Strongest evidence: Lavender has high-strength evidence for improving sleep quality (8 of 8 studies, moderate effect size) and moderate-strength evidence for reducing anxiety (7 of 8 studies, moderate effect size). For sleep, studies predominantly used inhaled lavender essential oil over 5–7 days. For anxiety, effective doses ranged from 100–500 mg/day orally or 2–15 minutes of daily inhalation over 4–8 weeks.
Mixed or weaker evidence: Two outcomes — reduced fatigue and reduced depression symptoms — each have only 3 studies, all reporting benefit but with low to moderate evidence strength. For fatigue, all studies used inhalation in clinical populations (e.g., hypertension, chemotherapy patients) over a median of 7 days. For depression, study reporting was incomplete, with no doses, forms, or durations consistently provided, limiting actionable conclusions.
Effective dose patterns: Consistent dose information is only available for anxiety, where oral doses of 100–500 mg/day or inhalation sessions of 2–15 minutes daily showed benefit. For sleep, most studies used nightly inhalation (e.g., 2 minutes to 20 minutes before bed) but did not specify a single standard dose. No effective dose is reported for fatigue or depression.
Population insights: The strongest evidence comes from clinical populations: adults with hypertension, postmenopausal women, pregnant women, patients undergoing chemotherapy, and older adults with sleep disorders. Effects are less clear for general healthy populations, and no studies focused on deficient or specific subgroups.
Notable caveats: A major concern across all outcomes is publication bias — null-result studies are less likely to be published. Additionally, many studies used inhalation rather than oral forms, making it difficult to generalize findings across delivery methods. Median study durations were short (7–28 days), so long-term effects remain unknown. The evidence base for fatigue and depression is very small (3 studies each) and should be considered preliminary.