Knotgrass (commonly referring to species in the genus Polygonum, such as Polygonum aviculare), has a long history of use in traditional herbal medicine, including European and Asian systems, as a remedy for urinary tract and bladder concerns. Historically, knotgrass has been used as a diuretic, believed to promote urine flow and help "cleanse" the urinary tract. Some traditional sources also mention its use for cystitis and mild urinary tract irritation, likely due to its purported anti-inflammatory and astringent properties.

The rationale for its traditional use often centers around its flavonoids, tannins, and other phytochemicals, which are thought to reduce inflammation and support mucosal tissue. However, scientific studies specifically investigating knotgrass for bladder health in humans are extremely limited. A few animal and in vitro studies have indicated mild diuretic and anti-inflammatory effects, but these are not robust or directly related to bladder health or disease. There are no large, well-controlled clinical trials validating its effectiveness for urinary or bladder health.

In summary, knotgrass’s use for supporting the bladder is rooted in traditional herbal medicine, with minimal scientific validation. The evidence base is weak, and its use for this purpose should be considered as primarily traditional, rather than scientifically established.