Aescin, the main active compound of horse chestnut (Aesculus hippocastanum) seed extract, has been studied for its effects on venous disorders, including phlebitis (inflammation of veins). The scientific rationale for its use lies in aescin's anti-inflammatory, anti-edematous, and venotonic properties. Several clinical studies and meta-analyses have evaluated horse chestnut seed extract (which contains standardized amounts of aescin) in chronic venous insufficiency (CVI) and related conditions; some of these studies include patients with superficial phlebitis.

The mechanism of action is believed to involve the reduction of capillary permeability and improvement of venous tone, which may decrease swelling and inflammation in affected veins. Some randomized controlled trials have shown that aescin can reduce symptoms such as leg pain, edema, and heaviness, which are also common in phlebitis.

However, while the evidence is stronger for its use in CVI and varicose veins, direct high-quality studies focused specifically on aescin for the treatment of phlebitis are limited. Some older studies and reviews note improvement in phlebitis symptoms with aescin, but more targeted research is needed to fully establish efficacy for this condition. Overall, the use of aescin for phlebitis is supported by moderate scientific evidence, primarily extrapolated from studies in related venous disorders.