Yes...especially iron. When I was pregnant, I took high doses of iron...my stools would turn greenish/black. Stop taking the vitamins for a while and see is they return to normal. ...give it a week....and if your stool does not seem right,,,,then go to your dr. & get checked out.
Also b vitamins turn your urine bright yellow.
Don't know for sure, but I would think that anything you put down your throat could have an effect.