Umckalin is a natural coumarin compound found in the roots of Pelargonium sidoides, a plant traditionally used in South African medicine for respiratory ailments. Modern scientific research has focused on standardized extracts of P. sidoides, especially in the form of Umckaloabo, which contains umckalin as one of its key constituents. Several randomized controlled trials and meta-analyses have evaluated the efficacy of P. sidoides extracts in treating acute bronchitis and other respiratory tract infections.

The evidence suggests that these extracts can modestly reduce the duration and severity of symptoms such as cough and sputum production in acute bronchitis, likely due to their antimicrobial, immune-modulating, and mucolytic properties. European Medicines Agency (EMA) and other regulatory bodies recognize P. sidoides extracts as a traditional herbal medicinal product for relieving symptoms of common cold and acute bronchitis. However, it should be noted that while umckalin is present in these extracts, most studies investigate the whole extract rather than umckalin in isolation.

Overall, the use of umckalin-containing extracts for supporting the bronchial system is justified by moderate scientific evidence, primarily extrapolated from studies on P. sidoides rather than umckalin alone. Therefore, the evidence rating is 3 out of 5.