Multivitamin or iron tabs can cause discoloration but not so much. Maybe pain killer abuse leading to Gastric Bleed. Consult

Sir u will immediately have to stop this pain killer & in future too you should not use any NSAID drugs means non steroidal anti inflammatory drugs unless prescribed !! Black stools may mean altered blood in stool !! Get your stool tested for occult blood along with HbA1c , KFT & CBC & urine routine examination done since u r diabetic & have hydronephrosis too !! Stop any blood thinning agents if taking like ecosprin & disprin & glycomet if using for diabetes !! Take following drugs for the time being TAB NEKSIUM 40 OD BBF TAB CALPOL 650 FOR PAIN SUGAR FREE ANTACID GEL LIKE STOPACID OR GELUSIL 4TSF BD FOR 3 DAYS & REPORT AVOID HOT SPICY FOOD TEA COFFEE & HARD DRINKS SUGAR

Iron intake turns stool to black colour. Also gastric bleeding can lead to black coloured stools. Any other symptoms like pain in abdomen vomitings gastritis?

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After taking Iron, stool color wl be black. Don't worry it's normal.stop for 5days stool color wl become normal.