Severe sleepiness and excess sleep duration induced by paroxetine treatment is a beneficial pharmacological effect, not an adverse reaction.

Severe sleepiness and excess sleep duration, "Hypersomnia", induced by paroxetine treatment are generally considered adverse drug reactions, however, our experience indicates that patients with depressive disorder who experience "Hypersomnia" during paroxetine treatment have good clinical response. The aim of this study was to determine if "Hypersomnia" during paroxetine treatment is a beneficial pharmacological effect or an adverse drug reaction, and to investigate the impact of genetic polymorphisms on individual differences in the occurrence of "Hypersomnia" induced by paroxetine. A consecutive series of 46 Japanese patients with depressive disorder were treated with paroxetine. Patients who complained of great drowsiness or who slept for more than 12-h per day over seven days were identified as having experienced "Hypersomnia". For the clinical improvement rates and genotype distribution of the circadian locomotor output cycles kaput (CLOCK), serotonin transporter and cytochrome P450 2D6 (CYP2D6), the group that showed "Hypersomnia" induced by paroxetine treatment and the group that did not show "Hypersomnia" were compared statistically. Patients who experienced "Hypersomnia" (17.4%) showed a significantly higher response rate at two weeks than did patients who did not experience "Hypersomnia" (p=0.0127). No significant association between the occurrence of "Hypersomnia" and genetic polymorphisms was found. We cannot exclude the risk of false positive errors due to the relatively small sample sizes. "Hypersomnia" during paroxetine treatment for depression is a beneficial pharmacological effect, not an adverse drug reaction.