A dry mouth and tongue at night may be caused by certain types of medications, several medical conditions and breathing through the mouth while sleeping, as listed by About Health. Those experiencing mouth dryness should be evaluated by a health care professional to determine an exact cause.
Diuretics, which include medications used to treat heart failure, blood pressure and foot swelling, may cause mouth dryness as a side effect, according to About Health. Anticholinergic drugs have the same effect and include diphenhydramine sleeping medications and antidepressants. Medications are a likely cause of mouth dryness if the side effect appears with an increased dose or when the patient begins taking a new medication. Medical conditions that may cause a dry tongue include Sjorgen's syndrome, lupus, diabetes and sicca syndrome, and patients with these conditions generally experience other symptoms in addition to dry mouth.
Breathing through the mouth often occurs in conjunction with snoring and may result from an obstruction of the nasal passages, according to About Health. This obstruction may be caused by allergies, upper respiratory infections or an abnormal nasal structure. Patients may experience more severe dry mouth when sleeping on the back or after consuming alcohol. Treatment for dry mouth varies depending on the cause, but it may include medications, surgery and mouth moisteners.