What is the cause of a metallic taste in my mouth when i run?

Gum disease: One scenario in which a person may notice a metallic taste in the mouth while exercising involves unhealthy oral hygiene. Gingivitis and tooth or gum infections include tasting metal as a symptom. Though the bad taste may be present at other times, it is likely that the symptom is magnified when the body is under the added physical stresses of exercise.

Multiple possibility: Running increases your blood presure and could be causing an underlying infection to exude into your mouth. This is often described as a metalic taste. Medications are exuded in the saliva and this is a possible source. A visit with your dentist is advisable.