According to the Diagnostic and Statistical Manual of Mental Disorders, 5th Edition: DSM-5, anxiety disorders share immoderate feelings of fear and anxiety features – as psychological disturbances - and related physiological perturbations (Park and Kim, 2020, Schuyler, 2016). This disorder, which is thought to be the most common psychiatric disorder and has been on the rise in recent decades, often remains undertreated, leading to feelings of restlessness, early fatigue, impaired concentration, and an increased risk of cardiovascular disease (Lépine, 2002, Tully et al., 2016). Anxiety can impose significant morbidity and mortality through functional impairment, decreased quality of life, alcohol and substance abuse, depression, cardiovascular disability, and suicide (Bachmann, 2018, Schuyler, 2016, Tully et al., 2016).

Owing to the potential effectiveness, tolerability and possible non-interaction, and low cost, many patients with various diseases seek traditional and herbal medicine interventions to control and treat disorders. This tendency is higher in patients with psychiatric disorders than in patients without a medical history of psychiatry (Mamtani and Cimino, 2002).

Lavandula is an evergreen perennial shrub of the family Lamiaceae that originates from the Mediterranean region (Jianu et al., 2013, Prusinowska and Śmigielski, 2014). Lavender has received a great deal of attention from researchers in herbal medicine, and many in-vitro, animal, and clinical studies have been conducted on its intervention. Jianu et al. (2013) examined the antimicrobial properties of lavender essential oil. They found a significant bactericidal effect against bacteria such as Shigella flexneri, Staphylococcus aureus, and Escherichia coli (Jianu et al., 2013). In another study, Hajhashemi et al. studied the anti-inflammatory and analgesic properties of the leaf extracts and essential oil of L. angustifolia. They found that some essential oil components can have anti-inflammatory and analgesic effects (Hajhashemi et al., 2003). A clinical trial conducted on 80 patients with depression disorder treated with citalopram, showed that infusion of 5 g of dried shoots of L. angustifolia had positive therapeutic effects on these patients and reduced mean depression score (Nikfarjam et al., 2013). A study on patients who wanted to remove their wisdom teeth under local anesthesia also showed that inhaling lavender essential oil could reduce peri-operative anxiety (Karan, 2019).

As mentioned earlier, many studies have been conducted to evaluate the effectiveness of lavender on various disorders, one of the most important and notable of which is anxiety. These studies have compiled data for several systematic reviews (SRs) with or without meta-analysis (MA), assessing the generalizability of the results. These studies had been conducted with different methods and qualities affecting their validity. No study has so far collected and reviewed the evidence generated by these SRs and evaluated their quality. Therefore, this study aims to systematically review SRs with or without MAs investigating the anxiolytic effects of lavender in humans and to evaluate the methodological quality of the studies conducted.