Black stools are usually suggestive of problem in the stomach and upper small intestine . If you have symptoms of gastritis like bloating , burning senation in the stomach and regurtitation since you started taking the multivitamin tablet. Stop the tablet and see. If black tarry stools still continues then get an stool occult blood and upper GI Endoscopy .
Next Steps
Stop medication
Start Cap.Pantocid DSR 1-0-1 before food for 1 week.
If black tarry stools still continues even after stopping medication get
1) Stool for occult blood
2) Upper GI Endoscopy
Health Tips
Stop oily and spicy food.
Stop alcohal and smoking if taking.