Vasicine is an alkaloid primarily found in the plant Justicia adhatoda (also known as Vasaka or Malabar nut). Its use in the treatment of cough has roots in traditional Ayurvedic medicine, where extracts of the plant have been used as expectorants and bronchodilators for centuries. Scientific research has since provided a mechanistic basis for these traditional uses. Preclinical studies have shown that vasicine possesses bronchodilatory, expectorant, and antitussive properties. Vasicine acts as a bronchodilator by inhibiting phosphodiesterase, leading to relaxation of bronchial smooth muscles. It also stimulates the respiratory tract, thereby enhancing the clearance of bronchial secretions, which is beneficial for productive coughs.

Animal studies and some human trials have demonstrated that vasicine and its derivatives (such as vasicinone) can increase mucociliary clearance and reduce symptoms of cough. Its efficacy has been compared to theophylline, a well-known bronchodilator, with some studies indicating comparable or even superior activity. However, large-scale and high-quality clinical trials in humans are limited, and most evidence comes from in vitro studies, animal models, or small human studies. As a result, while there is scientific validation supporting its use for cough, the overall strength of evidence is moderate rather than robust.