Mysimba (naltrexone/bupropion)

Mysimba is a prescription-only, weight-loss medicine, for adults over 18 years of age. It contains two active substances:

• naltrexone hydrochloride; and
• bupropion hydrochloride.

You have been prescribed Mysimba to help you manage your weight; together with a reduced calorie diet, and physical exercise.


Pharmacist - M.B.A. (Public Health) D.I.C.

Mysimba (naltrexone/bupropion)

Mysimba is approved for use in patients with an…

Garvan J. Lynch
MBA (Public Health)

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Mysimba is approved for use in patients with an initial body mass index of 30 or greater or those with a body mass index of 27 or greater if they have additional weight-related conditions like:

  • controlled high blood pressure (hypertension);
  • type 2 diabetes; or
  • high levels of lipid (fat) in the blood.

If you have been taking Mysimba for 16 weeks and have not lost at least 5 per cent of your initial body weight, your doctor may discontinue your prescription.

Your doctor may also recommend stopping treatment if there are concerns about:

  • increased blood pressure; or
  • side effects of this medicine; or
  • the safety of this medicine.

How does it work?

Mysimba is believed to reduce hunger and help control cravings by working on two areas of your brain. These areas are involved in controlling how much:

  • food you eat; and
  • energy you use.

How do you take Mysimba

At first you take one tablet once a day in the morning. The dose will be gradually escalated.

  • Week 1: one tablet once a day – in the morning.
  • Week 2: one tablet twice a day – one in the morning and one in the evening.
  • Week 3: three tablets every day – two in the morning and one in the evening.
  • Week 4: and onward: two tablets twice a day – two in the morning and two in the evening.

The maximum recommended daily dose of Mysimba is two tablets taken twice a day. You should take this medicine by mouth, and preferably with food.

What if you take too much?

If you take too many tablets, you may be more likely to have a fit (seizure) or other side effects.

• DO NOT DELAY, contact your doctor or your nearest hospital emergency department immediately.

What do you do if you miss a dose?

Skip the missed dose and take your next dose at the next usual time.

  • Do not take a double dose to make up for a forgotten dose.

When should you stop taking Mysimba?

You may need to take Mysimba for at least 16 weeks to have its full effect.

Do not stop taking Mysimba without talking to your doctor first.

When is Mysimba not suitable?

Mysimba is not suitable if you:

  • Are allergic to naltrexone or bupropion
  • Have abnormally high blood pressure or uncontrolled blood pressure
  • Have a condition that causes seizures
  • Have a brain tumour
  • Are usually a heavy drinker and you have just stopped drinking alcohol, or if you are going to stop while taking Mysimba
  • Have recently stopped taking sedatives or medicines to treat anxiety, or if you are
  • going to stop them while you are taking Mysimba
  • Have bipolar disorder
  • Are using any other medicines that contain bupropion or naltrexone
  • Have an eating disorder or have had one in the past
  • Are currently dependent on chronic opiates or opiate

You should stop taking Mysimba immediately and consult your doctor if you experience any symptoms of an allergic reaction after taking this medicine (swelling of the throat, tongue, lips or face; difficulty swallowing or breathing; dizziness; fever; rash; pain in the joints or in the muscles; itching or hives). Always take Mysimba exactly as your doctor has told you. Check with your doctor or pharmacist if you are not sure. 

Like many medications, Mysimba should not be prescribed for certain patients and may cause unpleasant side effects for other patients. It is also advisable to talk to your doctor or pharmacist before taking Mysimba if you:

  • Feel depressed, contemplate suicide, have a history of attempting suicide or any other mental health problems
  • Have had a serious head injury or head trauma
  • Regularly drink alcohol
  • Regularly use medicines to help you sleep (sedatives)
  • Are currently dependent on, or addicted to, cocaine or other stimulating products
  • Have diabetes for which you use insulin or oral medicines that may cause low sugar levels in your blood (hypoglycaemia)
  • Are taking medicines that may increase the risk of seizures

If you are taking any other medicines including any non-prescription medicines, supplements or herbal medicines, please tell your doctor before taking Mysimba.

Do not take Mysimba with the following

  • Monoamine oxidase inhibitors

These medicines are used to treat depression or Parkinson’s disease. They include:

  • phenelzine,
  • selegiline, and
  • rasagiline.

You must stop taking these medicines for at least 14 days before starting Mysimba.

  • Opiates and opiate-containing medicines

If you are taking Mysimba do not take opiates or opiate-containing medicines, which can include:

  • medicines to treat coughs and colds like mixtures containing dextromethorphan or codeine;
  • methadone – can be taken by people addicted to opiates;
  • pain medicines like morphine and codeine;
  • diarrhoea medicines like paregoric.

You must have stopped taking any opiate medicines at least seven to 10 days before starting Mysimba. Your doctor may carry out a blood test to make sure that your body has cleared these medicines before starting your treatment.
One of the two main ingredients in Mysimba, naltrexone, blocks the effects of opiates. If you take higher doses of opiates to overcome the effects of naltrexone, you may suffer from an acute opiate intoxication which may be life threatening.
After you stop treatment with Mysimba, you may be more sensitive to low doses of opiates.

Side effects

  • Feeling sick (nausea), being sick (vomiting)
  • Pain in the abdomen
  • Constipation
  • Headache
  • Difficulty sleeping (take your evening dose of medication earlier in the evening rather than later)
  • Anxiety, agitation
  • Joint and muscle pain

If the side effects do not go away after one month of treatment, it is important to discuss this with your doctor. Your doctor can help you find ways to manage side effects, or may recommend you stop taking Mysimba.

Tell your doctor about any side effect that bothers you or doesn’t go away. This includes any possible side effects not listed here.
For more information on Mysimba, please read the Patient Information Leaflet inside your package of Mysimba medication.

Like all medicines, Mysimba can cause side effects, although not everybody gets them. Seizures are rare and may affect up to 1 in 1,000 people taking Mysimba. If you have a seizure, you should stop taking Mysimba and consult your doctor immediately.

Benefits of Mysimba

When you start taking Mysimba, you may see improvements in wellbeing by week eight of treatment. In the trials, patients on Mysimba reported improvement in their self-esteem and were able to move more freely. Patients also felt less hungry and had a reduced desire or craving for food.

Clinical studies with Mysimba have been performed in more than 4,500 patients who were overweight or obese. In these studies, Mysimba in combination with a reduced calorie diet and physical exercise, had significant effects on weight.

Mysimba will not help you to lose weight overnight, it is recommended that you continue treatment with Mysimba beyond 16 weeks if you have lost 5% or more of your body weight at week 16.

11.7%  weight loss was the average weight loss in people who continued treatment with Mysimba for one year.

32%  of these people lost over 15% of their body weight at one year.

Remember, if you have been taking Mysimba for 16 weeks and have not lost at least 5% of your initial body weight, your doctor may discontinue your prescription. Please do not be discouraged if this happens, Mysimba may not work for you but there are other approaches you can take in consultation with your doctor.

As you start to lose weight, it is important to continue making healthy lifestyle choices and continue taking Mysimba, which may help you maintain your weight loss.





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