Objective: To compare the efficacy and safety of paroxetine controlled release (CR) (12.5 mg/day or 25 mg/day) versus placebo in premenstrual dysphoric disorder (PMDD).Method: A double-blind, randomized, placebo-controlled trial was conducted over 3 menstrual cycles in women aged 18-45 years with confirmed DSM-IV PMDD in 47 outpatient centers across the United States and Canada from November 1999 to January 2002. The primary efficacy measure was the visual analog scale (VAS)-Mood, which is the mean of 4 core symptoms: irritability, tension, depressed mood, and affective lability.Results: A statistically significant difference was observed in favor of paroxetine CR 25 mg versus placebo on the VAS-Mood (adjusted mean difference = -12.58 mm, 95% CI = -18.40 to -6.76; p < .001) and for paroxetine CR 12.5 mg versus placebo (adjusted mean difference = -7.51 mm, 95% CI = -13.40 to -1.62; p = .013). Paroxetine CR was generally well tolerated.Conclusion: Paroxetine CR doses of 12.5 mg/day and 25 mg/day are effective in treating PMDD and are well tolerated.