"This is the best medicine available for drug induced constipation, there is no doubt in my experience.  My one concern is that it does involve some urinary retention, certainly when I was given the maximum dose of 12mg.  The lower dose of 8mg caused less urinary retention but I am only using Relistor once a week until we assess how much retention it is causing, by ultrasound.  The manufacturer is still saying urinary retention is not a side effect. I note the comment of urinary retention here.  This could be a serious problem for those of us with underlying disease that involves urinary retention, such as ALD or some forms of MS, for example. Relistor is a great help otherwise."