I have recently been diagnosed with myeloproliferative neoplasm, favor essential thrombocythemia (no stainable iron). I have had some gastrointestinal problems a couple of times in the past. The medicine prescribed for the former was hydroxyurea, 500 mg every other day. On the first day I took the pill & had diarrhea an hour later, then at 8:00PM I had a black tarry stool. I also had began taking the prescribed 325 mg iron the same day. A black tarry stool is mentioned in the drug literature that came with the med. A friend of mine scoffs that I was concerned & have seen my hematologist today ( 6 days later), saying that black tarry stools mean cancer - and "you don't have cancer". She makes me feel embarrassed for reporting it but the doctor has ordered a colonoscopy (shouldn't it be an endoscopy?)