Drugs to improve blood flow for people who have poor blood circulation in the veins of their legs. Background. Insufficient blood circulation in the veins of the legs might be caused by genetic factors, may occur after trauma, or may result from a blood clot. Poor movement of blood up the legs may cause swelling and puffiness, feelings of heaviness, tingling, cramps, pain, varicose veins and changes in skin pigmentation. If severe insufficient blood circulation occurs, ulcers and skin wasting can develop. Drugs such as natural flavonoids extracted from plants and similar synthetic products may improve blood circulation. These drugs are known collectively as venoactive drugs or phlebotonics.