Alantolactone is a sesquiterpene lactone compound predominantly found in the root of Inula helenium (elecampane). Historically, elecampane has been used in traditional European and Chinese medicine for its expectorant and anti-inflammatory properties, particularly for respiratory ailments such as cough, bronchitis, and sinus congestion. The basis for its use in congestion stems from anecdotal reports and centuries of traditional herbal practice, where decoctions or extracts of elecampane root were administered to help clear mucus and ease breathing.

Scientifically, while alantolactone has demonstrated some anti-inflammatory, antimicrobial, and immunomodulatory effects in preclinical studies, there is a lack of direct clinical evidence supporting its efficacy specifically for sinus congestion in humans. The available studies mostly focus on its broader biological activities rather than targeted relief of congestion or sinusitis. Thus, its use for sinus congestion is primarily based on traditional usage rather than robust scientific validation. The overall evidence rating is low, reflecting the absence of well-designed human clinical trials for this specific indication.