Guelder rose (Viburnum opulus) has a long history of traditional use in herbal medicine, particularly for its supposed effects on the muscles, especially the smooth muscles. Traditionally, preparations made from the bark, often called "cramp bark," have been used by herbalists and in folk medicine to relieve muscle cramps, spasms, and tension, most notably in the context of menstrual cramps and uterine muscle relaxation. Native American and European herbal traditions both reference the use of guelder rose for these purposes.

The rationale for these traditional uses is based primarily on anecdotal evidence and empirical observation. Some phytochemical studies have identified the presence of compounds such as coumarins, flavonoids, and valerenic acid derivatives in the bark, which may possess mild muscle-relaxant effects, but robust clinical trials in humans are lacking. The evidence supporting its use is therefore limited to traditional texts, case reports, and in vitro studies, with little high-quality human research to confirm efficacy or optimal dosing for muscle support.

In summary, guelder rose is mainly used to support the muscular system—specifically for cramping and spasm—based on traditional knowledge rather than scientific validation. The strength of the evidence is modest, warranting a low-to-moderate rating.