Vasicine is a quinazoline alkaloid found primarily in the plant Adhatoda vasica (also known as Malabar nut). It has a long history of use in traditional Ayurvedic and Unani medicine as a remedy for respiratory ailments, including bronchitis, asthma, and cough. The scientific interest in vasicine stems from its bronchodilator, expectorant, and mild antimicrobial properties, which have been investigated in preclinical studies. Laboratory and animal studies demonstrate that vasicine can relax bronchial smooth muscle, increase bronchial secretions (helping to clear mucus), and inhibit histamine-induced bronchospasm. Some studies also indicate mild antibacterial activity against respiratory pathogens.

However, direct clinical evidence supporting the use of vasicine or Adhatoda vasica extracts specifically for pneumonia in humans is limited. Most data come from in vitro or animal models, and while these suggest a potential for benefit in respiratory infections, robust, controlled human studies are lacking. In summary, the use of vasicine for pneumonia is supported by some scientific rationale and preclinical findings, but high-quality clinical trials are needed to establish efficacy and safety in this context. Thus, the evidence rating is moderate-low (2/5), reflecting preclinical promise but a lack of convincing human data.