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Mysimba vs Saxenda: What's the Difference

Pharmacy2U Team | minute read
weightloss image, 2 women outside excising

If you’re exploring the different types of weight loss medications available on the market, you could become overwhelmed by the range of medical names but have no clear understanding of what these treatments actually mean for your body. To help you stay informed on your weight loss journey, this blog dives into the differences between two prominent weight loss treatments Saxenda and Mysimba, unpacking their mechanisms of action, side effects, and suitability.

FeatureMysimba (naltrexone/bupropion)Saxenda (liraglutide)
Mechanism of ActionAffects brain's reward system, reducing cravingsMimics natural gut hormone GLP-1, impacting digestion, insulin production, and appetite
Dosage and AdministrationTablets, gradually increasing dosage over the first monthPre-filled pen, daily injections gradually increasing dosage over the first month
Common Side EffectsNausea, constipation, diarrhoea, dry mouth, headache, difficulty sleepingNausea, constipation, diarrhoea, injection site reactions
Suitability ConsiderationsMay not be suitable for uncontrolled high blood pressure or a history of seizuresMay not be suitable if has severe gut or stomach issues, or bowel disease.

What is Mysimba?

Mysimba is a prescription weight loss treatment provided in the form of pills. These pills combine two established medications: naltrexone and bupropion. Both drugs work in different ways, but ultimately reduce cravings and appetite to help you on your weight loss journey.

What is Saxenda?

Saxenda is an injectable medication that contains liraglutide, a glucagon-like peptide-1 (GLP-1) receptor agonist. This works to induce feelings of fullness and slow down digestion, ultimately assisting you to lose weight.

Who is suitable for Mysimba and Saxenda?

For both Mysimba and Saxenda, the medications will only be prescribed for adults who are:

  • Classed as ‘obese’ with a BMI of 30 or over

  • Classed as ‘overweight’ but have a condition made worse by weight gain e.g., a heart condition

It is worth noting that both Mysimba and Saxenda work best when combined with a healthy calorie-restricted diet and regular exercise.

What are the differences between Mysimba and Saxenda?

As discussed earlier, Mysimba and Saxenda have different active ingredients. We’ll go through what this could mean for patients using the treatment, as well as any other differences between taking the two.

Biological effects on the body

Mysimba contains two active ingredients naltrexone and bupropion. Naltrexone is thought to impact the brain’s reward system, specifically for areas associated with pleasure and motivation which can reduce cravings. Bupropion is an antidepressant that can further influence feelings of fullness and satisfaction. These ingredients work in collaboration to make you feel more satiated and less likely to crave food or overeat. 

Saxenda, on the other hand, targets the gut rather than the brain. This medication contains liraglutide, a GLP-1 receptor agonist. GLP-1 is a natural hormone produced in the gut that plays a role in regulating appetite, blood sugar control, and digestion. Saxenda works by mimicking the effects of GLP-1 which leads to slowed digestion, increased insulin production, and appetite reduction.

Dosage and administration

Mysimba is prescribed in pill form and is slowly introduced to ensure your body adjusts well. Commonly the routine will look like this:

Week 1: One tablet, once in the morning

Week 2: One tablet in the morning and one in the evening

Week 3: Two tablets in the morning and one in the evening

Week 4 and onwards: Two tablets, twice daily

Saxenda is usually self-administered through a daily injection. When you are prescribed Saxenda, you will receive a pre-filled pen which can be injected either in the upper arm, front of the thigh, or the top of the waist. You will be given detailed instructions on how to use your injection pen, but speak to your doctor if you have any queries or worries.

Side effects

Both Mysimba and Saxenda can cause side effects, but they tend to differ in type and frequency. Here's a breakdown:

Mysimba (naltrexone/bupropion):

More Common:

  • Gastrointestinal issues: nausea, constipation, diarrhoea, vomiting

  • Dry mouth

  • Headache

  • Difficulty sleeping (insomnia)

Less Common:

  • Dizziness

  • Increased sweating

  • Anxiety

  • Changes in taste

Saxenda (liraglutide):

More Common:

  • Gastrointestinal issues: nausea, constipation, diarrhoea, vomiting

  • Injection site reactions: pain, redness, swelling

Less Common:

  • Dizziness

  • Headache

  • Fatigue

  • Low blood sugar (hypoglycemia)

As we can see, both medications can cause digestive issues. Mysimba may cause more central nervous system side effects like headaches, insomnia, and changes in taste. Saxenda might lead to low blood sugar, especially if combined with other medications for diabetes.

Studies find that side effects often lessen over time as your body adjusts to the medication. It's important to report any persistent or concerning side effects to your doctor or pharmacist.


There are certain stipulations for taking each of the medications, wherein certain individuals are not suitable for the treatment. This differs between the two, as each drug works on a different part of the body in different ways. 

There are circumstances where you shouldn’t take Mysimba, a full list can be found on our Mysimba page. Some main factors include if you have:

  • An allergy to either naltrexone or bupropion

  • Abnormally high blood pressure that is not under control by medication

  • Are pregnant or breastfeeding

  • A history of seizures

  • Bipolar disorder

  • Severe liver or kidney disease

  • A brain tumour

Saxenda, comparatively, is not recommended for individuals who:

  • Have an allergy to liraglutide

  • Have severe heart failure

  • Are pregnant or breastfeeding

  • Have a liver or kidney condition

  • Have severe stomach or gut issues that result in slow stomach emptying

  • Have inflammatory bowel disease

When you go through your consultation, your pharmacist will make sure to identify whether you are suitable for either of the treatments based on your current and historical health.

How to Buy Mysimba or Saxenda

Both medications are prescription only, meaning a healthcare professional will determine whether you are suitable for the treatment. At Pharmacy2U, we offer a simple online consultation with our doctors where you can get tailored results for weight loss treatments. If our doctors prescribe a weight loss medicine for you, we will write to your NHS GP to inform them, so they have a complete record of your treatment.