to continue?
- If treatment is stopped or changed, what happens to any unused medicine?
These questions can tell you more about a service than its headline price. If you are deciding between different treatment formats, compare the full costs, dosing schedules, eligibility requirements and monitoring involved before making a decision, including tirzepatide for weight loss and tablet based options.