I'd never heard of lactulose  before. But i wouldn't consider self-medication for chronic constipation. Taking fibre supplements (soluble are easiest) is pretty harmless, and an occasional laxative is OK. But if it is chronic I would be consulting my GP &/or  colorectal specialist. A bit of research will tell what foods help or hinder bowel performance. When I had it the cause was iron tablets taken to treat anemia.  With medico approval i take a laxative once of twice a week to keep things running smoothly, so to speak :-)