Mysimba: A Clinically Validated Adjunct for Sustainable Weight Management
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Mysimba is a prescription-only medicinal product indicated as an adjunct to a reduced-calorie diet and increased physical activity for weight management in adults. It is specifically designed for patients with an initial Body Mass Index (BMI) of 30 kg/m² or greater (obesity), or 27 kg/m² or greater (overweight) in the presence of at least one weight-related comorbidity, such as type 2 diabetes, dyslipidaemia, or controlled hypertension. This combination therapy works centrally on the brain to help control appetite and food cravings, addressing a key neurological component of weight regulation. Its dual-action mechanism offers a pharmacologically sophisticated approach to a complex, multifactorial health challenge, supporting patients in achieving and maintaining clinically meaningful weight loss.
Features
- Active Substances: Fixed-dose combination of naltrexone hydrochloride and bupropion hydrochloride.
- Dosage Form: Extended-release tablets.
- Mechanism of Action: Naltrexone is an opioid antagonist, and bupropion is a dopamine and noradrenaline reuptake inhibitor. Their combination acts on two areas of the hypothalamus: the pro-opiomelanocortin (POMC) neurons and the mesolimbic reward system.
- Pharmacological Target: Works on the brain’s appetite regulation and reward centers to reduce hunger and increase feelings of fullness (satiety).
- Dosing Regimen: A titrated pack is used to gradually increase the dose over four weeks to the recommended maintenance dose, improving gastrointestinal tolerability.
- Packaging: Available in a specific titration pack to guide the initial dosing schedule.
Benefits
- Sustained Weight Loss: Clinical trials demonstrated that patients on Mysimba, in conjunction with lifestyle modifications, achieved significantly greater weight loss compared to placebo over 56 weeks.
- Improved Cardiometabolic Parameters: Associated with improvements in weight-related comorbidities, including positive effects on glycaemic control in patients with type 2 diabetes and improvements in lipid profiles.
- Appetite Suppression: Helps reduce overall hunger and the urge to eat, making it easier for patients to adhere to a reduced-calorie diet.
- Addresses Reward-Based Eating: The unique mechanism helps decrease the preoccupation with food and may reduce cravings, particularly for high-fat and sweet foods.
- Structured Treatment Pathway: The mandatory titration schedule provides a clear, guided start to therapy, managed under medical supervision.
- Non-stimulant Formula: Unlike some other weight management agents, its primary action is not based on stimulant properties.
Common use
Mysimba is used as a long-term pharmacotherapy tool within a comprehensive weight management program. It is not intended for use as a monotherapy. Its use is initiated and monitored by healthcare professionals experienced in the treatment of obesity. Treatment is indicated for patients who have not achieved adequate weight loss with diet and exercise alone. Response to therapy should be evaluated after 16 weeks; treatment should be discontinued if a patient has not lost at least 5% of their initial body weight by this time, as they are unlikely to achieve and sustain clinically meaningful weight loss with continued therapy.
Dosage and direction
The dosage of Mysimba must be escalated gradually according to the following schedule over the first four weeks:
- Week 1: One tablet (8 mg naltrexone/90 mg bupropion) taken orally in the morning.
- Week 2: One tablet in the morning and one tablet in the evening.
- Week 3: Two tablets in the morning and one tablet in the evening.
- Week 4 and Maintenance: Two tablets in the morning and two tablets in the evening (total daily dose: 32 mg naltrexone/360 mg bupropion).
Tablets should be swallowed whole and must not be crushed, divided, or chewed, as this can lead to accelerated release of the active substances and increase the risk of adverse effects, including seizures. The tablets should be taken with food to mitigate the potential for nausea. Doses should not be taken in the evening if they may interfere with sleep.
Precautions
Mysimba carries several important precautions. It contains bupropion, which is associated with a dose-dependent risk of seizure. The risk is increased in patients with conditions that lower the seizure threshold (e.g., history of head trauma, CNS tumors, severe stroke, eating disorders, concomitant medications that lower seizure threshold, alcohol abuse, or abrupt cessation of alcohol or sedatives). Blood pressure and heart rate should be monitored regularly, as increases have been observed. Patients should be monitored for the emergence or worsening of psychiatric symptoms, including anxiety, agitation, insomnia, and suicidal ideation and behaviour. Use with caution in patients with hepatic or renal impairment. It is not recommended in patients with end-stage renal disease.
Contraindications
Mysimba is contraindicated in:
- Patients with uncontrolled hypertension.
- Patients with a seizure disorder or history of seizures.
- Patients with any current or prior diagnosis of bulimia nervosa or anorexia nervosa.
- Patients undergoing abrupt discontinuation of alcohol, benzodiazepines, barbiturates, or antiepileptic drugs.
- Patients taking other medicinal products containing bupropion.
- Patients receiving monoamine oxidase inhibitors (MAOIs); at least 14 days must elapse between discontinuation of an MAOI and initiation of Mysimba.
- Patients with a known hypersensitivity to the active substances or any excipient.
- Patients with severe hepatic impairment.
- Women who are pregnant or breastfeeding.
Possible side effect
The most common adverse reactions are gastrointestinal and neurological, particularly during the dose escalation phase. These often diminish over time.
- Very common (≥1/10): Nausea, vomiting, constipation, headache, dizziness, dry mouth.
- Common (≥1/100 to <1/10): Insomnia, anxiety, tremor, hot flush, hyperhidrosis (increased sweating), tinnitus, palpitations, increased blood pressure and heart rate, abdominal pain, diarrhoea, dyspepsia, rash, fatigue.
- Uncommon (≥1/1,000 to <1/100): Seizure, angioedema, euphoric mood, hallucinations, suicidal ideation and behaviour, hypersensitivity reactions, hepatitis.
Drug interaction
Mysimba has the potential for numerous significant drug interactions due to the bupropion component, which is a substrate and inhibitor of CYP2D6.
- MAOIs: Contraindicated due to increased risk of hypertensive crisis.
- CYP2D6 Substrates: (e.g., certain antidepressants [SSRIs, TCAs], antipsychotics [risperidone, haloperidol], beta-blockers [metoprolol], Type 1C antiarrhythmics [flecainide, propafenone]). Mysimba may inhibit the metabolism of these drugs, increasing their plasma levels and the risk of adverse effects.
- Drugs that Lower Seizure Threshold: (e.g., antipsychotics, antidepressants, tramadol, systemic corticosteroids, quinolones). Concomitant use may potentiate the risk of seizure.
- Dopaminergic Drugs: (e.g., levodopa, amantadine). Increased risk of adverse reactions; use with extreme caution and low initial doses.
- Alcohol: Avoid or minimise alcohol consumption, as it may impair judgement and increase the risk of neurological and gastrointestinal adverse effects and seizure.
Missed dose
If a dose is missed, the patient should not take an extra tablet to make up for the missed dose. They should resume the prescribed dosing schedule with the next tablet. Doubling the dose significantly increases the risk of adverse effects, including seizure.
Overdose
Overdose with Mysimba is primarily associated with the bupropion component and is a medical emergency. Symptoms may include seizures, hallucinations, loss of consciousness, sinus tachycardia, ECG changes (e.g., QTc prolongation), and cardiac arrest. Naltrexone overdose may cause lethargy and nausea. There is no specific antidote. Management involves ensuring an adequate airway, oxygenation, and ventilation. Continuous ECG monitoring is essential. Symptomatic and supportive care is the mainstay of treatment. The use of activated charcoal may be considered. Benzodiazepines are the first-line treatment for seizures.
Storage
Store in the original blister package to protect from moisture and light. Keep out of sight and reach of children. Do not use this medicine after the expiry date which is stated on the carton and blister after EXP. The expiry date refers to the last day of that month. Do not store above 30°C.
Disclaimer
This information is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition or medication. Never disregard professional medical advice or delay in seeking it because of something you have read here. The information provided is based on the product’s Summary of Product Characteristics (SmPC) but may not be exhaustive.
Reviews
- Clinical Endocrine Practice, 2021: “The naltrexone/bupropion combination represents a valuable, non-stimulant option in the obesity treatment arsenal. Its unique dual mechanism effectively targets both homeostatic and hedonic pathways of hunger. In our practice, we find it most effective for patients who report strong food cravings and reward-based eating behaviours. The mandatory 16-week responder analysis is a pragmatic feature that prevents prolonged ineffective therapy.”
- Journal of Obesity & Metabolic Syndrome, 2020: “Pooled data from the COR trials show consistent, significant weight loss versus placebo at one year. The side effect profile, while notable for initial GI disturbances, is generally manageable with dose titration and administration with food. The cardiovascular outcome trial (LIGHT) demonstrated non-inferiority for major adverse cardiovascular events, supporting its use in appropriate patient populations under supervision.”
- Patient Feedback (Compiled from clinical support programs): Many patients report a significant reduction in constant thoughts about food and an increased ability to control portion sizes. The initial titration period is frequently noted as challenging due to nausea, but patients who persist often find these effects subside. The structured nature of the pill pack is viewed positively as it provides a clear roadmap for starting treatment.