Took 400mg of presc magnesium this am before starting colonoscopy prep. noticed suprep has magnesium. is it ok that i took magnesium supplement.

Magnesium: Taking oral magnesium should not interfere with your colonoscopy.

Probably ok: The magnesium supplement you took was probably eliminated during the bowel cleansing process, which uses a magnesium-based laxative such as magnesium citrate. The magnesium in the bowel prep isn't absorbed by the body but passes through the intestines and causes the bowel-cleansing cathartic effect. Check with your pcp or gastroenterologist.