Dry mouth is a common side effect of many prescription and nonprescription drugs, including drugs used to treat depression, anxiety, pain, allergies, and colds (antihistamines and decongestants), obesity, acne, epilepsy, hypertension (diuretics), diarrhea, nausea, psychotic disorders, urinary incontinence, asthma (certain bronchodilators), and Parkinson's disease. Dry mouth can also be a side effect of muscle relaxants and sedatives.