If a bad taste in the mouth is metallic, it can indicate certain cancers, as well as diabetes, kidney problems or liver problems, states the Cleveland Clinic. People already receiving cancer treatment may experience a bad taste from chemotherapy or radiation.
Another possible cause of a bad taste in the mouth, particularly metallic, is side effects from prescription or over-the-counter drugs, according to the Cleveland Clinic. In the beginning stages of pregnancy, women might find their taste changes, resulting in bad or metallic tastes in the mouth. Dementia, chemical exposure and infections are all other possible causes of a bad taste in the mouth.