Senokot Syrup - Senna is known as a 'stimulant laxative'. It acts on nerve endings in the gut wall. These nerves then make the muscles in the intestine contract with more force and more often. When the gut contracts, it moves the contents along faster, and so it reduces constipation. As senna increases the activity of the muscle in the gut, it often causes stomach cramps. Senna is given by mouth and takes 8-12 hours to work.