Dry mouth is a medical condition that often goes undiagnosed. It occurs when the salivary glands stop working effectively. Dry mouth can be caused by a number of factors, including more than 400 prescription and over-the-counter medications. People who suffer from dry mouth often report waking up thirsty, having difficulty chewing, swallowing or speaking. They may use gum, hard candy, water or lip balm to try to replace or increase salivation.