Zeitschrift für Phytotherapie 2019; 40(S 01): S18
DOI: 10.1055/s-0039-1697281
Georg Thieme Verlag KG Stuttgart · New York

Action of the aqueous willow bark extract STW 33-I in joint and muscle pain – well established

O Kelber
1   Innovation & Development, Consumer Health, Bayer Phytomedicines Supply and Development Center, Steigerwald Arzneimittelwerk GmbH, Darmstadt, Germany
MT Khayyal
2   Pharmacology Department, Faculty of Pharmacy, Cairo University, Cairo, Egypt
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09. September 2019 (online)


Willow bark extracts are used e.g. in joint and muscle pain. As they contain a large number of polar constituents, the salicylates being the basis of their standardization, relevance of these for the mode of action is a matter of interest, especially with regard to the use of aqueous willow bark extracts as STW 33-I. Therefore a literature review was conducted, focused on the mode of action of willow bark extracts and fractions thereof.

This review revealed a considerable number of pharmacological studies [1], including in vitro and in vivo studies in different pharmacological models [2], supporting the assumption that especially the polar fractions of the extract contribute to the action. Salicylic acid derivatives and their metabolites [3], together with different other polyphenols, were identified as relevant for the mechanisms of action, as was also confirmed by gene expression analyses [4].

Accordingly, the studies on the mode of action of the aqueous willow bark extract STW 33-I show, that its action is based on more than just tradition, given the broad available evidence on willow bark and the salicylates, and can be well explained even on a molecular level.


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[3] Knuth S et al. Planta Med 2013; 79: 1489 – 1494

[4] Ulrich-Merzenich G et al. Phytomedicine 2012; 19: 930 – 939