Coumarin has been investigated for its effects on the lymphatic system, particularly in the context of lymphedema and related disorders. Scientific studies, especially those from Europe in the late 20th century, have demonstrated that coumarin can be beneficial in reducing edema by promoting the breakdown and resorption of interstitial proteins, which are a key component of lymphatic congestion. Its mechanism of action is believed to involve stimulation of macrophages, which increases proteolysis of interstitial proteins, thereby facilitating lymph flow and reducing swelling.

Clinical trials—most notably in Germany and other European countries—have shown that coumarin may be effective in treating chronic lymphedema, postmastectomy lymphedema, and other forms of lymphatic insufficiency. However, it is important to note that coumarin’s use is not without controversy, as concerns about hepatotoxicity have limited its approval and use in some countries, such as the United States, where it is not an approved medication for lymphedema. Despite this, several well-controlled studies and reviews (e.g., Rockson et al., 2000; Casley-Smith et al., 1993) continue to cite its efficacy in supporting the lymphatic system.

In summary, there is significant scientific evidence supporting the use of coumarin for lymphatic support, particularly in the management of lymphedema, although safety concerns have restricted its clinical application in some regions.