Hi @naiviv, I have not tried magnesium oxide for my running battle with constipation but there is an older discussion started by @ellamster that you might want to read through to learn what has been shared.

-- Chronic bowel problems, Magnesium and Side effects:
https://connect.mayoclinic.org/discussion/chronic-bowel-problems/
Also, here's some information on the topic that might be helpful:
-- Magnesium Oxide in Constipation:
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7911806/
I'm trying to get my constipation under control for an upcoming inguinal hernia surgery and have been taking Miralax daily but still have issues. I recently found a member in another discussion that mentioned Heather's Tummy Fiber Organic Acacia Senegal for IBS - https://www.amazon.com/dp/B0002ON8DU. I ordered some and it really has helped more than anything else that I have tried.