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Mysimba is a weight-management tablet combining naltrexone and bupropion, which act together on the brain areas that control appetite and food reward. It has been authorised across the European Union since 26 March 2015, so a licensed doctor can prescribe it, and an EU pharmacy can dispense it, when clinically appropriate.

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What it is

Mysimba is licensed as an addition to a reduced-calorie diet and more physical activity, for adults with a BMI of 30 or above, or a BMI of 27 to 30 with a weight-related health problem. It is a tablet combining naltrexone and bupropion, which act together on the brain areas that control appetite and food reward, so hunger and cravings are reduced.

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How it works

Naltrexone and bupropion act together on the brain areas that control appetite and food reward. Bupropion inhibits reuptake of dopamine and noradrenaline, increasing firing of pro-opiomelanocortin (POMC) neurons in the hypothalamic arcuate nucleus. Naltrexone blocks the mu-opioid receptor on the same POMC neurons, preventing the auto-inhibitory feedback that would otherwise limit their activation. The combined effect is sustained POMC activation, which reduces food intake through melanocortin signalling and modulation of mesolimbic reward pathways. The relevant molecular targets are the mu-opioid receptor (blocked by naltrexone), the dopamine transporter and the noradrenaline transporter.

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What the studies reported

The pivotal trial is COR-I, published in The Lancet (PMID 20673995) and registered on ClinicalTrials.gov as NCT00532779. It was a phase 3, randomised, double-blind, placebo-controlled trial at 34 US sites. Of 1,742 enrolled adults (BMI 30–45 kg/m², or 27–45 with dyslipidaemia or hypertension), 583 received naltrexone 32 mg/day plus bupropion 360 mg/day, 578 received naltrexone 16 mg plus the same bupropion dose, and 581 received matching placebo — all for 56 weeks with a 3-week dose escalation. The coprimary endpoints were the percentage change in bodyweight and the proportion achieving 5% or more weight loss. Mean weight change was −6.1% (NB32), −5.0% (NB16) and −1.3% (placebo); 48%, 39% and 16% respectively achieved 5% or more weight loss (all P<0.0001 vs placebo). Half the randomised participants (50%) did not complete the 56-week trial, which makes the average figures harder to interpret. The EMA completed a review of Mysimba on 28 March 2025, following an Article 20 referral.
EU rules require Mysimba to be stopped after 16 weeks if you have not lost at least 5% of your starting weight.

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Who it is not suitable for

Mysimba is contraindicated where the medicine’s pharmacodynamics make it unsafe. Bupropion lowers the seizure threshold, so it is contraindicated in anyone with a current seizure disorder or a history of seizures, and in anyone abruptly withdrawing from alcohol, benzodiazepines, or barbiturates. Naltrexone blocks mu-opioid receptors, so it must not be taken alongside opioid medicines (it precipitates withdrawal) or by anyone who requires opioid analgesia. Uncontrolled hypertension is a contraindication because bupropion can raise blood pressure further.

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Other weight-management options a doctor may also consider

Semaglutide (Wegovy / Ozempic)

Weekly GLP-1 receptor agonist. A doctor may prescribe it if your BMI and history match the indications. Requires follow-up.

Tirzepatide (Mounjaro)

Dual GLP-1/GIP agonist. Assessed by the doctor based on comorbidities and BMI.

Liraglutide (Saxenda)

Daily GLP-1 agonist. Indicated in selected patients with elevated BMI after medical evaluation.

Orlistat 120mg

A fat-absorption inhibitor. A non-GLP-1 alternative a doctor may consider based on your history.

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Common questions

Mysimba is a tablet combining naltrexone and bupropion, which act together on the brain areas that control appetite and food reward. It is licensed as an addition to a reduced-calorie diet and more physical activity, for adults with a BMI of 30 or above, or a BMI of 27 to 30 with a weight-related health problem.
Mysimba is authorised in the EU and can be prescribed when it is clinically appropriate. However, at present Hi Doctor’s doctors review weight-loss cases and recommend the option that fits your history — they may consider semaglutide, tirzepatide or other EU-authorised alternatives.
The COR-I trial was published in The Lancet. All participants also followed a reduced-calorie diet and exercise programme, and a large proportion of people randomised did not complete the 56-week trial, which makes the average figures harder to interpret. The EMA completed a review of Mysimba on 28 March 2025, following an Article 20 referral.
Mysimba must not be taken by people with uncontrolled high blood pressure, a history of seizures, or who are taking opioid medicines.
EU rules require Mysimba to be stopped after 16 weeks if you have not lost at least 5% of your starting weight. The doctor reassesses treatment at that point.

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How Hi Doctor handles it

Our doctors review every weight-loss option and recommend what fits your history and goals. A licensed EU doctor reviews your case and, if eligible, issues an electronic prescription valid at any EU pharmacy under Directive 2011/24/EU. Mysimba is sold under the US brand name Contrave, which is not itself an EU-authorised product. See pricing for the consultation fee — medication is paid separately, at a pharmacy of your choice.

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Start a consultation

Weight-loss consultation

Answer the weight-loss questionnaire and a registered doctor reviews it. They decide whether treatment is appropriate, which one, and at what dose — and declining is a normal outcome. See what it costs and how the review works.
This page is reference information, not medical advice and not a prescription. Whether a medicine is appropriate for you is decided by a registered doctor after reviewing your consultation.