Fluoxetine: What is it? Mechanism of Action, Side Effects and Dosage

It is a medication used to treat depression, panic attacks, obsessive-compulsive disorder, bulimia, and a severe form of premenstrual syndrome.

Brands and classes

  • Marcas comerciales: Prozac, Sarafem, Prozac Weekly, Selfemra.
  • Generic name: fluoxetine.
  • Drug class: Antidepressants, ISRS.

What is fluoxetine?

You are in a class of drugs called selective serotonin reuptake inhibitors (SSRIs), a category that includes citalopram (Celexa), paroxetine (Paxil), and sertraline (Zoloft).

Mechanism of action

Fluoxetine affects neurotransmitters, the chemicals that brain nerves use to communicate with each other.

Neurotransmitters are manufactured and released by the nerves and then travel and adhere to nearby nerves. Therefore, neurotransmitters can be considered as the communication system of the brain. Serotonin is a neurotransmitter that is released by nerves in the brain.

Serotonin travels through the space between the nerves and attaches to receptors on the surface of nearby nerves or attaches to receptors on the surface of the nerve that produced it to be absorbed by the nerve and rereleased (a process known as reuptake).

Many experts believe that an imbalance between neurotransmitters is the cause of depression. Fluoxetine works by preventing the reuptake of a neurotransmitter, serotonin, by nerve cells after release.

Since uptake is an important mechanism to eliminate released neurotransmitters and end their actions on adjacent nerves, the reduced uptake caused by fluoxetine increases the free serotonin that stimulates nerve cells in the brain.


Like fluoxetine, it increases the amount of circulating serotonin available in your brain; altering the balance of chemicals in the brain can help alleviate depression symptoms, eating disorders such as bulimia, and obsessive-compulsive disorder and can improve your mood, sleep, appetite, and energy level.

By relieving these symptoms, you can help restore your interest in daily life.

Fluoxetine is available under the following brands: Prozac, Sarafem, Prozac Weekly, and Selfemra.

Possible side effects

Side effects of Fluoxetine can be a priority on your list of concerns. Discover the likelihood that you have problems taking this antidepressant.

Side effects of fluoxetine are widespread (affect more than 1 in 10 people):

  • Difficulty sleeping ( insomnia ).
  • Headache.
  • Feeling sick (nausea)
  • Diarrhea.
  • Fatigue.

Fluoxetine dose

Doses available in capsules for pediatric and adult use:

  • 10mg, 20mg, 40mg.

Doses available in tablets for pediatric and adult use:

  • 10mg, 20mg, 60mg.

Capsule, delayed-release: (dose only for adults):

  • 90mg.

Fluoxetine Oral Solution:

  • 20mg / 5ml.

Special considerations:

Major depressive disorder:

Prozac: 20mg taken each day orally, may consider increasing the dose gradually after several weeks at 20 mg/day; It should not exceed 80mg per day.

Prozac weekly: 90mg orally every week.

Children over eight years old: 10mg – 20mg orally per day, initially starting at 10 mg/day in children with lower weight, can gradually increase the dose after one week; It should not exceed 20mg per day.

Obsessive-compulsive disorder:


Prozac: 20mg orally every day; may consider the gradual increase in dose after several weeks at 20mg / day (20mg – 60mg / day recommended range); It should not exceed 80mg per day.

Prozac weekly: 90mg orally every week.

For children over seven years: 10 mg orally per day, initially; You can gradually increase the dose after two weeks to 20mg per day; more increases can be considered after several weeks.

Adolescents and children of greater weight: typical dose range 20mg – 60mg per day.

Children of lower weight: typical dosage range 20mg – 30mg per day.

Bulimia nervosa:

  • Initial or maintenance: you can adjust the dose to 60mg orally every day for several days.

Panic disorder: initially 10mg orally every day during the first week, then 20mg orally every day. You may consider increasing the dose gradually after several weeks; it should not exceed 60mg per day; doses higher than 60 mg/day are not evaluated.

Premenstrual dysphoric disorder:  20mg orally every day initially; you can gradually increase the dose; it should not exceed 80 mg/day, or intermittent (Sarafem), 20 mg orally every day, beginning 14 days before menstruation and until the first full day of menstruation (repeat each cycle).


  • 20mg – 80mg orally every day.

Dosing considerations: efficacy may be increased with concomitant amitriptyline.


  • 20mg – 40mg orally every day.

Hot flashes caused by hormonal chemotherapy:

  • 20 mg/day orally for four weeks.

Raynaud Phenomenon:

  • 20mg – 60mg / day orally.

Modifications of doses

After stopping therapy, gradually decrease for 4-6 months to minimize the incidence of withdrawal symptoms and allow the detection of re-emerging symptoms.

If the withdrawal symptoms are intolerable, after a dose reduction, resume the previously prescribed dose and decrease the amount at a more gradual rate.

Renal impairment: be careful; drugs can accumulate with severe kidney failure.

Hepatic insufficiency ( cirrhosis ): decreased clearance of the original drug and the active metabolite (norfluoxetine); recommended lowest or least frequent dose.

Considerations of the geriatric dosage

Initial 10mg orally per day; you can gradually increase the dose by 10mg – 20mg after several weeks as tolerated. Do not take it at night unless sedation occurs.

Preferred drug of choice in older adults concerning tricyclic antidepressants due to the lower amount of side effects.