The use of the Sichuan Pagoda Tree (Styphnolobium japonicum, formerly Sophora japonica) for phlebitis (inflammation of veins) is primarily rooted in traditional Chinese medicine (TCM). In TCM, the flower buds of this plant, known as "Huai Hua Mi," have been used historically to "cool the blood" and treat various bleeding and vascular disorders, including hemorrhoids and some forms of vascular inflammation. The traditional rationale is based on its purported ability to clear heat and reduce toxicity, which is thought to correlate with anti-inflammatory effects in modern terminology.

Scientific studies have identified several bioactive compounds in the pagoda tree, such as rutin and quercetin, which have demonstrated anti-inflammatory and vasoprotective properties in laboratory and animal models. However, direct clinical evidence supporting its efficacy specifically for phlebitis in humans is lacking. Most available research focuses on its broader effects on blood vessels and inflammation rather than controlled trials for phlebitis. Therefore, while there is a plausible pharmacological basis and traditional precedent, robust scientific validation for its use in treating phlebitis is limited.

In summary, the use of Sichuan Pagoda Tree for phlebitis is justified mainly by traditional practices, with some laboratory evidence suggesting potential benefit, but there is insufficient clinical research to strongly support its use for this specific condition.