What causes a metallic taste in the mouth?

Several things. Most common dental cause is a draining tooth or gum abscess. Next common is a reaction to some medication. Sinus infections draining pus can do this too. B & c vitamin deficiencies and zinc deficiency may be associated withbmetallic tastes. There are many patients in whom no cause of metallic taste can be found. See your dentist to rule out dental infections as your first step.