I think I am the MgO expert here
I started taking about 150mg at bed time and titrated slowly up, giving it about 3-4 days before increasing dose. It might help building up tolerance.
My end dose was 600mg daily - 200mg in the middle of the morning, in the middle of afternoon and at bed time (always away from meals since you need stomach acidity for that).
When I tried to up my bed time dose to 400mg (making it a daily total of 800mg) I got loose stools. I am also chronically constipated, but loose stools aren't fun
I just couldn't believe it didn't help with better bowel movements, but helped with many other things I had no idea it would when I first started it
I could keep with 600mg for about 5 weeks, then had to titrate down quickly and adjust potassium and calcium (with vitamin A rather than calcium itself) for a while.
The first forms of magnesium I tried were Epsom salt footbaths and oral Mg glycinate. Tried Mg glycinate in footbaths and calf sprays as well. All I got from them was a burning sensation in the ureters, breathlessness, like ammonia build up.
I also read that gut bacteria would absorb MgO poorly, so there would be a decreased risk of a flora imbalance from excess alkalinization. I guess I read it here:
http://george-eby-research.com/html/depression-anxiety.html
Please report your results back!