Mysimba (Naltrexone/Bupropion)

What is Mysimba?

Mysimba is a prescription weight-management medicine containing two active ingredients: naltrexone and bupropion, in prolonged-release tablets. It is approved by the European Medicines Agency (EMA) for weight management in adults, used as an adjunct to a reduced-calorie diet and increased physical activity.

Mysimba is indicated for adults with an initial body mass index (BMI) of 30 or above (obese), or a BMI of 27 to below 30 (overweight) in the presence of one or more weight-related comorbidities, such as type 2 diabetes, dyslipidaemia, or controlled hypertension.

How does Mysimba work?

Mysimba combines two medicines that act on the central nervous system pathways regulating appetite and food reward:

• Naltrexone is an opioid receptor antagonist that contributes to effects on appetite and food reward; this is not an indication for binge-eating disorder.
• Bupropion is a norepinephrine-dopamine reuptake inhibitor. It increases the activity of these neurotransmitters in the hypothalamus, reducing hunger and supporting energy balance.

Together, these actions help reduce appetite and food cravings, making it easier to follow a reduced-calorie diet. Mysimba is not a stimulant and is not related to GLP-1 medicines such as semaglutide.

Who is Mysimba for?

Mysimba may be considered for adults aged 18 and over who have:

• A BMI of 30 or above, or
• A BMI of 27 or above with at least one weight-related condition such as type 2 diabetes, dyslipidaemia (high cholesterol), or controlled hypertension

Mysimba is not suitable for everyone. It must not be used by people who:

• Use opioid medicines or are dependent on opioids
• Are in acute opioid withdrawal or receive opioid-agonist treatment
• Take another medicine containing naltrexone or bupropion
• Have uncontrolled high blood pressure
• Have current or previous seizures
• Have a central nervous system tumour
• Are in acute withdrawal from alcohol, benzodiazepines, or other sedatives
• Have severe hepatic impairment or end-stage renal failure
• Have a history of bipolar disorder
• Are pregnant or breastfeeding
• Have taken an MAO inhibitor antidepressant in the last 14 days
• Have current or previous bulimia or anorexia
• Are allergic to any Mysimba ingredient

A full medical assessment by a qualified, independent doctor is required before any prescription can be issued.

Dosage

Mysimba is a daily oral tablet taken with food and swallowed whole. The dose increases gradually over four weeks to improve tolerability:

The maximum dose is 4 tablets per day, equivalent to 32 mg naltrexone hydrochloride and 360 mg bupropion hydrochloride. Each tablet contains 8 mg naltrexone hydrochloride (7.2 mg naltrexone base) and 90 mg bupropion hydrochloride (78 mg bupropion base). Moderate/severe renal impairment or mild hepatic impairment: maximum 2 tablets daily, one morning and one evening, after the initial week of one morning tablet. Moderate hepatic impairment: not recommended; severe hepatic impairment and end-stage renal failure: contraindicated. Use with caution over 65 years; not recommended over 75. Do not adjust your dose without consulting your prescribing doctor.

If at least 5% of starting body weight has not been lost after 16 weeks of treatment, the prescriber should discontinue Mysimba. At least once a year, a doctor must reassess benefit and cardiovascular risk. Because cardiovascular safety beyond 12 months remains uncertain, the prescriber should discontinue after one year if at least 5% weight loss from starting body weight has not been maintained.

Side effects

As with all medicines, Mysimba may cause side effects. Not everyone experiences them, and many become milder as the body adapts.

Very common side effects

• Nausea, constipation, vomiting and headache

Other reported effects

• Dry mouth, dizziness, insomnia and anxiety
• Increased blood pressure and heart rate

Consult the combination-product table in section 4.8; frequencies from either ingredient used alone cannot be transferred to Mysimba.

Taking Mysimba with food and following the gradual dose schedule helps reduce nausea. Blood pressure and heart rate should be monitored during treatment.

Serious side effects

• Seizures: Bupropion can lower the seizure threshold. Stop Mysimba, seek immediate medical attention if you experience a seizure, and do not restart.
• Hypertensive reactions: Report severe headache, vision changes, or chest pain to a doctor promptly.
• Mood changes: Bupropion carries a warning for depression and suicidal thoughts in some people. Contact a doctor immediately if you experience mood deterioration, agitation, or unusual thoughts.

Stop Mysimba and seek immediate medical attention for a serious allergic reaction or blistering/peeling skin rash. Do not restart after a serious skin reaction. Naltrexone can precipitate opioid withdrawal and block pain relief; follow the professional interruption plan below.

Other precautions and interactions

Measure blood pressure and pulse before treatment and regularly thereafter; sustained clinically relevant increases require discontinuation by the treating clinician. Discuss heart or cerebrovascular disease, Brugada syndrome or family history of sudden cardiac death, diabetes and all psychiatric history. Insulin or other diabetes medicines may need adjustment to avoid hypoglycaemia, which can increase seizure risk. Kidney function should be checked before treatment in people at increased risk, including older adults and people with diabetes.

Disclose every medicine, especially serotonergic antidepressants, medicines lowering the seizure threshold, tamoxifen and medicines affected by CYP2D6 or CYP2B6. Serotonin syndrome has been reported with serotonergic combinations, including opioids: agitation or confusion with fever, rapid pulse, rigidity or incoordination needs urgent assessment. Do not stop another prescribed medicine yourself. Minimise or avoid alcohol.

Stop Mysimba and contact the clinician for suspected liver injury, such as jaundice. Specified hereditary galactose intolerance, total lactase deficiency or glucose-galactose malabsorption preclude use. Avoid driving with dizziness, somnolence, loss of consciousness or seizures until resolved. Carry the patient card at all times, including for surgery or pain treatment; opioid sensitivity may increase after Mysimba is stopped.

Important safety and follow-up

Mysimba must not be used by people with allergy to its ingredients; uncontrolled hypertension; current or previous seizures; a central nervous system tumour; acute withdrawal from alcohol, benzodiazepines or other sedatives; a history of bipolar disorder; current treatment with another medicine containing bupropion or naltrexone; current or previous bulimia or anorexia; current opioid use, opioid dependence, opioid agonist treatment or acute opioid withdrawal; MAOI use within the last 14 days; pregnancy or breastfeeding; or severe hepatic impairment or end-stage renal failure.

Tell the independent doctor about every opioid-containing medicine, including pain, surgery, cough, cold or diarrhoea products. Naltrexone can precipitate withdrawal and block opioid pain relief. Tell the doctor and surgical team well before any planned surgery or possible need for opioid pain relief; the clinical team must plan interruption. For intermittent opioid treatment the label requires stopping Mysimba for at least 3 days beforehand; do not increase opioid doses to overcome blockade. After prior opioid use, the label requires at least 7–10 opioid-free days before considering Mysimba, with professional assessment. Do not start or interrupt treatment yourself except for an emergency stop instruction such as a seizure or serious allergic reaction.

At least once a year, a doctor must reassess the treatment benefit and cardiovascular risk. Cardiovascular safety beyond 12 months remains uncertain. The prescriber should discontinue after one year if at least 5% weight loss from starting body weight has not been maintained.

Mysimba vs other weight-management options

Which option is appropriate depends on your medical history, current medicines, and treatment goals. An independent doctor makes this decision during the assessment — Prescrivia does not influence or guarantee prescribing outcomes.

Online assessment for Mysimba (Naltrexone/Bupropion)

Mysimba is a prescription-only medicine in all EU member states. Prescrivia is a technology intermediary — we do not prescribe medicines, employ doctors, or sell medicines. Our platform connects patients with independent doctors:

1. Complete an online assessment: Answer questions about your height, weight, medical history, and current medicines.
2. Doctor review: An independent doctor reviews your assessment. If Mysimba is clinically appropriate, they may issue a prescription; if not, they will explain why and may suggest alternatives.
3. Pharmacy dispensing: Dispensing is the responsibility of licensed pharmacies under applicable national rules; this article does not establish stock or delivery. Prescrivia does not guarantee that a prescription will be issued.

In Spain, distance sale of prescription medicines is prohibited under Article 3.5 of Royal Legislative Decree 1/2015. An online assessment does not remove this restriction. Dispensing and access depend on the exact product and applicable national rules.

Sources

• EMA: current Mysimba product information, sections 2 and 4.1–4.8.
• EMA: amfepramone withdrawal decision.