Sweet flag (Acorus calamus) has a longstanding history of use in traditional medicine systems such as Ayurveda and Traditional Chinese Medicine (TCM) for the treatment of respiratory ailments, including dry cough. In Ayurveda, the rhizome of sweet flag, known as "Vacha," is considered to have expectorant, antitussive, and anti-inflammatory properties. Traditional formulations often incorporate sweet flag to soothe the throat, reduce irritation, and facilitate the expulsion of phlegm, although its direct use for "dry" cough is more commonly based on its general action on respiratory symptoms and its demulcent effect.

In TCM, sweet flag (Shi Chang Pu) is sometimes used to "transform phlegm" and "open orifices," but its application for dry cough specifically is less emphasized compared to its use for wet cough or other respiratory conditions. There is limited scientific literature directly supporting its effectiveness for dry cough; most modern studies focus on its antimicrobial, anti-inflammatory, and neuroprotective effects, rather than its role in treating coughs. Thus, while sweet flag's use for dry cough is primarily justified by tradition, and there is anecdotal and historical evidence for its inclusion in traditional cough remedies, robust clinical studies confirming its efficacy for this specific indication are lacking. Therefore, the evidence rating is moderate (2 out of 5), reflecting tradition-based use with minimal direct scientific validation.