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How Long Do Mysimba Side Effects Last?

Are you considering taking Mysimba as part of your Weight Loss? If so, one of the more common concerns people have is “How long do Mysimba effects last?”

This guide will help you to understand the duration of Mysimba side effects, what may increase the risk of getting them, and how to manage Mysimba side effects.

Understanding Side Effects of Mysimba

Mysimba side effects commonly include feeling sick (nausea), being sick (vomiting), constipation, headache, and tiredness. For a more detailed explanation of Mysimba side effects, check the patient information leaflet (PIL).

Duration of Mysimba Side Effects

Mysimba side effects are different for each person. We look at this in more detail below.

Some people get side effects after the first dose, while others may not get any until their Mysimba dosage increases.

Not everyone who takes Mysimba will get side effects.

Understanding the half-life of Mysimba can provide a deeper insight into this. Half-life refers to how long it takes for 50% of the medication to leave your body. Mysimba half-life is different for each active ingredient:

  • bupropion - 21 hours
  • naltrexone - 5 hours

This means Mysimba side effects should start to lessen as the medication leaves your body.

If you continue with treatment, you may get side effects for a few days to a few weeks.

Mysimba Side Effects Duration for Different Groups

Various factors can influence Mysimba side effects duration, such as:

  • pre-existing medical conditions
  • other medications
  • age

Missing Mysimba doses or taking too much can increase your risk of side effects.

If you take more Mysimba than you have been prescribed, speak to a doctor immediately or go to A&E.

Long-term Side Effects of Mysimba

Your doctor or prescriber will monitor your Mysimba side effects. You can stop taking it at any time, as long as you speak to them first.

Risks and Benefits of Long-term Use

Long-term Mysimba benefits include:

  • reaching weight loss goals, which can reduce the risk of long-term conditions like heart disease and lengthen life expectancy
  • decreased appetite
  • improved self-esteem and body confidence

Mysimba risks/potential long-term side effects include:

  • lupus
  • high blood pressure (hypertension)
  • a slightly increased risk of having a seizure (1 in 1000)
  • mental health problems, such as anxiety or depression

The best way to limit long-term side effects is to follow your prescriber’s instructions when taking Mysimba.

Managing Side Effects of Mysimba

You can manage Mysimba side effects as you usually would if you had these symptoms. For example:

  • headache can be treated with painkillers and rest
  • nausea and vomiting can be treated by eating little and often and avoiding large, fatty, spicy, or greasy meals

If you notice any of these side effects, it could be a sign of something more serious and requires immediate medical attention:

  • suicidal thoughts
  • loss of consciousness
  • red, itchy spots
  • severe muscle cramps
  • hallucinations
  • a sudden change in blood pressure

Additional guidance on managing the side effects of Mysimba can be found in the associated risk management plan


Duration of Mysimba side effects is unique to each person. You may be more likely to get Mysimba side effects if you overdose, have certain health conditions, or take certain medications. A healthcare professional will only ever prescribe Mysimba if they think it’s a safe and suitable weight loss treatment for you.

If you experience Mysimba side effects for a prolonged time, contact your doctor. You can also speak to one of our prescribers, learn more about Mysimba, or read about our other weight loss treatments.

Authored & Reviewed By

Mohamed Imran Lakhi

MPharm - Lead Pharmacist
Imran Lakhi is the superintendent pharmacist and founder at Prescription Doctor. He has been at the core of our team.

Published on: 23/10/2023 Reviewed on: 01/11/2023
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