Don't worry for your black stool, but yes if it is persists there may be mixed with altered blood. So first do one thing, investigate RE stool first. If there Occult Blood +, then need treatment and it is because any ulcer
in intestine or due to liver problem. If no! Then don't worry.
If yes, take Leptendra6/one dose Bd until cure. And investigate LFT for better diagnosis. If and problem! Then add Carduus M Q/15 ml, 10 drops bd with half cup of water
with the first medicine. Report after 10 days. If not cured! Then need Endoscopy. But I do think you will be recovered by these two medicines after investigate RE stool and LFT. Thanks.