There is hardly a Parkinson's patient who does not know them: The gastrointestinal complaints, i.e. those affecting the gastrointestinal tract. 

These include

Dysphagia = swallowing disorders
Sialorrhea = the involuntary discharge of saliva from the mouth
Gastroparesis = Stomach paralysis or delayed emptying of the stomach
Constipation = constipation

The symptoms appear years to decades before the onset of the motor symptoms.

Gastroparesis occurs in seventy to one hundred percent of patients. According to PD Dr. Lisa Klingelhöfer from the Clinic for Neurology at the University Hospital Dresden, a clear connection with the severity of the motor symptoms. The consequences are usually weight loss, malnutrition and dehydration. To make matters worse, in the case of disturbed peristalsis and absorption, a delayed or, in the worst case, no effect of the oral Parkinson's medication is to be expected.