There are a number of causes of constipation including lack of fiber, thyroid issues, parasites, candida, drugs, and lots of other things.

Almost all drugs cause constipation issues, but the worst are antacids, antidepressants, anesthetics, high blood pressure drugs, iron salts, and painkillers.

Things that help constipation include fiber, exercise, fluids, prunes, and dates.  Be careful with prunes as some say the active ingredient oxyphenisatin can cause liver damage.

One could consider laxatives like psyllium (the flagship colon cleanse ingredient).  Some laxatives contain carcinogens like phnolphthalein which you should avoid or senna which is suspect.

More natural 'laxatives' include flaxseed and ginger.