Can I take Fluoxetine and Venlafaxine together?

You should not take fluoxetine and venlafaxine together unless specifically instructed and closely monitored by a specialist.

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.

How to know if you're having a drug interaction

You may be experiencing a drug interaction between fluoxetine and venlafaxine if you notice:

• Agitation, restlessness or confusion.

• Shivering, sweating or fever.

• Muscle twitching or stiffness.

• Fast heartbeat.

• Diarrhoea.

• Headache.

• Feeling unusually anxious or overactive.

These can be signs of serotonin syndrome, a rare but serious reaction.

Seek urgent medical help if you have:

• High fever.

• Severe agitation or confusion.

• Seizures.

• Irregular heartbeat.

• Loss of consciousness.

What you should do

If you are experiencing any of the above symptoms you should:

• Seek emergency medical help (call 999 / go to A&E) if symptoms are severe, worsening quickly, or include high fever, confusion, seizures, or loss of consciousness.

• Do not take any further doses until you have spoken to a healthcare professional.

• Do not stop either medicine suddenly unless a doctor tells you to, as this can cause withdrawal symptoms.

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.

Important precautions

Suicidal thoughts and worsening of depression

These medicines can increase thoughts of self-harm or suicide, particularly in the first few weeks of treatment or when the dose is changed. Patients under 25 are at higher risk and must be monitored closely by family or carers.

Serotonin syndrome

Taking these with other medicines that affect serotonin (such as St John’s Wort, tramadol, or triptans for migraine) can cause a life-threatening reaction. Seek immediate medical help if you experience high fever, agitation, confusion, or muscle twitching.

Abrupt withdrawal (Discontinuation Syndrome)

Stopping these medicines suddenly can cause severe withdrawal symptoms, including 'brain zaps' (electric shock sensations), intense dizziness, and anxiety. You must taper the dose slowly under medical supervision.

High blood pressure (Hypertension)

Venlafaxine can significantly increase your blood pressure. Your doctor must check your blood pressure before you start treatment and monitor it regularly while you are taking this medicine.

Bleeding disorders or use of blood thinners

These medicines can increase your risk of bleeding, especially if you are already taking medicines that thin the blood (like warfarin) or non-steroidal anti-inflammatory drugs (like ibuprofen).

Diabetes

Fluoxetine can affect your blood sugar levels. You may need to monitor your blood glucose more closely as your dose of insulin or antidiabetic medicine might need adjusting.

Food and drink warnings

Alcohol

It is best to avoid or strictly limit alcohol while taking these medicines. Combining alcohol with antidepressants can increase drowsiness, dizziness, and coordination problems. It can also make your depression or anxiety symptoms worse.

Caffeine (Coffee, tea, energy drinks)

Fluoxetine and venlafaxine can sometimes cause jitteriness, anxiety, or difficulty sleeping. High amounts of caffeine can make these side effects worse. Monitor how you feel and consider reducing caffeine intake if you feel overly restless.

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.