Red Clover's constituents are thought to stimulate the immune system. (It has been a traditional ingredient in many formulas for cancer). Red clover has also been used to treat coughs and respiratory system congestion, because it also contains resin. Resinous substances in plants have expectorating, warming, and antimicrobial action.
Red clover also contains the blood-thinning substance coumarin. Coumarin is not unique to red clover; it is found in many other plants, including common grass. In fact, the pleasant sweet smell of freshly cut grass is due to the coumarin compounds. People on anticoagulant drugs such as Coumadin should be cautious of using red clover, as the blood may become too thin.