Smartweed (Polygonum hydropiper), also known as water pepper, has a long history of use in traditional herbal medicine, particularly in North America, Europe, and Asia. In folk medicine, it has been employed for a variety of purposes, including as a diuretic, which is the likely basis for its use in supporting or treating edema (fluid retention). The diuretic action, according to traditional sources, is believed to help promote urination and thereby reduce excess fluid in the body. Early herbal texts and ethnobotanical records mention the use of smartweed teas or poultices to address "dropsy," the historical term for edema.

However, scientific evidence for the efficacy and safety of smartweed in treating edema is extremely limited. There are only a few laboratory studies examining its phytochemical content and general pharmacological actions, and none provide robust clinical data supporting its use as a diuretic in humans. The available research is insufficient to confirm its effects on fluid balance or its safety profile. Therefore, while smartweed is traditionally used for this purpose, the evidence is weak and does not meet modern scientific standards.

In summary, the use of smartweed for edema is supported primarily by tradition, with minimal scientific validation. Caution is advised, and consultation with a healthcare professional is recommended before use.