hi,Asalamo alaikum. mostly dark urin is due to 1 . less intake of water with medicine(dehdration) 2 taking any B complex with your drug which is water soluble so it gives colour to urin but in your case is 3.
kidney filter toxins out of your system and many of them are extreated through kidney.This give colouration to urin SO take lot of water along the medicine.( warm water as you have
cough) ok take care