Paroxetine - Adverse Effects

Adverse Effects

Sexual dysfunction is a common side effect with SSRIs. Specifically, side effects often include difficulty becoming aroused, lack of interest in sex, and anorgasmia (trouble achieving 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Although usually reversible, these sexual side effects can last for months or years after the drug has been completely withdrawn. This is known as post SSRI sexual dysfunction.

Among the common adverse effects associated with paroxetine treatment of depression and listed in the prescribing information, those with the greatest difference from placebo are nausea (26% on paroxetine vs 9% on placebo), somnolence (23% vs. 9% on placebo), ejaculatory disturbance (13% vs. 0% on placebo), other male genital disorders (10% vs. 0% on placebo), asthenia (15% vs. 6% on placebo), sweating (11% vs. 2% on placebo), dizziness (13% vs. 6% on placebo), insomnia (13% vs. 6% on placebo), dry mouth (18% vs. 12% on placebo), constipation (14% vs. 9% on placebo), and tremor (8% vs. 2% on placebo). Other side effects include high blood pressure, headache, agitation, weight gain, impaired memory and paresthesia, decreased fertility.

General side effects are mostly present during the first 1–4 weeks while the body acquires a tolerance to the drug, although once this happens, withdrawal can cause a rebound effect with symptoms re-emerging in an exaggerated form for very long periods of time. Almost all SSRIs are known to cause either one or more of these symptoms. A person receiving paroxetine treatment may experience a few, all, or none of the listed side-effects, and most side-effects will disappear or lessen with continued treatment, though some may last throughout the duration. Side effects are also often dose-dependent, with fewer and/or less severe symptoms being reported at lower dosages, and/or more severe symptoms being reported at higher dosages. Increases or changes in dosage may also cause symptoms to reappear or worsen.

On 9 December 2004, the European Medicines Agency's (EMEA) Committee for Medicinal Products for Human Use (CHMP) informed patients, prescribers, and parents that paroxetine should not be prescribed to children. CHMP also gave a warning to prescribers recommending close monitoring of adult patients at high risk of suicidal behaviour and/or suicidal thoughts. CHMP does not prohibit use of paroxetine with high risk adults but urges extreme caution. Due to reports of adverse withdrawal reactions upon terminating treatment, CHMP recommends to reduce gradually over several weeks or months if the decision to withdraw is made. See also Discontinuation syndrome (withdrawal).

Cases of akathisia and activation syndrome have been observed during paroxetine treatment.

Rarely serotonin syndrome, a severe adverse effect may occur.

Paroxetine and other SSRIs have been shown to cause sexual side effects in most patients, both males and females. In males, paroxetine is also linked to sperm DNA fragmentation.

Mania or hypomania may occur as a serious side effect of paroxetine, affecting up to 8% of psychiatric patients treated. This side effect can occur in individuals with no history of mania but it is more likely to occur in those with bipolar or with a family history of mania.

Schmitt et al. (2001) suggested that paroxetine negatively affects long-term memory, but not short-term, although the result has not been independently verified. In their study, healthy participants given paroxetine for 14 days (20 mg for days 1–7 and 40 mg days 8–14) showed poorer recall of words on day 14 compared to those receiving a placebo. Schmitt et al. did not take into account a significant difference in verbal recall at baseline between the paroxetine and placebo groups, however, and this difference may have been the source of the significant group difference on day 14. Moreover, participants receiving paroxetine recalled as many words at baseline as they recalled on day 14, which is not consistent with the conclusion that paroxetine negatively affects verbal recall.