What is Mysimba? How it works and side effects

Image of a knife, fork and measuring tape on a plate
Mysimba tablets are a weight loss treatment that reduces appetite and food cravings. This treatment is to be used alongside a healthy diet and exercise and is suitable for adults with a body mass index (BMI) of 30 or over. Over time, Mysimba can make you feel less hungry and prevent excessive weight gain. 
If diet and exercise alone have not helped you lose weight, there are weight-loss medications available to aid your weight-loss journey and help you reach your goals. Mysimba is one treatment that has proved successful in helping some people reduce their weight. If you’re considering buying Mysimba, here’s what to expect including how it works and the side effects you may experience. 

What is Mysimba used for? 

Mysimba is used for weight management by those who are having difficulty losing weight with just diet and exercise alone. However, not everyone can take Mysimba and you must meet certain criteria to be eligible for this weight loss treatment. 

Is Mysimba right for you? 

This medication is suitable for adults who are considered obese, which means your body mass index must be 30 or above. Alternatively, if you’re not technically obese but you are overweight with a BMI of 27-30, and you have health complications associated with being overweight such as heart disease or type 2 diabetes, then Mysimba should be suitable for you.
Mysimba is a good option if you have a healthy diet and are exercising regularly, but maybe this isn’t enough to reduce your weight without the help of a weight loss aid.  

How Mysimba works 

Woman looking at a plate of burger and chips and a bowl of salad
Mysimba contains two active ingredients known as naltrexone and bupropion. Unlike many other weight loss pills that work on the digestive system to prevent the body from absorbing fat, the ingredients in Mysimba work on areas of the brain to reduce appetite and curb food cravings. 
This can help prevent eating excessively or eating unhealthy foods, and eventually, this calorie-controlled diet can lead to a reduction in weight. 

Naltrexone and bupropion

Separately, these drugs have their own uses. When taken alone, naltrexone hydrochloride is used as a therapy to treat addictions, specifically opioid addiction by controlling the feeling of euphoria after taking these drugs. 
Similarly, bupropion hydrochloride is indicated for use in addictions to nicotine. When used with other therapies, this medicine can help people stop smoking. It may also be used to treat depressive disorders such as SAD (seasonal affective disorder)
When these drugs are combined, they have an effect on weight and eating habits, a positive effect on those who are overweight and struggling to lose it. 
The way naltrexone and bupropion work to control eating habits is yet to be fully understood, but we do know that they affect the parts of the brain that control pleasure (we often experience pleasure when eating high-fat and sugary foods), and also food intake and energy balance. Reducing pleasure associated with eating unhealthy foods and controlling excessive food intake combined with exercise, has proved successful in reducing weight in those who are obese or overweight. 

How much weight you could lose

Weight loss won’t happen overnight, it is a gradual process to help you manage your weight in a healthy and sustainable way. In a randomised study of over 4,500 participants, it was found that those taking Mysimba lost up to 5% of their body weight by week 16, and those that continued to 56 weeks lost over 8% of their body weight. 
It’s important to note that in this study, participants made lifestyle changes alongside taking Mysimba which had a positive effect on weight loss. 
After 16 weeks of taking Mysimba, you will be evaluated and if you haven’t lost at least 5% of your baseline body weight, treatment is usually stopped. 
Person stepping on weighing scales

How to take Mysimba

Mysimba comes in tablet form and should be taken orally with water. With Mysimba, the dose gradually increases week by week until 16 weeks when you will be evaluated to see if it is having the right effect on you. 
This gradual increase in dose can also help manage potential side effects that can happen when starting a new medication. 
In the first week, you will begin by taking 1 tablet per day in the morning, followed by 2 tablets per day in week 2 - 1 in the morning and 1 in the evening. In week 3 you will take 3 tablets per day, 2 in the morning and 1 in the evening, and in week 4 this increases to 4 tablets per day - 2 in the morning and 2 in the evening. From week 4 onwards it’s quite straightforward, continue taking 2 tablets in the morning and 2 in the evening each day until you reach week 16. 
Following this schedule is important but if you miss a dose, don’t worry! Taking more than the recommended dose can do more harm than good, so if you do forget a dose then you should skip this and take your next dose at your usual time.
If you’re considering taking Mysimba be sure that you are suitable first. There are certain medications that you may already take or conditions that you may have that could make you unsuitable for this type of treatment or increase the risk of side effects. For example, if you’re taking any medicines to treat high blood pressure or depression your doctor will need to monitor you closely to prevent serious side effects from occurring. 

Mysimba side effects

Side effects are a risk with any medicine. It’s important to remember that not everyone who takes Mysimba experiences side effects, but you should be aware of them. 
The most common side effects of Mysimba are headaches, constipation, nausea and vomiting. There are things you can do to help ease these side effects, but if they are becoming too difficult to deal with you should consult your doctor and consider stopping treatment. 
As always, a full list of side effects can be found on the patient information leaflet that comes with the medicine. The biggest risks associated with Mysimba are seizures in those who already have a condition that causes this. Mysimba is a prescribed medication, so you should always tell your doctor or our prescribers of any condition you have or medication you’re taking, and you will never be prescribed Mysimba if there is any risk to your health. 

How much does it cost?

Although Mysimba is approved in Europe, the only way to obtain this medication in the UK is to buy it privately. No matter where you buy it from you should always be asked a series of questions so that the prescriber can get a good understanding of your health and can determine if you’re suitable for this treatment. 
Whilst it’s not available for free on the NHS currently, prices start from £109.99 for a pack of 112 tablets at Chemist4U which takes you up to around week 7 of the treatment plan. The price includes your all-important consultation with one of our prescribers, your prescription, and the delivery of your medicine. 

Find out more about how to fund your weight loss treatment when it’s not available on the NHS, here

Laura Shillcock - Medical Content Writer
James O'Loan - CEO & Superintendent Pharmacist
James O'Loan , CEO & Superintendent Pharmacist on 19 October 2022
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