Hi, Thanks for posting in HCM. I understand your concern. Miralax contains polyethylene glycol. It is a laxative solution that increases the amount of water in the intestinal tract to stimulate bowel movements. Hence, it is used as a laxative to treat occasional constipation or irregular bowel movements. The most common side effects which can be encountered with its use include: Abdominal cramps, flatulence, frequent bowel movements, nausea, stomach pain or bloating. However, it does not alter the colour of the stool. In case the symptoms do not subside and become bothersome, you need to seek medical attention promptly. Hope the information provided would be helpful. All the best.