Fluoxetine: 7 things you should know
Medically reviewed by C. Fookes, BPharm. Last updated on Mar 14, 2019.
1. How it works
- Fluoxetine is a medicine that may be used to treat several conditions associated with mood. Experts aren't sure exactly how it works but believe its effects are due to its ability to block the reuptake of serotonin by nerves. This results in an increase in serotonin concentrations in the nerve synapse (the space between two nerves).
- The activity of fluoxetine against other neurotransmitters appears much less than some other antidepressants.
- Fluoxetine belongs to a group of medicines called Selective Serotonin Reuptake Inhibitors (SSRIs).
- May be used in the treatment depression and to help maintain relief from depression in adults and children aged 8 to 18 years.
- May be helpful for the relief of symptoms of obsessive-compulsive disorder (OCD) in adults and children aged 7 to 17 years.
- May be useful in the treatment of the eating disorder, bulimia nervosa, to relieve moderate-to-severe symptoms such as binge-eating and vomiting.
- Has been used to treat panic disorder in adults, with or without agoraphobia (an extreme avoidance of situations that could cause panic).
- May also be used in the treatment of premenstrual dysphoric disorder (PMDD) - a condition characterized by severe depressive symptoms, irritability, and tension prior to menstruation.
- Less likely to cause weight gain than some other antidepressants; may cause weight loss.
- Less likely to cause sedation than some other antidepressants; may cause insomnia (sleeplessness).
- Generic fluoxetine is available.
If you are between the ages of 18 and 60, take no other medication or have no other medical conditions, side effects you are more likely to experience include:
- Anxiety, a lack of energy, drowsiness or insomnia, diarrhea, indigestion, increased sweating, nausea, tremor, headache, weight loss or a decreased appetite, dry mouth, a rash, restlessness and a decreased libido are the more commonly reported side effects.
- As with other antidepressants, fluoxetine may increase the risk of suicidal thoughts or behavior; the risk is higher in children and young adults aged less than 24. Monitor for worsening mood.
- Fluoxetine may cause drowsiness or impair your judgment and affect your ability to drive or operate machinery. Avoid these tasks if fluoxetine has this effect on you.
- Interaction or overdosage may cause serotonin syndrome (symptoms include mental status changes [such as agitation, hallucinations, coma, delirium], fast heart rate, dizziness, flushing, muscle tremor or rigidity and stomach symptoms [such as nausea, vomiting, diarrhea]). Another serious syndrome, called Neuroleptic Malignant Syndrome, has also been reported; symptoms include high body temperature, muscle rigidity, and mental disturbances. Discontinue fluoxetine immediately and seek urgent medical advice if this syndrome occurs.
- May increase the risk of bleeding, especially if used with other drugs that also increase bleeding risk.
- May precipitate a manic episode in people with undiagnosed bipolar disorder.
- May cause a lowering of total body sodium (hyponatremia); elderly people or people taking diuretics or already dehydrated are more at risk.
- May cause a discontinuation syndrome if abruptly stopped. Symptoms include irritability, low mood, dizziness, electric shock sensations, headache or confusion. The dosage of fluoxetine should be tapered down slowly on withdrawal.
- Rarely causes seizures.
- Few studies have evaluated the use of fluoxetine long-term.
- Seek medical advice if a rash develops while taking fluoxetine. Discontinue if a severe allergic reaction to fluoxetine occurs and seek urgent medical advice.
- May interact with a number of other drugs including other antidepressants, tramadol, bupropion, diuretics, St John's Wort, and drugs that prolong the QT interval (such as pimozide or thioridazine).
- May not be suitable for some people including those with glaucoma, bleeding disorders, a history of seizures, liver or kidney disease, the elderly, or certain heart conditions. People with diabetes may need the dosage of their medication adjusted.
Notes: In general, seniors or children, people with certain medical conditions (such as liver or kidney problems, heart disease, diabetes, seizures) or people who take other medications are more at risk of developing a wider range of side effects. For a complete list of all side effects, click here.
- May be taken with or without food. Morning dosages may decrease the risk of insomnia.
- Take fluoxetine exactly as directed by your doctor. Do not stop suddenly without your doctor's advice. Fluoxetine is best tapered down slowly on discontinuation.
- Be alert for worsening mood and suicide-related thoughts or behaviors. Seek medical advice if changes are apparent.
- Do not drive or operate machinery if fluoxetine impairs your judgment or makes you sleepy.
- Seek urgent medical advice if symptoms consistent with serotonin syndrome (such as agitation, hallucinations, fast heart rate, dizziness, flushing, nausea, diarrhea) or Neuroleptic Malignant Syndrome (including high body temperature, muscle rigidity, or mental disturbances) develop.
- Talk to your doctor immediately if you develop a rash or seek urgent medical advice with severe allergy-type symptoms such as swelling of the face or throat, or shortness of breath.
- Do not take any other medicines, including those bought over-the-counter, without first consulting a doctor or pharmacist and asking if the medicine is safe to take with fluoxetine.
- If you have diabetes, you may need to monitor your blood sugar levels more regularly on initiation of fluoxetine and with any dosage change. Talk to your doctor if your blood sugar levels are not as well controlled as they use to be.
- Talk with your doctor if you experience any:
- Unusual bruising or increased bleeding while taking fluoxetine
- Persistent headaches, confusion, weakness, or unsteadiness resulting in falls
- An increase, irregularity, or slowing of your heart rate or shortness of breath
- Eye pain or swelling or visual disturbances
- Manic behavior such as recklessness, racing thoughts, increased energy, severe difficulty in sleeping.
6. Response and Effectiveness
- Peak plasma concentrations occur within six to eight hours of a single dose. A reduction in depressive or other symptoms may be noticed within two to four weeks; however, it may take up to six to eight weeks for the full effects of fluoxetine on mood are seen.
- Because fluoxetine persists for a long time in the body, it may several weeks before dosage increases are reflected as an improvement in mood, or a reduction in side effects is seen with dosage decreases.
Medicines that interact with fluoxetine may either decrease its effect, affect how long it works for, increase side effects, or have less of an effect when taken with fluoxetine. An interaction between two medications does not always mean that you must stop taking one of the medications; however, sometimes it does. Speak to your doctor about how drug interactions should be managed. Common medications that may interact with fluoxetine include:
- Anticoagulants (blood thinners), such as warfarin, or other drugs that have blood thinning effects such as aspirin or NSAIDs
- Anticonvulsants, such as phenytoin, phenobarbital, or primidone
- Antipsychotics (such as butyrophenones, phenothiazines, or thioxanthenes) and atypical antipsychotics (eg, olanzapine, quetiapine, ziprasidone)
- Any medication that may cause drowsiness, such as benzodiazepines (eg, diazepam, lorazepam), first-generation antihistamines (such as doxylamine or promethazine), metoclopramide, or opioids (such as codeine, morphine)
- Diuretics, such as furosemide
- Medications that may affect the heartbeat by prolonging the QT interval, such as amiodarone, encainide, or flecainide
- Other antidepressants, such as tricyclic antidepressants (eg, amitriptyline), monoamine oxidase inhibitors (eg, isocarboxazid, phenelzine, and tranylcypromine), and SSRIs (eg, paroxetine, sertraline)
- Other medications that affect serotonin, such as amphetamines, fentanyl, lithium, tramadol, triptans (eg, almotriptan, eletriptan, or sumatriptan), or St. John's Wort
- Other medications that are metabolized by the same enzymes (CYP2D6) such as tricyclic antidepressants, most antipsychotics, flecainide, propafenone, or vinblastine
- Thioridazine (do not administer at the same time as fluoxetine or for 5 weeks after fluoxetine has been discontinued)
- Others, such as HIV medications (fosamprenavir, ritonavir), procyclidine, or theophylline.
Avoid drinking alcohol or taking illegal or recreational drugs while taking fluoxetine.
Note that this list is not all-inclusive and includes only common medications that may interact with fluoxetine. You should refer to the prescribing information for fluoxetine for a complete list of interactions.
Fluoxetine [Package Insert]. Revised 02/2019. Upsher-Smith Laboratories, LLC. https://www.drugs.com/pro/fluoxetine.html
Remember, keep this and all other medicines out of the reach of children, never share your medicines with others, and use fluoxetine only for the indication prescribed.
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