[7] Common side effects include drowsiness, dry mouth, loss of appetite, sweating, trouble sleeping, and sexual dysfunction.

[7] While the rate of side effects appears similar compared to other SSRIs and SNRIs, antidepressant discontinuation syndrome may occur more often.

[23][24][25] Despite this, there was no clear evidence that paroxetine was better or worse compared with other antidepressants at increasing response to treatment at any point in time.

[27][page needed] Several studies have concluded that paroxetine is superior to placebo in the treatment of panic disorder.

[40] In 2013, low-dose paroxetine was approved in the US for the treatment of moderate-to-severe vasomotor symptoms such as hot flashes and night sweats associated with menopause.

[41] Studies have also shown paroxetine "appears to be well-tolerated and improve the overall symptomatology in patients with fibromyalgia", but is less robust in helping with the pain involved.

[42][43] Common side effects include drowsiness, dry mouth, loss of appetite, sweating, insomnia, and sexual dysfunction.

[7] While the rate of side effects appears similar compared to other SSRIs and SNRIs, antidepressant discontinuation syndromes may occur more often.

Central and peripheral 5-HT3 receptor stimulation is believed to result in the gastrointestinal effects observed with SSRI treatment.

[66][67] Babies born to women who used paroxetine during the first trimester have an increased risk of cardiovascular malformations, primarily ventricular and atrial septal defects.

[74] Common withdrawal symptoms for paroxetine include nausea, dizziness, lightheadedness and vertigo; insomnia, nightmares, and vivid dreams; feelings of electricity in the body, as well as rebound depression and anxiety.

[75][76][77] In 2002, the U.S. FDA published a warning regarding "severe" discontinuation symptoms among those terminating paroxetine treatment, including paraesthesia, nightmares, and dizziness.

Plasma, serum, or blood concentrations of paroxetine may be measured to monitor therapeutic administration, confirm a diagnosis of poisoning in hospitalized patients or to aid in the medicolegal investigation of fatalities.

Plasma paroxetine concentrations are generally in a range of 40–400 μg/L in persons receiving daily therapeutic doses and 200–2,000 μg/L in poisoned patients.

Such reactions have been observed with SNRIs and SSRIs alone, but particularly with concurrent use of triptans, MAO inhibitors, antipsychotics, or other dopamine antagonists.

[88] Based on evidence from four weeks of administration in rats, the equivalent of 20 mg paroxetine taken once daily occupies approximately 88% of serotonin transporters in the prefrontal cortex.

[13] GlaxoSmithKline has paid substantial fines, paid settlements in class-action lawsuits, and become the subject of several highly critical books about its marketing of paroxetine, in particular, the off-label marketing of paroxetine for children, the suppression of negative research results relating to its use in children, and allegations that it failed to warn consumers of substantial withdrawal effects associated with the use of the drug.

[98] The legal discovery process also uncovered evidence of deliberate, systematic suppression of unfavorable Paxil research results.

One of GSK's internal documents read, "It would be commercially unacceptable to include a statement that efficacy [in children] had not been demonstrated, as this would undermine the profile of paroxetine".

[99] In 2012, the United States Department of Justice fined GlaxoSmithKline $3 billion for withholding data, unlawfully promoting use in those under 18, and preparing an article that misleadingly reported the effects of paroxetine in adolescents with depression following its clinical trial study 329.

GlaxoSmithKline may also face actions from other generic manufacturers who incurred losses as a result of the anticompetitive conduct.

[108] In 2007, sales had dropped slightly to 18.1 million but paroxetine remained the fifth-most prescribed antidepressant in the U.S.[109][110] Brand names include Aropax, Paretin, Brisdelle, Deroxat, Paxil,[111][112] Pexeva, Paxtine, Paxetin, Paroxat, Paraxyl,[113] Sereupin, Daparox and Seroxat.

In particular, intravaginal ejaculation latency time (IELT) was found to increase 6- to 13-fold, which was somewhat longer than the delay achieved by the treatment with other SSRIs (fluvoxamine, fluoxetine, sertraline, and citalopram).

Although the evidence is conflicting, paroxetine may be effective for the treatment of dysthymia, a chronic disorder involving depressive symptoms for most days of the year.

[121] There is evidence to support that paroxetine selectively binds to and inhibits G protein-coupled receptor kinase 2 (GRK2) in mice with heart failure.