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Mysimba Tablets

Mysimba Tablets

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What Are Mysimba Tablets and How Do They Help With Weight Loss?

 

Mysimba tablets are a prescription-only medicine used to support weight management in adults who are obese or overweight with related health conditions. Each tablet contains two active ingredients — naltrexone hydrochloride 8 mg and bupropion hydrochloride 90 mg — which work together on specific areas of the brain to help reduce appetite and food cravings. Mysimba is not a standalone solution. It is always prescribed alongside a reduced-calorie diet and increased physical activity, as part of a structured weight management programme. If you are exploring options, you can browse our full weight loss range for additional support products.

Obesity is a complex, chronic condition affecting millions of people across the UK. According to NHS data, around 26% of adults in England are classified as obese. Managing weight through lifestyle changes alone can be incredibly difficult, and for some people, medication plays an important role in achieving meaningful, sustained results. Mysimba is one of the few licensed pharmacological options available in the UK for this purpose.

 

How Do Mysimba Tablets Work in the Body?

 

Mysimba works by targeting two distinct pathways in the brain that regulate hunger, satiety, and the reward response to food. The combination of naltrexone and bupropion produces an effect that neither drug achieves alone.

  • Bupropion stimulates pro-opiomelanocortin (POMC) neurones in the hypothalamus, which are responsible for reducing appetite and increasing energy expenditure.
  • Naltrexone blocks the auto-inhibitory feedback loop that would normally dampen the effect of bupropion on POMC neurones, thereby sustaining and amplifying the appetite-suppressing signal.
  • Together, they also act on the mesolimbic dopamine system — the brain's reward pathway — reducing the pleasure and craving associated with eating, particularly high-calorie foods.
  • This dual mechanism helps patients feel fuller sooner, experience fewer food cravings, and find it easier to maintain a calorie deficit over time.

It is worth noting that Mysimba does not affect fat absorption or metabolism directly. Its action is entirely central — meaning it works through the brain rather than the gut.

 

Who Is Suitable for Mysimba Tablets?

 

Mysimba is licensed for adults aged 18 and over. It is not appropriate for everyone, and a thorough clinical assessment is required before it can be prescribed. Your prescriber will consider your full medical history, current medications, and weight-related health risks before recommending it.

You may be a suitable candidate if you meet the following criteria:

  • BMI of 30 kg/m² or above (classified as obese)
  • BMI of 27 kg/m² or above with at least one weight-related comorbidity, such as type 2 diabetes, dyslipidaemia, or hypertension
  • You have been unable to achieve adequate weight loss through diet and exercise alone
  • You do not have any contraindications to naltrexone or bupropion (see Section 2 for full details)

Mysimba is not licensed for use in children or adolescents under 18, and it is not recommended during pregnancy or breastfeeding.

 

How Does Mysimba Compare to Other Weight Loss Medicines?

 

Feature Mysimba (naltrexone/bupropion) Orlistat
Mechanism Central — acts on brain appetite and reward pathways Peripheral — inhibits fat absorption in the gut
Route Oral tablet, twice daily Oral capsule, three times daily with meals
Common side effects Nausea, headache, insomnia, constipation Oily stools, flatulence, faecal urgency
UK prescription status Prescription only (POM) Available OTC (lower dose) and on prescription

 

How Should Mysimba Tablets Be Stored?

 

Store Mysimba tablets below 30°C in their original packaging, away from direct sunlight and moisture. Keep them out of the reach and sight of children at all times. Do not use the tablets after the expiry date printed on the pack. If you are also managing other health conditions and need support with monitoring, our diabetes monitoring collection may be useful alongside your weight management plan.

This product is a medicine. Speak to your doctor or pharmacist before using if you have an underlying medical condition or are taking other medicines.

Mysimba Tablets specifications
Treatment category Weight management / Anti-obesity
Active ingredient Naltrexone hydrochloride 8 mg, Bupropion hydrochloride 90 mg
Mechanism of action Dual central action on hypothalamic POMC neurones and mesolimbic reward pathway
Suitable for Adults aged 18+ with BMI ≥30, or BMI ≥27 with weight-related comorbidity
Pack sizes 28 tablets, 112 tablets
Strengths Naltrexone 8 mg / Bupropion 90 mg per tablet
UK classification Prescription Only Medicine (POM)
Drug class Opioid antagonist / Dopamine and noradrenaline reuptake inhibitor combination
Preparation Modified-release tablet
Route of administration Oral

Specifications of Mysimba Tablets

 

What Is Mysimba and What Is It Used For?

 

Mysimba is a prescription-only modified-release tablet containing two active substances: naltrexone hydrochloride and bupropion hydrochloride. It is used as an adjunct to a reduced-calorie diet and increased physical activity for weight management in adults. It is indicated for patients with an initial BMI of 30 kg/m² or greater, or 27 kg/m² or greater in the presence of one or more weight-related comorbidities such as type 2 diabetes, high blood pressure, or abnormal blood lipids. Mysimba tablets are not a quick fix — they are a clinically supported tool to help you make lasting changes when lifestyle measures alone have not been sufficient.

 

What Do You Need to Know Before Using Mysimba?

 

Before starting Mysimba, your prescriber will carry out a full clinical assessment. There are several important contraindications and warnings you must be aware of.

Do not take Mysimba if you:

  • Have uncontrolled high blood pressure (hypertension)
  • Have a current or past seizure disorder or epilepsy
  • Have a tumour of the central nervous system
  • Are currently going through abrupt alcohol or benzodiazepine withdrawal
  • Have been diagnosed with bipolar disorder
  • Have bulimia nervosa or anorexia nervosa (current or past)
  • Are taking monoamine oxidase inhibitors (MAOIs) or have taken them within the last 14 days
  • Are currently taking opioid medicines or opioid-containing medicines (including methadone or buprenorphine)
  • Are pregnant, planning to become pregnant, or breastfeeding
  • Are under 18 years of age
  • Have severe hepatic impairment or end-stage renal disease

Known drug interactions — tell your prescriber if you take:

  • Antidepressants (SSRIs, SNRIs, tricyclics) — increased risk of seizures and serotonin syndrome
  • Antipsychotics — bupropion may lower seizure threshold
  • Antiepileptic medicines — may reduce bupropion plasma levels
  • CYP2D6 substrates (e.g. metoprolol, flecainide, antipsychotics) — bupropion is a CYP2D6 inhibitor
  • Tamoxifen — bupropion may reduce its efficacy
  • Nicotine replacement therapy — combination may increase blood pressure
  • Alcohol — should be minimised or avoided during treatment

 

How Should You Use Mysimba?

 

Mysimba is introduced gradually over four weeks to minimise side effects, particularly nausea. Always swallow tablets whole — do not crush, chew, or break them, as this can affect the modified-release mechanism and increase the risk of adverse effects. Take each dose with food and a full glass of water.

  1. Week 1: Take one tablet every morning.
  2. Week 2: Take one tablet in the morning and one tablet in the evening.
  3. Week 3: Take two tablets in the morning and one tablet in the evening.
  4. Week 4 onwards (maintenance): Take two tablets in the morning and two tablets in the evening.
Indication Age Group Dose Frequency
Weight management (titration — week 1) Adults 18+ 1 tablet (naltrexone 8 mg / bupropion 90 mg) Once daily (morning)
Weight management (titration — week 2) Adults 18+ 1 tablet morning + 1 tablet evening Twice daily
Weight management (titration — week 3) Adults 18+ 2 tablets morning + 1 tablet evening Twice daily
Weight management (maintenance — week 4+) Adults 18+ 2 tablets morning + 2 tablets evening Twice daily (max daily dose)
Not recommended Under 18

 

What Are the Possible Side Effects of Mysimba?

 

Like all medicines, Mysimba can cause side effects, although not everyone experiences them. Many side effects are most noticeable during the dose titration phase and often improve as your body adjusts. If you are also managing digestive discomfort, our indigestion range may offer some symptomatic relief alongside your treatment.

Common side effects (affecting more than 1 in 10 people):

  • Nausea
  • Headache
  • Dizziness
  • Constipation
  • Vomiting
  • Dry mouth
  • Insomnia or sleep disturbance

Less common side effects (affecting up to 1 in 10 people):

  • Increased heart rate or palpitations
  • Increased blood pressure
  • Hot flushes
  • Tremor
  • Anxiety or irritability
  • Hyperhidrosis (excessive sweating)
  • Tinnitus
  • Taste disturbance

Serious but rare side effects — seek immediate medical attention if you experience:

  • Seizures or convulsions
  • Severe allergic reaction (rash, swelling, difficulty breathing)
  • Thoughts of self-harm or suicide — bupropion carries a warning regarding neuropsychiatric events
  • Significant rise in blood pressure

 

How Should You Store Mysimba?

 

  • Store below 30°C
  • Keep in the original blister packaging to protect from moisture
  • Do not store in the bathroom or near a heat source
  • Keep out of the reach and sight of children
  • Do not use after the expiry date printed on the pack
  • Do not dispose of medicines via wastewater or household waste — return unused tablets to your pharmacy

If you are supporting your overall health alongside weight management, you may also find our vitamins and supplements collection helpful for nutritional support during a calorie-restricted diet.

Written and reviewed by our qualified team

Your safety and success are our highest priorities. Our medical team rigorously evaluates every product and piece of advice we provide, ensuring you receive only the most effective, science-backed solutions available.

Frequently Asked Questions

Where can I buy Mysimba tablets online in the UK?

Mysimba tablets are a prescription-only medicine in the UK, which means you cannot purchase them over the counter. You can order them through a GPhC-registered online pharmacy like Cured Pharmacy after completing a clinical consultation. Our weight loss collection also includes other products that may support your journey alongside prescription treatment.

How do Mysimba tablets work in the body?

Mysimba contains naltrexone and bupropion, which act on two areas of the brain — the hypothalamus and the mesolimbic reward system. Bupropion activates appetite-suppressing neurones, while naltrexone prevents the feedback loop that would normally switch those neurones off. Together, they reduce hunger and the craving for food, particularly high-calorie options, making it easier to stick to a reduced-calorie diet.

How do I take Mysimba tablets step by step?

Mysimba is started at a low dose and increased gradually over four weeks to reduce the risk of side effects. In week one, you take one tablet each morning; by week four, the full maintenance dose is two tablets in the morning and two in the evening. Always swallow tablets whole with food and water — never crush or chew them.

What is the correct dose of Mysimba tablets?

The full maintenance dose of Mysimba is two tablets twice daily — one dose in the morning and one in the evening — giving a total daily intake of naltrexone 32 mg and bupropion 360 mg. This dose is reached after a four-week titration period. Do not exceed this dose under any circumstances.

What is the best time to take Mysimba tablets?

Mysimba should be taken with food to help reduce nausea, which is one of the most common early side effects. Taking your morning dose with breakfast and your evening dose with your main meal tends to work well for most people. Avoid taking the evening dose too close to bedtime, as bupropion can cause insomnia in some patients.

What are the most common side effects of Mysimba?

The most frequently reported side effects of Mysimba include nausea, headache, constipation, dizziness, vomiting, dry mouth, and difficulty sleeping. These tend to be most noticeable during the first few weeks of treatment and often improve as your body adjusts to the medication. Taking tablets with food can help reduce nausea significantly.

How do I manage side effects of Mysimba?

Taking Mysimba with food is the single most effective way to reduce nausea. Staying well hydrated and increasing dietary fibre can help with constipation. If side effects are persistent or severe — particularly any changes in mood, thoughts of self-harm, or a significant rise in blood pressure — contact your prescriber or pharmacist promptly. Do not stop taking Mysimba suddenly without medical advice.

Who is eligible to take Mysimba tablets?

Mysimba is licensed for adults aged 18 and over with a BMI of 30 kg/m² or above, or a BMI of 27 kg/m² or above alongside a weight-related health condition such as type 2 diabetes or hypertension. A clinical assessment is required to confirm suitability, as there are several contraindications including epilepsy, uncontrolled hypertension, and current opioid use. It is not suitable for use during pregnancy or breastfeeding.

What happens if I miss a dose of Mysimba?

If you miss a dose of Mysimba, simply skip it and take your next scheduled dose at the usual time. Never take a double dose to compensate for a missed one, as this significantly increases the risk of serious side effects including seizures. If you frequently forget doses, speak to your pharmacist about strategies to help you remember.

Can I drink alcohol while taking Mysimba?

Alcohol should be minimised or avoided entirely during treatment with Mysimba. Bupropion lowers the seizure threshold, and alcohol can further increase this risk. Additionally, abrupt alcohol withdrawal in someone who drinks heavily can trigger seizures, which is a contraindication to starting Mysimba. Speak to your prescriber honestly about your alcohol intake before beginning treatment.

What are the alternatives to Mysimba for weight loss?

The main prescription alternatives to Mysimba in the UK include orlistat (which reduces fat absorption in the gut) and GLP-1 receptor agonists such as semaglutide (Wegovy) and liraglutide (Saxenda). Each works differently and suits different patient profiles. Your prescriber will help determine which option is most appropriate based on your medical history, BMI, and any existing conditions. You can also explore our weight loss collection for supportive OTC options.

How long do you stay on Mysimba tablets?

Treatment with Mysimba is reviewed at 16 weeks. If you have not achieved at least 5% weight loss from your starting body weight by this point, your prescriber will typically recommend stopping the medication. If you have responded well, treatment may continue, with ongoing monitoring of blood pressure, weight, and tolerability at regular intervals.

Does Mysimba interact with antidepressants?

Yes — Mysimba can interact with several antidepressants, including SSRIs, SNRIs, and tricyclic antidepressants. Bupropion inhibits the CYP2D6 enzyme, which affects how many antidepressants are metabolised, and the combination can increase the risk of seizures or serotonin syndrome. Always give your prescriber a full list of all medicines you are taking, including any bought without a prescription.

Can I take Mysimba if I have type 2 diabetes?

Having type 2 diabetes is actually one of the qualifying comorbidities that can make you eligible for Mysimba at a lower BMI threshold of 27 kg/m². However, your prescriber will need to review your diabetes medications carefully, as weight loss can alter your blood glucose levels and may require dose adjustments. Our diabetes monitoring collection can help you keep track of your glucose levels during treatment.

What are the latest studies on Mysimba for weight loss?

The COR (Contrave Obesity Research) clinical trial programme, which underpinned the European Medicines Agency approval of Mysimba, demonstrated that patients taking the full maintenance dose alongside lifestyle intervention lost significantly more weight than those on placebo over 56 weeks. Responders (those losing ≥5% body weight at 16 weeks) tended to achieve greater long-term weight loss. Ongoing real-world evidence continues to support its use within the licensed indication.

How Should You Use Mysimba Tablets?

Mysimba tablets must be swallowed whole with a full glass of water. Do not crush, split, or chew them — doing so destroys the modified-release coating and can cause too much of the medicine to be released at once, increasing the risk of side effects including seizures. Always take each dose with food to help reduce nausea, particularly during the early weeks of treatment.

Follow this step-by-step guide for taking Mysimba correctly:

What Is the Correct Dose of Mysimba Tablets?

The dose of Mysimba is titrated gradually over four weeks to minimise side effects. The table below summarises the recommended dosing schedule for adults. There is no approved dose for patients under 18 years of age.

When Is the Best Time to Use Mysimba Tablets?

The morning dose is best taken with breakfast, and the evening dose with your main meal of the day. This helps reduce the likelihood of nausea, which is the most commonly reported early side effect. Avoid taking the evening dose too close to bedtime — bupropion can cause insomnia or vivid dreams in some people, so leaving a gap of at least three to four hours before sleep is sensible.

Try to take your doses at roughly the same times each day to maintain consistent blood levels of the medicine. Setting a daily reminder on your phone can help you stay on track, particularly during the titration phase when the dose is changing week by week.

How Long Can You Use Mysimba Tablets For?

Mysimba is not intended as a short-term treatment. Your prescriber will review your progress at 16 weeks. If you have lost at least 5% of your initial body weight by this point, treatment is likely to continue with ongoing monitoring. If you have not reached this threshold, your prescriber will usually advise stopping Mysimba, as continuing is unlikely to be beneficial.

Long-term use beyond 16 weeks is possible for those who respond well, but it requires regular clinical review — including blood pressure monitoring — to ensure the medicine remains safe and appropriate for you. Weight management is a long-term commitment, and Mysimba works best when combined with sustained dietary and lifestyle changes throughout the treatment period.

Do not exceed the recommended dose. If in doubt, speak to your pharmacist.

Possible Side Effects of Mysimba

Like any medicine, Mysimba can cause side effects, but not everyone gets them. Most are mild and go away as your body gets used to the tablets.

The most common side effects are:

Feeling sick (nausea)    
Headaches
Trouble sleeping (insomnia)
Dry mouth
Constipation
Dizziness

Less common side effects include:

  • Anxiety or feeling restless
  • Shaking (tremors)
  • Hot flushes or sweating more than usual
  • Changes in taste
  • Stomach pain

Serious Side Effects

Serious side effects with Mysimba are rare, but they can happen. If you notice any of these, call 999 right away or go straight to A&E.

  • Mental health changes
  • Fainting/loss of consciousness.
  • Muscle breakdown (Rhabdomyolysis)
  • Severe allergic reaction
  • Severe skin reactions
  • Liver damage
  • Manic episodes
  • Low blood sugar (hypoglycemia)
  • Notice your mood getting much worse, or have thoughts of harming yourself

Patient Information Leaflet

Important - Before taking any medication, it is always important to read the Patient Information Leaflet (PIL)

Written and reviewed by our qualified team

GPhC Number: 2233073
Tarun Kumar

Reviewed by:

Tarun Kumar

Superintendent/ Clinical Lead

📖 Find out more about our team of medical content authors and how we ensure the accuracy of our content with our content guidelines.

Content last updated: 31 Mar 2025

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