After taking prilosec, stools started turning black, the day after i quit taking it they were brown again. this has happened before the same way.

Black stools...: Black stools can either be from foods or medicines ingested or a sign of GI tract bleeding. Common foods that cause black stools include collard greens and beets. Medicines associated with black stools include bismuth containing products (e.g. Pepto-bismol) and iron supplements. Prilosec does not cause black stools. I suggest you see your doctor to rule out GI bleeding.