Hello there - As @bobcurly has already said, an increased thirst can be common on this class of medication, due to the way ot is designed to work. Whilst taking it, it is imporrtant your husband takes on board plenty of fluids as dehydration won't help how he feels and could increase the chances of him experiencing unpleasant side effects, like urine infections or thrush..
Ive been on this for a year now, my diet was spot on and im in the gym most days but metformin just wasnt working, i now take both and my blood sugar plummeted and stayed there. As is said, take plenty of water throughout the day and take the canag early on