Mysimba
In brief
- Mysimba is a prescription-only medicine in the UK and must normally be obtained from a pharmacy with a prescription.
- Mysimba is used as an adjunct to a reduced-calorie diet and increased physical activity for adults with BMI ≥30 kg/m² or ≥27 kg/m² with weight-related comorbidities; it combines naltrexone (an opioid antagonist) and bupropion (a noradrenaline–dopamine reuptake inhibitor) to reduce appetite and alter reward-related eating behaviour.
- The usual dosing regimen is a 4-week escalation: week 1 one tablet in the morning; week 2 one morning and one evening; week 3 two morning and one evening; week 4 onward two morning and two evening (maximum 4 tablets daily = 32 mg naltrexone / 360 mg bupropion), with assessment at 16 weeks and discontinuation if weight loss <5%.
- Form of administration: oral film‑coated tablets (8 mg naltrexone / 90 mg bupropion per tablet).
- Onset: some pharmacological effects (for example from bupropion) occur within hours and patients may notice appetite changes within 1–2 weeks, but clinically meaningful weight loss is typically evaluated over 12–16 weeks.
- Duration of action: the medicine is taken twice daily and therapeutic benefit is maintained only with continued treatment; clinical benefit should be reassessed periodically (initially at 16 weeks and then at least annually); long‑term safety beyond one year is not well established.
- Alcohol warning: avoid excessive alcohol and do not start Mysimba during acute alcohol or benzodiazepine withdrawal — alcohol and bupropion increase seizure risk and drinking may worsen side effects.
- The most common side effect is nausea; other frequent effects include constipation, headache, insomnia, dry mouth, dizziness and vomiting, and rare but serious risks include seizures and mood changes.
- Would you like to try Mysimba without a prescription?
Legal status and availability in the UK
In our online pharmacy, Mysimba is available without a prescription, with discreet delivery to the United Kingdom in 9–21 days.
Basic Mysimba information
- INN (international nonproprietary name): Naltrexone hydrochloride / Bupropion hydrochloride
- Brand names available in the United Kingdom: Mysimba (blister pack, 112 tablets)
- ATC code: A08AA62 — Antiobesity preparations, excl. diet products; naltrexone and bupropion combinations
- Forms and strengths: film-coated tablets 8 mg naltrexone hydrochloride / 90 mg bupropion hydrochloride (tablet contains 7.2 mg naltrexone and 78 mg bupropion on base)
- Manufacturers in the United Kingdom: Valeant (marketing as Mysimba)
- Registration status in the United Kingdom: Approved by the MHRA as Mysimba
- OTC / Rx classification: Prescription only (Rx)
Clinical effectiveness in the UK
Who benefits most from treatment in routine NHS care?
Mysimba is used as a second-line pharmacotherapy for adults who meet the BMI criteria and who have not achieved sufficient weight loss with diet and exercise.
Adherence and outcomes vary, with the largest benefits seen in patients who reach at least 5% weight loss by 16 weeks, consistent with the licensed stopping rule.
Early side effects such as nausea, insomnia and mood changes are frequent reasons for stopping treatment in real-world use.
In diabetes clinics, reductions in HbA1c have generally been modest and regular review of antidiabetic therapy is advised to manage hypoglycaemia risk where appropriate.
- Weight %: Greatest response seen in those achieving ≥5% by 16 weeks.
- Adherence: Variable; early side effects drive early discontinuation.
- Discontinuation reasons: Nausea, insomnia, mood changes, palpitations or blood pressure rise.
Indications and expanded uses — MHRA-approved and off-label practice
Who is eligible for treatment under the licence and where is off-label use seen?
- Licensed indication: Adjunct to a reduced-calorie diet and increased physical activity for adults with BMI ≥30 kg/m², or ≥27 kg/m² with at least one weight-related comorbidity.
- MHRA position: Licensed in the UK as Mysimba.
- Off-label use: Occasionally used in private clinics for selected patients with lower BMI or as part of multimodal programmes, but NHS prescribing generally adheres to the licensed indication and the 16-week stopping rule.
Prescribers should follow a simple checklist before starting treatment.
- Confirm BMI and presence of weight-related comorbidity for eligibility.
- Exclude absolute contraindications such as pregnancy, opioid dependence, seizure disorder or concomitant naltrexone/bupropion products.
- Discuss contraception with women of childbearing potential and ensure effective contraception if treatment proceeds.
- Baseline blood pressure and review of concomitant medications, including CNS-acting and CYP-interacting drugs.
Absolute contraindications include opiate dependence and pregnancy and combining Mysimba with other naltrexone/bupropion products is prohibited.
Composition and brand landscape — active substances, packaging and UK brands
What exactly is in each tablet and how is it sold in the UK?
| Item | Detail |
|---|---|
| INN | Naltrexone hydrochloride / Bupropion hydrochloride |
| Per tablet content | Naltrexone 8 mg; Bupropion 90 mg (tablet contains 7.2 mg naltrexone and 78 mg bupropion on base) |
| Packaging | Blister pack, 112 tablets (United Kingdom) |
| Manufacturer | Valeant (marketed as Mysimba in the United Kingdom) |
| ATC code | A08AA62 |
Contraindications and special precautions — high-risk groups and lifestyle restrictions
Who must not receive Mysimba and who needs careful monitoring?
- Absolute contraindications: Hypersensitivity, concurrent use of other naltrexone/bupropion products, uncontrolled hypertension, seizure disorder or history of seizures, CNS tumours, recent opioid use or dependence, acute alcohol or benzodiazepine withdrawal, current or history of bulimia or anorexia nervosa, severe hepatic impairment, end-stage renal failure, MAOI use within 14 days, pregnancy.
- Relative contraindications: Cardiovascular disease, controlled hypertension (needs monitoring), mild hepatic or renal impairment, elderly patients (caution >65 years; not recommended >75 years), diabetes (monitor for hypoglycaemia), use of CYP-interacting medicines.
Seizures are rare but serious and bupropion-containing products increase seizure risk, especially with abrupt alcohol or benzodiazepine withdrawal.
Monitor blood pressure at baseline and regularly thereafter, as increases in blood pressure have been reported.
Lifestyle advice includes avoiding initiation in patients with recent heavy alcohol use and counselling on driving if dizziness or insomnia occurs.
Dosage guidelines — NHS‑recommended regimens and special population adjustments
How is dosing started and adjusted safely in different patients?
| Week | Regimen |
|---|---|
| Week 1 | 1 tablet in the morning |
| Week 2 | 1 tablet morning, 1 tablet evening |
| Week 3 | 2 tablets morning, 1 tablet evening |
| Week 4 onward | 2 tablets morning, 2 tablets evening (maximum 4 tablets daily = 32 mg naltrexone / 360 mg bupropion) |
Start treatment with the recommended titration and reassess at 16 weeks and discontinue if the patient has not lost at least 5% of baseline body weight.
Renal impairment: contraindicated in end-stage renal failure; for moderate to severe impairment, do not exceed 2 tablets per day and use a slower titration starting at 1 tablet daily in week 1.
Hepatic impairment: contraindicated in severe hepatic impairment; for mild impairment begin at 1 tablet daily and titrate cautiously.
Not recommended in children and adolescents under 18 years.
Interactions overview — pharmacological, food/drink and MHRA reports
Which drugs and behaviours increase risk while taking Mysimba?
Bupropion increases seizure risk and this risk is amplified by other agents that lower the seizure threshold or by abrupt withdrawal from alcohol or benzodiazepines.
Avoid concomitant use with monoamine oxidase inhibitors and do not start if MAOI therapy has been used in the prior 14 days.
When combined with serotonergic medicines monitor for serotonin syndrome even though the risk is related to concomitant serotonergic agents rather than Mysimba alone.
Alcohol is a key interaction risk; advise patients to minimise heavy drinking and inform prescribers about recent withdrawal episodes.
- Major drug classes to avoid / monitor: Opioids, recent benzodiazepine or alcohol withdrawal, MAO inhibitors, other bupropion or naltrexone products, drugs that lower seizure threshold, CYP-interacting medicines.
Pharmacists should report suspected interactions and new adverse events via the MHRA Yellow Card system as part of routine vigilance.
Comparable medicines and prescribing preferences — NHS alternatives and pros/cons checklist
Which alternatives are commonly considered in NHS practice and how do they compare?
| Medicine | Efficacy | Route | Key risks |
|---|---|---|---|
| Orlistat | Modest weight loss | Oral | GI side effects, fat-soluble vitamin considerations |
| Liraglutide (Saxenda) | Greater average weight loss vs oral options | Injectable | GI upset, pancreatitis risk signals |
| Semaglutide (Wegovy) | High average weight loss in trials | Injectable | GI side effects |
| Mysimba | Oral; moderate weight loss vs placebo | Oral | Seizure risk, hypertension, neuropsychiatric effects |
- Clinician checklist: confirm BMI and comorbidity, prior pharmacotherapy, cardiovascular profile, mental health history, contraception and potential drug interactions before choosing therapy.
Mysimba advantages include oral dosing and a clear 16-week stopping rule; limitations include lower average weight reduction compared with some GLP‑1 agents and specific contraindications such as seizure risk.
Frequently asked questions
What do patients ask most about Mysimba?
- How long until I know if Mysimba works? — Assess at 16 weeks and discontinue if the patient has not lost at least 5% of baseline body weight.
- Can I take Mysimba with my diabetes drugs? — Often yes, but review hypoglycaemia risk and coordinate with the diabetes clinic for glucose monitoring and therapy adjustments.
- Is it safe if I drink alcohol? — Heavy drinking and recent alcohol or benzodiazepine withdrawal increase seizure risk; patients should minimise alcohol and report withdrawal history.
- How do I report side effects? — Use the MHRA Yellow Card scheme via the NHS app or the Yellow Card website and inform your GP or pharmacist.
Managing common side effects:
- For nausea: take with food and consider dose timing adjustments under clinician guidance.
- For insomnia: review timing of evening doses and advise sleep hygiene; consider dose adjustment if persistent.
- For palpitations or new hypertension: check blood pressure and stop treatment if uncontrolled.
Guidelines for proper use — UK pharmacist counselling style and NHS support portals
How should pharmacists counsel patients starting Mysimba in a way that supports safety and adherence?
Confirm indication and eligibility including BMI and comorbidity and review the full list of absolute contraindications before supply.
Explain the titration schedule week by week and make the 16-week evaluation and stopping rule clear at the first consultation.
Provide practical advice on managing common adverse effects such as taking with food to reduce nausea and recommending sleep hygiene to mitigate insomnia.
Advise patients to avoid heavy alcohol use and to report any history of seizures, head tumours, bulimia or recent opioid use.
Discuss drug interactions specifically MAOIs, opioids and medicines that lower the seizure threshold and document counselling in the patient record.
Storage advice: keep the tablets in the original packaging and store below 30°C, away from moisture and out of reach of children.
Signpost NHS resources such as the NHS App, GP online services, NHS 111, local weight-management referrals and psychological support services.
Encourage reporting of suspected adverse reactions to the Yellow Card scheme and provide simple written notes for patients to take away.
Delivery across the United Kingdom
| City | Region | Delivery time |
|---|---|---|
| London | England | 9–21 days |
| Birmingham | England | 9–21 days |
| Manchester | England | 9–21 days |
| Glasgow | Scotland | 9–21 days |
| Edinburgh | Scotland | 9–21 days |
| Leeds | England | 9–21 days |
| Liverpool | England | 9–21 days |
| Bristol | England | 9–21 days |
| Sheffield | England | 9–21 days |
| Newcastle | England | 9–21 days |
| Nottingham | England | 9–21 days |
| Leicester | England | 9–21 days |
| Cardiff | Wales | 9–21 days |
| Belfast | Northern Ireland | 9–21 days |
| Southampton | England | 9–21 days |
