Thick saliva may simply be due to the fact that you're not drinking enough water. It may also be a sign of dry mouth (xerostomia). Health problems -- such as cancer treatment, diabetes, high blood pressure, and Sjögren's disease and other conditions that affect the salivary glands in the mouth -- may also cause dry mouth. It's also a side effect of many drugs. If your thick saliva is bothersome or does not go away, talk to your doctor.