Mysimba (Bupropion Hydrochloride, Naltrexone Hydrochloride)

Mysimba acts on appetite regulation and energy balance pathways to support weight reduction in eligible adults.

• Obesity (BMI ≥30 kg/m²): supports weight loss when combined with diet and exercise.
• Overweight with comorbidity (BMI ≥27 kg/m²): aids weight reduction in patients with hypertension, type 2 diabetes, or dyslipidaemia.
• Weight‑management adjunct: improves metabolic parameters such as blood glucose and lipid profiles when used with lifestyle changes.

• Mysimba combines bupropion, a norepinephrine‑dopamine reuptake inhibitor, with naltrexone, an opioid‑receptor antagonist. Bupropion stimulates pro‑opiomelanocortin neurons in the hypothalamus, enhancing anorexigenic signaling, while naltrexone blocks feedback inhibition of these neurons, sustaining the effect. The synergistic action reduces appetite and increases energy expenditure, facilitating weight loss in conjunction with diet and exercise. This dual mechanism targets central pathways that govern reward and satiety, providing a pharmacologic complement to behavioral interventions.

Mysimba may cause a range of adverse reactions, which are categorized by frequency and severity.

Common Side Effects

• Nausea: mild to moderate stomach upset that often occurs early in treatment.
• Headache: transient cranial pain that may resolve without intervention.
• Constipation: reduced bowel movements leading to abdominal discomfort.
• Dry mouth: decreased salivation causing a feeling of thirst.
• Insomnia: difficulty falling or staying asleep, reported by some patients.

Serious or Rare Side Effects

• Seizures: potential convulsive episodes, particularly at higher doses or in predisposed individuals.
• Suicidal thoughts: emergence of depressive ideation or behavior requiring immediate evaluation.
• Severe allergic reaction: rash, swelling, or anaphylaxis that may need emergency care.
• Elevated blood pressure: significant rise in systolic or diastolic pressure requiring monitoring.

When prescribing Mysimba, clinicians should consider several precautionary measures to ensure safe use.

• Cardiovascular assessment: evaluate blood pressure and heart disease before initiating therapy.
• Seizure risk: avoid use in patients with a history of seizures or eating disorders.
• Psychiatric monitoring: watch for mood changes, depression, or suicidal ideation.
• Drug interactions: review concomitant medications that lower seizure threshold or affect neurotransmitters.
• Pregnancy and lactation: use only if potential benefit justifies potential risk, as safety data are limited.
• Store at ambient temperature: keep tablets below 25 °C in the original packaging, protected from moisture.

Mysimba can interact with other medicines, altering its efficacy or safety profile.

Major Interactions (Avoid)

• Monoamine oxidase inhibitors (MAOIs): risk of hypertensive crisis when combined with bupropion.
• Other opioid antagonists: may reduce the therapeutic effect of naltrexone.
• Seizure‑lowering drugs: concurrent use can increase seizure risk.

Moderate Interactions (Monitor Closely)

• CYP2B6 inhibitors (e.g., clopidogrel): may raise bupropion plasma levels.
• CYP3A4 inducers (e.g., rifampin): may decrease naltrexone concentrations.
• Antidepressants affecting serotonin: monitor for additive central nervous system effects.