The anxiolytic efficacy of the orally administered lavender oil preparation Silexan was investigated in generalized anxiety disorder (GAD) in comparison to placebo and paroxetine. In this randomized, double-blind, double-dummy trial 539 adults with GAD according to DSM-5 criteria and a Hamilton Anxiety Scale (HAMA) total score ⩾18 points participated and received 160 or 80 mg Silexan, 20 mg paroxetine, or placebo once daily for 10 wk. The primary efficacy endpoint was the HAMA total score reduction between baseline and treatment end. The HAMA total score decreased by 14.1 ± 9.3 points for Silexan 160 mg/d, 12.8 ± 8.7 points for Silexan 80 mg/d, 11.3 ± 8.0 points for paroxetine, and 9.5 ± 9.0 points for placebo (mean ± s.d.). Silexan 160 and 80 mg/d were superior to placebo in reducing the HAMA total score (p < 0.01) whereas paroxetine showed a trend towards significance (p = 0.10) in the full analysis set. The difference between paroxetine and placebo was more pronounced in the analysis of observed cases (HAMA total score reduction: p < 0.01). In the Silexan 160 mg/d group 73/121 patients (60.3%) showed a HAMA total score reduction ⩾50% of the baseline value and 56 (46.3%) had a total score <10 points at treatment end, compared to 70/135 (51.9%) and 45 (33.3%) for Silexan 80 mg/d, 57/132 (43.2%) and 45 (34.1%) for paroxetine, and 51/135 (37.8%) and 40 (29.6%) for placebo. In addition, Silexan showed a pronounced antidepressant effect and improved general mental health and health-related quality of life. Incidence densities of adverse events (AEs) were 0.006 AEs/d for Silexan 160 mg/d, 0.008 AEs/d for 80 mg/d, 0.011 AEs/d for paroxetine, and 0.008 AEs/d for placebo. In GAD Silexan is more efficacious than placebo. AE rates for Silexan were comparable to placebo and lower than for the active control paroxetine.