What causes dry mouth?

Reduced saliva: Many causes: dehydration, many medications, mouth breathing, and medical conditions such as sjogren's syndrome. I would say that medications are probably the most common culprits... Keep yourself hydrated, artificial saliva may help (otc). If you take medications (antihistamines, antidepressants are very common), consult your doc... Good luck.

Many causes: It can be from excessive intake of caffeine or alcohol, not drinking enough water or related to the side effect some medications for treatment of blood pressure or mental health. Aging, post radiation treatment and some diseases like sjorgren's syndrome can also lead to dry mouth.