Fluoxetine - Adverse Effects

Adverse Effects

Sexual dysfunction is a common side effect with SSRIs. Specifically, side effects often include difficulty becoming aroused, erectile dysfunction, lack of interest in sex, and anorgasmia (inability to achieve orgasm). Genital anesthesia, loss of or decreased response to sexual stimuli, and ejaculatory anhedonia are also possible. Although usually reversible, these sexual side effects can last for months, years, or permanence after the drug has been completely withdrawn. This is known as Post SSRI Sexual Dysfunction.

According to the manufacturer of Prozac brand of fluoxetine, Eli Lilly, fluoxetine is contraindicated in individuals taking monoamine oxidase inhibitors, pimozide (Orap) or thioridazine (Mellaril). The prescribing information recommends that the treatment of the patients with liver impairment "must be approached with caution". The elimination of fluoxetine and its metabolite norfluoxetine is about half as fast in these patients, resulting in the proportionate increase of exposure to the drug. Ibuprofen used in combination with fluoxetine can cause significant intestinal bleeding after a period of use.

Among the common adverse effects associated with fluoxetine and listed in the prescribing information, the effects with the greatest difference from placebo are nausea (22% vs 9% for placebo), insomnia (19% vs 10% for placebo), somnolence (12% vs 5% for placebo), anorexia (10% vs 3% for placebo), anxiety (12% vs 6% for placebo), nervousness (13% vs 8% for placebo), asthenia (11% vs 6% for placebo) and tremor (9% vs 2% for placebo). Those that most often resulted in interruption of the treatment were anxiety, insomnia, and nervousness (1–2% each), and in pediatric trials—mania (2%).

Similarly to other SSRIs, sexual side effects are common with fluoxetine; they include anorgasmia and reduced libido.

In addition, rash or urticaria, sometimes serious, was observed in 7% patients in clinical trials; one-third of these cases resulted in discontinuation of the treatment. Postmarketing reports note several cases of complications developed in patients with rash. The symptoms included vasculitis and lupus-like syndrome. Death has been reported to occur in association with these systemic events.

Akathisia, that is inner tension, restlessness, and the inability to stay still, often accompanied by "constant pacing, purposeless movements of the feet and legs, and marked anxiety", is a common side effect of fluoxetine. Akathisia usually begins after the initiation of the treatment or increase of the dose and disappears after fluoxetine is stopped or its dose is decreased, or after treatment with propranolol. There are case reports directly linking akathisia with suicidal attempts, with patients feeling better after the withdrawal of fluoxetine, and again developing severe akathisia on repeated exposure to fluoxetine. These patients described "that the development of the akathisia made them feel suicidal and that it had precipitated their prior suicide attempts". The experts note that because of the link of akathisia with suicide and the distress it causes to the patient, "it is of vital importance to increase awareness amongst staff and patients of the symptoms of this relatively common condition". More rarely, fluoxetine has been associated with related movement disorders acute dystonia and tardive dyskinesia.

Fluoxetine taken during pregnancy also increases rate of poor neonatal adaptation. Because fluoxetine is excreted in human milk, nursing while on fluoxetine is not recommended. A study of fluoxetine administered to newborn mice found that early postnatal exposure of the drug later caused the adult mice to exhibit depressive and anxious behavior similar to those of induced depression, which could be relieved by fluoxetine. The American Association of Pediatrics classifies fluoxetine as a drug for which the effect on the nursing infant is unknown but may be of concern.