I have IMO which results in constipation and diarrhea as well but mostly constipation. In my case, I need to speed up motility so, I take Miralax and fiber to increase bulk. I take Sunfiber rather than Metamucil. Both increase bulk but the Sunfiber produces less gas but not as much bulk. My doctor initially suggested Metamucil but for me, the Sunfiber seems a bit better. Taking both Miralax and either fiber source each day is ok according to my doctor and dietitian.