Marshmallow cough syrup – physical effects

The use of the aqueous extract of marshmallow root for respiratory symptoms has been described for the first time by Pliny the Elder [ 1 ], prominent victim of the outbreak of Mt. Vesuvius in 79 AD. STW 42 (Phytohustil ®​ ), a cough syrup based on this extract, has characterized analytically [ 2 ] [ 3 ], as well as their anti-inflammatory effects [ 4 ] [ 5 ] [ 6 ], but still, their physical effects [ 7 ] are key for their fast and strong action in irritative cough [ 8 ]. To characterize these, physical parameters were studied in comparison to 5 other liquid cough preparations available in the German market. STW 42 and the other liquid cough preparations (coded 1-5) were studied by rotational viscosimetry and regarding their retention on a mucosal surface (EpiOral resp. ex vivo) after labelling with [14C]-galactose and repeated rinsing, mimicking the effect of swallowing saliva on the pharyngeal mucosa. The viscosity of the preparations tested was in a range of 482-26 mPas, ranking in order of decreasing viscosity STW 42>2>1>3>4. The order of retention was (in decreasing order) STW 42>4>1>5>2>3. Comparison of the viscosity values with epithelial retention data indicated that viscosity alone did not account for the retention on epithelial tissues. The results confirm the unique physical properties of marshmallow cough syrup and so underline its usefulness in irritative cough already described by Pliny the Elder and confirmed since then by a huge body of evidence. Acknowledgements Many thanks to Jens Seibel, Marcus Frieler and Konstanze Bedal for fruitful discussions. Publication History Article published online: 05 March 2026 © 2026. Thieme. All rights reserved. Georg Thieme Verlag KG Oswald-Hesse-Straße 50, 70469 Stuttgart, Germany