I have suffered with constipation for many years. My strategy was to take every 5th day a massive dose of Senna tea. This had effect after 12 hours. But my gastro-enterologist adviced against Senna it being an irritant. He prescribed Lactulose. I take 4 table spoons in the morning on an empty stomach. It has effect after 7 hours. To make the stool softer I also insert a glycerine suppository 3 hours before I expect to have a BM. This method works for me.