How long does it normally take for the Lactulose to be effective in relieving the constipation symptoms. My mother is on Taxol, chemo, this is her third week, with severe cramping (constipation ?) last week which led her to initially take the Lactulose. After sitting on the toilet all day, it finally worked last thursday, however it caused her to have a Prolapsed Rectum. Yesterday she received her chemo again, and again today is experiencing severe cramps which she is calling constipation. Just wondering if it is truely constipation, or is cramping a side effect of the chemo Taxol? how long can we normally expect the Lactulose to take effect?