Mysimba Guide: Naltrexone-Bupropion Dosing and Risks

Not everyone wants, or can use, an injection. If you are looking for an oral option, you may have come across Mysimba, known as Contrave in the United States and Canada. Mysimba is a prolonged-release tablet that combines two older medicines, naltrexone and bupropion, to reduce appetite and cravings. It is approved in the European Union and the United Kingdom for weight management alongside a reduced-calorie diet and increased physical activity. This 2026 guide explains how Mysimba works, who it suits, the dosing schedule, side effects, who should avoid it and how it compares with injections such as Wegovy and Mounjaro.

You can view the product on the Mysimba product page. As with all prescription medicines, treatment begins with a medical assessment, and this article is not a substitute for your prescriber’s advice or the patient leaflet.

In This Guide

• What Is Mysimba and How Does It Work?
• Who Is Mysimba For?
• How Much Weight Can You Lose With Mysimba?
• Mysimba Dosing Schedule
• Common Side Effects
• Serious Risks and Who Should Not Take Mysimba
• Mysimba vs Injections vs Orlistat
• Practical Tips for Taking Mysimba
• Cost and Availability
• Is Mysimba Right for You?

What Is Mysimba and How Does It Work?

Mysimba contains naltrexone hydrochloride 8 mg and bupropion hydrochloride 90 mg in each prolonged-release tablet. The two ingredients act on different parts of the brain.

• Bupropion is an antidepressant and smoking cessation aid that stimulates pro-opiomelanocortin (POMC) neurons in the hypothalamus, which reduces appetite and increases energy expenditure.
• Naltrexone is an opioid receptor blocker used in addiction treatment. It blocks an inhibitory feedback loop on POMC neurons, which prolongs the appetite-suppressing effect and may reduce food cravings and the rewarding aspects of eating.

The combined effect reduces hunger, cravings and reward-driven eating. It does not work through GLP-1 pathways, so it differs from semaglutide and tirzepatide. To learn about the injection mechanism, read how GLP-1 injections work.

Who Is Mysimba For?

In the EU and UK, Mysimba is indicated, alongside diet and exercise, for adults with a BMI of 30 or above (obesity), or a BMI of 27 to under 30 (overweight) with one or more weight-related conditions such as type 2 diabetes, dyslipidaemia or controlled hypertension. People who notice strong food cravings, emotional eating or reward-driven snacking sometimes do well with it, though a prescriber must make the decision. Some people choose Mysimba because they prefer tablets, because injections are unsuitable, or because of cost or supply issues.

How Much Weight Can You Lose With Mysimba?

Pivotal trials of naltrexone-bupropion found average weight loss of roughly 5 to 6 percent of body weight at one year, compared with around 1 to 2 percent on placebo, with some patients losing 10 percent or more. In comparison, semaglutide 2.4 mg produced about 15 percent loss over 68 weeks in STEP 1, and tirzepatide produced roughly 15 to 21 percent over 72 weeks in SURMOUNT-1. Mysimba therefore produces smaller average loss, but individual response varies, and some patients respond very well. Compare more options in our trial data review.

Mysimba Dosing Schedule

Mysimba is started slowly over four weeks to reduce side effects.

Week	Morning dose	Evening dose	Total daily tablets
Week 1	1 tablet	None	1
Week 2	1 tablet	1 tablet	2
Week 3	2 tablets	1 tablet	3
Week 4 onward	2 tablets	2 tablets	4

The maintenance dose is two tablets twice a day, with a maximum of four tablets daily. Swallow tablets whole and do not take them with high-fat meals, which can increase blood levels and the risk of seizures. Your prescriber reviews progress after 16 weeks on the maintenance dose. If you have not lost at least 5 percent of your starting weight, treatment should usually be stopped because continued benefit is unlikely.

Common Side Effects

• Nausea, constipation and vomiting, especially in the first weeks.
• Headache and dizziness.
• Dry mouth and altered taste.
• Trouble sleeping (insomnia) and anxiety.
• Increased heart rate and blood pressure.
• Irritability or tremor in some people.

Many side effects ease after the first few weeks. Taking tablets earlier in the day can reduce insomnia, and increasing water and fibre helps constipation. If you feel unwell, speak to your prescriber rather than stopping abruptly.

Serious Risks and Who Should Not Take Mysimba

Bupropion lowers the seizure threshold, so Mysimba is not suitable for people with a seizure disorder or conditions that increase seizure risk. It is also contraindicated in people with uncontrolled hypertension, those using opioid medicines or recovering from opioid dependence (because naltrexone blocks opioids), anyone with an eating disorder such as bulimia or anorexia, people undergoing abrupt alcohol or benzodiazepine withdrawal, those with severe liver or kidney impairment, and pregnant women. It should not be combined with monoamine oxidase inhibitors (MAOIs).

The product carries warnings about suicidal thoughts and behaviour, particularly in younger adults, because bupropion is an antidepressant. Anyone who notices new or worsening mood changes should seek help immediately. Interaction checks are essential: Mysimba is affected by medicines that influence CYP2D6, and it can alter levels of certain antidepressants, antipsychotics, beta blockers and heart rhythm medicines. See the broader safety checklist in who should not take weight loss medicines, and note that the exclusions differ from GLP-1 injections.

Mysimba vs Injections vs Orlistat

Feature	Mysimba	GLP-1 injections	Orlistat
Form	Daily tablets	Weekly injection	Capsules with meals
Mechanism	Appetite and craving control in brain	Appetite and glucose via GLP-1 (and GIP)	Blocks fat absorption in gut
Average weight loss in trials	About 5 to 6%	About 15% or more	About 3 to 4%
Main side effects	Nausea, insomnia, headache, blood pressure rise	Nausea, vomiting, constipation, diarrhoea	Oily stools, urgency, gas
Key restriction	Seizures, opioids, uncontrolled hypertension	MTC/MEN 2, pregnancy	Cholestasis, malabsorption

For the orlistat options, read Orlistat vs Xenical vs Alli. If you want to understand the differences between injection brands, see Mounjaro vs Wegovy.

Practical Tips for Taking Mysimba

1. Follow the titration table exactly. Do not skip steps to speed up results.
2. Take tablets with water and avoid crushing or chewing them.
3. Avoid high-fat meals when taking tablets.
4. Take the second daily dose early enough to avoid insomnia, usually with the evening meal.
5. Check your blood pressure and heart rate as advised.
6. Pair the medicine with protein-rich meals and exercise, as in our nutrition guide.
7. Book your 16-week review and be honest about results.

Cost and Availability

Availability and price depend on the country and whether you are buying privately. In many places, Mysimba is not funded by public systems for obesity. Compare provider fees, consultation costs and the monthly price of tablets, and read how much weight loss injections cost for a framework that also applies to oral medicines. Always buy from a licensed pharmacy.

Is Mysimba Right for You?

The right choice depends on your medical history, goals and preferences. Mysimba can be a sensible option if you cannot use injections, want to address cravings, or have not responded to lifestyle changes alone. Injections often deliver larger average weight loss, so if your health risk is high, your prescriber may favour them. A consultation will help; see what to expect in an online weight loss consultation, and for general medicine information, visit the NHS medicines pages. If you have questions, contact our team.

Who Tends to Respond Best to Naltrexone-Bupropion?

Responders often report that cravings and the mental pull toward snacks fall in the first weeks, even though the scale may lag behind. Studies suggest early weight loss predicts long-term success: people who lose at least 5 percent by week 16 are much more likely to reach 10 percent or more at one year. People who struggle with emotional eating, evening snacking or nicotine cravings sometimes find the tablets helpful, and because bupropion is also used for smoking cessation, those who are trying to quit smoking and manage weight may find a combined benefit, although this should be planned with a prescriber. Others find the side effects, especially nausea and insomnia, hard to tolerate, which is why gradual titration and early follow-up matter.

Monitoring While You Take This Medicine

A prescriber should check your blood pressure and heart rate before you start and regularly during treatment, particularly in the first three months. Report palpitations, chest pain, severe headaches or visual disturbances at once. Tell your doctor about all medicines and supplements, including over-the-counter cough and cold remedies, because some combinations increase seizure risk. Alcohol should be limited, as heavy drinking or sudden cessation raises the risk of seizures. Mood should be monitored, and family members can be encouraged to tell you or your clinician if they notice changes. Stop the tablets and seek urgent care if you have a seizure, an allergic reaction or severe mood changes.

Combining Tablets With Lifestyle Changes

Tablets work best as part of a programme. Aim for a modest calorie deficit, protein at each meal, vegetables and fibre, and regular movement that includes strength training. Sleep is vital because insomnia is a known side effect and poor sleep drives hunger. Track weight weekly, and plan non-scale measures such as waist, fitness and energy. If you reach a plateau, read our plateau guide, whose principles apply to any weight loss medicine, and discuss next steps with your prescriber if progress stalls.

Key Takeaways on Tablets

Naltrexone-bupropion is a prescription tablet for appetite and craving control that delivers more modest average weight loss than injections. Titrate slowly, monitor blood pressure and mood, avoid it if you have seizures or take opioids, and review progress at 16 weeks. Pair it with nutrition and exercise for the best results.

Editorial Standards and Sources

This guide was prepared by the Weight Lose Solution clinical content team. Medicine information is checked against official product labels and published trial data, and we update articles when guidance changes. It is educational only: prescription treatments are dispensed after an online assessment and approval by a licensed physician, and your own prescriber always takes priority.

Key sources used across our guides:

• Wilding JPH et al. Once-weekly semaglutide in adults with overweight or obesity (STEP 1). New England Journal of Medicine, 2021.
• Jastreboff AM et al. Tirzepatide once weekly for the treatment of obesity (SURMOUNT-1). New England Journal of Medicine, 2022.
• U.S. Food and Drug Administration drug information and approved product labelling.
• World Health Organization obesity and overweight fact sheet.

Related Guides and Next Steps

Continue your research with these related guides from our clinical content team:

• Buying weight loss injections in Canada
• Travelling with weight loss pens
• The difference between Ozempic and Wegovy
• GLP-1 and hair loss
• Buy weight loss injections online safely in the USA
• Wegovy side effects
• Mounjaro side effects
• Browse prescription weight loss medications

Frequently Asked Questions About Mysimba

Medical disclaimer: this article is for general education and is not medical advice. Prescription treatments are dispensed only after an online health assessment and approval by a licensed physician. Always follow the guidance of your own prescriber and the patient information leaflet.