The use of Malabar Nut Tree Leaf Extract (from Justicia adhatoda, also known as Vasaka) for cough is supported by both traditional and scientific evidence. Traditionally, it has been used in Ayurvedic and Unani medicine for centuries as a remedy for respiratory conditions, particularly cough, bronchitis, and asthma. The leaves contain alkaloids such as vasicine and vasicinone, which are credited with bronchodilatory, expectorant, and antitussive properties.

Scientific studies support these traditional uses. Research has demonstrated that vasicine possesses significant bronchodilator and expectorant activity, facilitating the expulsion of mucus and easing breathing. Various in vivo and in vitro studies, including animal models, have shown that extracts of Justicia adhatoda reduce cough frequency and severity, likely due to their action on the respiratory tract's smooth muscles and mucous membranes. Reviews and pharmacological studies published in peer-reviewed journals (e.g., Phytotherapy Research, Journal of Ethnopharmacology) have documented these effects, with some clinical trials indicating benefit in acute and chronic bronchitis.

While high-quality, large-scale clinical trials in humans are limited, the combination of strong traditional use and modern pharmacological evidence justifies its use for cough relief. Regulatory authorities in several countries recognize its inclusion in over-the-counter cough syrups and expectorants.