Strongest evidence: Lavender shows the most consistent benefits for sleep quality (high evidence strength, 10 of 10 studies beneficial, moderate effect size) and anxiety (moderate evidence strength, 10 of 11 studies beneficial, moderate effect size). For fatigue, the evidence is moderate with all 4 studies reporting beneficial effects (moderate effect size). Effective doses across these outcomes typically involve inhalation of lavender essential oil for 15 minutes daily or nightly, or oral doses of 500 mg/day.
Mixed or weaker evidence: The evidence for reducing depression symptoms is low — only 3 of 4 studies reported benefit, and the single randomized controlled trial (RCT) found a neutral effect. Effect sizes were mixed (small to moderate), and no consistent dose or form was identified. Conclusions should be considered preliminary due to the small evidence base (4 studies).
Effective dose patterns: Across sleep, anxiety, and fatigue, the most common effective dose was inhalation of lavender essential oil in 15-minute daily sessions or nightly exposure (up to 8 hours). One study for sleep used oral lavender flower powder at 500 mg/day. Study durations ranged from 5 to 56 days, with median around 28 days.
Population insights: Benefits were observed across diverse clinical populations including adults with hypertension, breast cancer survivors undergoing chemotherapy, patients with hematological malignancies, postmenopausal women, older adults with sleep disorders, critically ill patients, pregnant women (c-section), children with dental anxiety, and patients with chronic heart failure or implantable cardioverter-defibrillators (ICDs). Effects appear broadly applicable rather than limited to a specific subgroup.
Notable caveats: Available evidence is subject to publication bias — null-result studies are less likely to be published. Most studies used inhalation aromatherapy, so findings may not generalize to oral lavender supplements. The evidence base for fatigue and depression is small (4 studies each), and the single RCT for depression found no effect. Study durations varied widely (5 to 56 days), and effect sizes were inconsistent across populations for some outcomes.