Water Pepper (Persicaria hydropiper), also known as smartweed, has a long history of use in traditional herbal medicine, particularly in Europe and Asia. It was historically employed for a variety of ailments, including as an astringent, diuretic, and for controlling bleeding. Some traditional herbal texts mention its use for "blood poisoning," which is an archaic term that could refer to septicemia or various systemic infections characterized by fever and malaise. The rationale for its use in such cases stems from its purported antimicrobial and anti-inflammatory properties, as well as its ability to "purify the blood" according to historical herbal doctrine. However, this usage is rooted primarily in folklore and pre-modern medical understanding rather than in scientific evidence.

Modern research on Water Pepper is limited, and there are no robust clinical studies validating its effectiveness in treating blood poisoning (septicemia) or related systemic infections. Some laboratory studies have identified the presence of bioactive compounds, such as flavonoids and sesquiterpenes, with mild antimicrobial or anti-inflammatory effects, but these findings do not provide sufficient support for its use in life-threatening conditions like blood poisoning. As such, while Water Pepper's use for blood poisoning is documented in some traditional sources, it cannot be considered evidence-based by current scientific standards, and its efficacy for this purpose is unproven.