Cerebral palsy, gastroesophageal reflux disease, or GERD, macroglossia and rabies can all cause excessive saliva. Other causes include mental retardation, poisoning and pregnancy, particularly with severe morning sickness, according to WebMD.
Facial paralysis due to Bell's palsy can also cause the problem. Parkinson's disease overstimulates nerves, muscles, and glands, often leading to excess saliva. Problems swallowing due to sore throat, stroke or amyotrophic lateral sclerosis, also known as ALS or Lou Gehrig's disease, can make the normal amount of saliva difficult to manage. A dentist or otolaryngologist needs to determine whether a patient is actually producing excess saliva before recommending treatment, explains Everyday Health.