My father (72) was prescribed diacerein for a minor arthritis on his small finger 10 days ago. he is now feeling unwell for 5 days (diarrhea, vomit, lack of appetite, dark urine). can it be the medication? if he stops it, when back to normal?

Stop it right away. GI side effects are common with this drug and it can rarely affect hepatobilary system which results in dark urine (high bilirubin in blood). From NIH website: "The use of diacerein is associated with common gastrointestinal disorders such as soft stools and diarrhoea, common mild skin reactions, and, uncommonly, hepatobiliary disorders". Side effects should resolve.

Sop the med and let his MD know right away.