Is it normal for amitza to work slowly throughout the day i notice it's better then miralax (polyethylene glycol). ?

Sounds fine: Different laxative-type medications have varying effects on different people. If Amitiza (lubiprostone) is working better, one can talk about that with one's doctor, and perhaps use the Amitiza (lubiprostone) as one's main medication for chronic constipation. Linzess is similar to Amitiza (lubiprostone), as both slow the body's absorption of water from the stool in the intestine, thus preventing the stool from getting drier.