Fluoxetine (Prozac)

Other names: Prozac. Several non branded versions are also available.

Fluoxetine is one of the class of SSRI (selective serotonin reuptake inhibitor) drugs. It is normally prescribed for depression. Exploratory studies have also looked at whether fluoxetine might have a role in reducing inflammation around nerves in multiple sclerosis. Although some effect was recorded, larger studies have failed to find any benefit of fluoxetine in progressive MS.

Fluoxetine was one of three drugs studied in the MS-SMART trial, which involved 440 people with secondary progressive MS. Participants took amiloride(a treatment for high blood pressure and heart disease), riluzole (a treatment for motor neurone disease), fluoxetine or a placebo pill for two years. MRI scans and other clinical measures such as walking, eyesight and simple thinking tests were done before and after treatment to test for signs of MS disease progression. Researchers found no clinical effect of the three drugs being tested. Although the three drugs in MS-SMART were not found to be effective, the trial was valuable in helping researchers to design clinical trials which compare several treatments to placebo at the same time. It has also enhanced our understanding of the biology of progressive MS.

A separate clinical trial also failed to show a neuroprotective effect of fluoxetine in people with primary or secondary progressive MS.

How fluoxetine works

Fluoxetine works by increasing the stimulation between some cells in the brain.

How do I take fluoxetine?

Fluoxetine is taken orally, as tablets. Dosages vary and it is normally prescribed by a GP.

Fluoxetine is a long-term treatment. Individuals should allow four to six weeks to feel the benefit of fluoxetine.

Fluoxetine remains in the body for some weeks after an individual has stopped taking the drug, therefore, individuals should not stop abruptly but taper off treatment with a doctor's advice.

Side effects and contraindications

Side effects include:

  • dizziness or lightheadedness particularly on getting up from a lying or sitting position
  • dry mouth
  • decreased sexual drive or ability
  • diarrhoea
  • drowsiness
  • headache
  • trouble sleeping
  • abnormal dreams
  • fast or irregular heartbeat
  • frequent urination
  • menstrual pain
  • tiredness or weakness
  • tremor
  • vomiting

Most of these are transitory and will go away once someone has adjusted to the medication.

Fluoxetine can interfere with sleep, so is best taken in the morning. It can upset the stomach and may be taken with or after food.

Fluoxetine should not be taken by people with reduced liver function, acute heart conditions, diabetes, history of bleeding disorders, or a history of some types of mental health problems. It should also not be taken during pregnancy or when still breastfeeding.

Fluoxetine can interact with other medications that affect the central nervous system, notably carbamazepine, phenytoin and diazepam, affecting the rate at which they are absorbed.

Find out more

Shafey H.
The effect of fluoxetine in depression associated with multiple sclerosis.
Canadian Journal of Psychiatry 1992;37(2):147-148.
Summary (link is external)
Mostert JP, et al.
Effects of fluoxetine on disease activity in relapsing multiple sclerosis: a double-blind, placebo-controlled, exploratory study.
Journal of Neurology Neurosurgery and Psychiatry 2008;79(9):1027-1031.
Summary (link is external)
Cambron M, et al.
Fluoxetine in progressive multiple sclerosis: The FLUOX-PMS trial
Multiple Sclerosis Journal 2019;25(13):1728–1735.
Summary (link is external)
Chataway J, et al.
Efficacy of three neuroprotective drugs in secondary progressive multiple sclerosis (MS-SMART): a phase 2b, multiarm, double-blind, randomised placebo-controlled trial.
Lancet Neurology 2020 Mar;19(3):214-225.
Full article (link is external)
On this page