Constipation is a condition of the digestive system where an individual has hard feces that are difficult to expel. It generally occurs because too much water is absorbed from food. The slower the food moves through the digestive tract, the more water the colon will absorb from it. Consequently, the feces become dry and hard. Causes of constipation include physical inactivity, certain medications, and aging. The following medicines are used for treatment of constipation.