Anti-inflammatory and antioxidant activity of carvacrol in the respiratory system: A systematic review and meta-analysis.

Carvacrol is a monoterpene present in the essential oil of a number of plants and has been widely used in traditional medicine because it is considered to have a range of therapeutic effects including in relation to respiratory disease. To conduct a systematic review and meta-analysis to assess the anti-inflammatory and antioxidant activities of carvacrol when used in the treatment of respiratory disorders. A comprehensive literature search using Scopus, MEDLINE-PubMed, Cochrane and Web of Science was undertaken. Papers related to the anti-inflammatory or antioxidant properties of carvacrol in the treatment of an injury in the respiratory system in in vivo studies and published in the period up to and including August 2019. A total of 152 studies were initially identified, with only 17 meeting the inclusion criteria. Five of the studies were performed in humans, and 12 were performed in rodents. Among the 17 studies included in the systematic review, we performed the meta-analysis with nine of the studies with animals. Carvacrol had a positive effect on the reduction of interleukin (IL)-1beta, IL-4, IL-8 and malondialdehyde (MDA); however, the analysis indicated that carvacrol had no effect on IL-6 and tumor necrosis factor alpha (TNF-alpha), probably due to the methodological quality of the studies and their heterogeneity. Current evidence supports the antioxidant and anti-inflammatory effects of carvacrol, but its relationship with the reduction of some inflammatory mediators in animals with lung injury needs further elucidation.