Can I take Fluoxetine and Venlafaxine together?
Drug interaction guide
Originally published 25 Jan 2026
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Taking these two medicines together significantly increases the risk of a rare but serious condition called 'serotonin syndrome'. This happens when there is too much of a chemical called serotonin in your brain. Symptoms can include feeling very agitated, confused, or shaky, as well as sweating, a fast heartbeat, muscle twitching, or diarrhoea. In severe cases, it can be life-threatening.
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Why this happens
Both fluoxetine and venlafaxine work by increasing serotonin levels in the brain. When used together, their effects add up (an additive effect). Additionally, fluoxetine can slow down the way your liver breaks down venlafaxine, causing the levels of venlafaxine in your blood to rise even higher.
What you should do
You should not take these two medicines together unless specifically instructed and closely monitored by a specialist. If you are already taking both and feel unwell, seek medical help immediately. If your doctor is switching you from one to the other, they will usually advise a 'washout' period (a gap of a few weeks) because fluoxetine stays in your system for a long time.
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Using other medicines
Taking multiple medicines? Our Medicines Interaction Checker helps you check whether your prescriptions, over-the-counter medicines, and supplements are safe to take together. Simply search for your medicines to see potential interactions and what to do about them.
Disclaimer
This information is for general educational purposes only and should not be relied upon as a substitute for professional medical advice. Always consult your GP, pharmacist, or another qualified healthcare professional before making decisions about your medications. Individual circumstances may vary, and only a healthcare professional who knows your medical history can provide personalised guidance.
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Article history
The information on this page is written and peer reviewed by qualified clinicians.
25 Jan 2026 | Originally published
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