Direct answer
Is Mysimba dangerous?
Mysimba is not a medicine to take without a clinical assessment. It carries serious contraindications — particularly for people with a history of seizures, eating disorders, or current opioid use — and those people must not take it. For people who are properly screened and have none of the contraindications, the risk profile is manageable and consistent with other licensed prescription medicines. The key is screening: this is why Mysimba requires a prescription and a clinical review.
Common side effects
What most people experience
The following figures come from the Summary of Product Characteristics (SmPC), based on pooled Phase 3 trial data.
| Side effect | Frequency in trials | Notes |
|---|---|---|
| Nausea | 31.8% | Very common; most pronounced in weeks 1–4 and usually improves |
| Constipation | 18.1% | Common; staying hydrated and maintaining fibre intake can help |
| Vomiting | 9.9% | Common; often linked to nausea in the early titration period |
| Headache | Common | Reported more frequently during dose titration |
| Insomnia or disturbed sleep | Common | Bupropion has stimulant properties; avoid taking evening dose too late |
| Dry mouth | Common | Typically mild |
| Dizziness | Common | Particularly during the first weeks of treatment |
Why nausea is so common
Understanding early nausea on Mysimba
Nausea affects nearly one in three people in the trials. It happens because bupropion stimulates dopaminergic pathways connected to both appetite regulation and nausea. The slow four-week titration schedule is specifically designed to reduce this — starting at one tablet and building up gradually. For most people, nausea is at its worst in weeks one to three and settles once the maintenance dose is established. Taking tablets with food can also help.
Rare but serious
Rare serious effects to be aware of
Seizures (reported rate: ~0.06%)
Bupropion lowers the seizure threshold in a dose-dependent way. The rate in clinical trials was approximately 0.06% — around 1 in 1,700 people. Anyone with a history of seizures or epilepsy must not take Mysimba. If a seizure occurs, stop the medication immediately and seek emergency care.
Hypertensive episodes
Blood pressure and heart rate can increase, particularly during the first weeks of treatment. Blood pressure must be adequately controlled before starting Mysimba and should be monitored during treatment. Severe headache, chest pain, or sudden blurred vision warrant urgent medical assessment.
Absolute contraindications
Who must not take Mysimba
Also not recommended during pregnancy, breastfeeding, in people under 18, or in people over 75.
Interactions and cautions
Medicines that interact with Mysimba
Medicines that increase seizure risk
Antipsychotics, certain antidepressants (particularly tricyclics and SSRIs at higher doses), tramadol, theophylline, systemic corticosteroids, and some antimalarials can all lower the seizure threshold and increase risk when combined with bupropion.
Opioid medications
Naltrexone blocks opioid receptors. Taking Mysimba with any opioid painkiller — including codeine, tramadol, morphine, or opioid substitution therapy — will block the opioid’s effect and can trigger withdrawal symptoms in dependent individuals.
CYP2D6-metabolised medicines
Bupropion inhibits CYP2D6, an enzyme that metabolises some antidepressants, antipsychotics, and beta-blockers. Dose adjustments of co-prescribed medicines may be needed. Disclose all medications to your prescriber.
Dopaminergic medicines
Levodopa and amantadine (used in Parkinson’s disease) can interact with bupropion and increase the risk of side effects including nausea and psychiatric symptoms.
Before you start
What to tell your prescriber
All current medications
Including OTC medicines, supplements, and occasional-use drugs. Codeine in cough preparations is an opioid and is relevant.
Any history of seizures
Even a single seizure many years ago, or past anti-epileptic medication — this is relevant information that must be disclosed.
Any history of eating disorders
Past as well as current. Mysimba is contraindicated in people with a history of anorexia or bulimia regardless of current status.
Mental health history
Particularly bipolar disorder, psychosis, or significant depression. Bupropion has psychiatric effects and the prescriber needs this context.
Blood pressure
If not recently measured, it should be checked before starting. Uncontrolled hypertension is a contraindication.
Alcohol use
Alcohol dependency is a caution. Abrupt reduction in heavy alcohol use alongside bupropion can increase seizure risk.
FAQ
Common questions about Mysimba side effects
How long does nausea last on Mysimba?
For most people, nausea is worst in the first two to four weeks and improves significantly once the body adjusts. If it has not improved by week four or five, or is severe enough to prevent eating or drinking, speak to your prescriber. Taking tablets with food can help.
Can Mysimba cause depression or anxiety?
Bupropion affects dopamine and noradrenaline pathways and changes in mood are a known possibility. Some people report feeling more anxious, particularly in early treatment. If you notice significant changes to your mood, sleep, or thoughts, contact your prescriber. People with a history of bipolar disorder must not take Mysimba.
Is the seizure risk relevant if I have never had a seizure?
The risk is real but small for people with no relevant history — approximately 0.06% (around 1 in 1,700) in the clinical trials. The risk is significantly higher for people who have had a seizure before, which is why that history is an absolute contraindication. Your prescriber will also assess whether any other medications lower the seizure threshold further.
Can I drink alcohol while taking Mysimba?
The prescribing guidance recommends minimising alcohol intake. Alcohol lowers the seizure threshold, adding to the risk from bupropion. Abrupt cessation of heavy alcohol use while starting Mysimba is particularly concerning — discuss your alcohol intake honestly with your prescriber.
Important
Information only
Tablet Compare is information only. Mysimba is a prescription-only medicine requiring clinical assessment. Speak to a registered clinician before starting any treatment. Avoid unregulated sellers.