products, or using the wrong type, can cause diarrhea.

Also ask him if he is consuming alot of Gatorade (has fructose in it), or other sugar products. Some protein powders athletes use already have magnesium in them. Combine this with a supplement and you get diarrhea (I have seen this scenario happen).

Fructose intolerance gives symptoms similar to IBS.
Also some foods now have sorbitol in them and this is a laxative and gives problems. So you have to read labels carefully.

Panic/anxiety/OCD sometimes responds to inositol. This is a simple easy thing to try.
We use the powder here, I buy very inexpensively at iherb. But it can be expensive locally.

Start at 500mg a day and increase to about 2 gm/daily slowly to see where he needs it. It mixes into
any drink and is tasteless. This has helped my husband immeasureably.
I wouldn't go above 3-5 grams a day without a doctor's supervision. Some psychiatrists use up
to 15 grams a day. (I really can't imagine THAT!).