My son didn't take polyethylene glycol 3350 (Miralax) related to Parkinson's, but sure did have terrible constipation when he was littler, more due to not getting a lot of fiber with his picky eating habits. The doctor prescribed an increase at one time which my mother-in-law warned me about. I figured that it was fine, but he had a definitely messy situation that could have been a real embarrassment. So, my observation is that slow changes might be wise.