Side effects are common for patients who take dopamine precursors. In most cases, side effects are relatively minor, but some can be severe.

The most common side effects of the dopamine precursor levodopa (also called L-Dopa) are nausea and vomiting. Other common side effects of levodopa include dyskinesia (uncontrollable movements), sudden sleep onset, hallucinations and psychosis. Many patients taking levodopa develop dyskinesias within the first year of treatment. These can range from mild (e.g., head bobbing) to severe (e.g., violent jerking of the limbs). Motor complications occur in about half of all patients taking levodopa after 5 to 10 years of treatment.

Additional side effects may include:

• Abdominal pain
  
  
• Abnormal increase in muscular activity (hyperkinesia)
  
  
• Change in sense of taste
  
  
• Confusion
  
  
• Decreased attention span
  
  
• Diarrhea
  
  
• Difficulty sleeping
  
  
• Discoloration of sweat, urine or saliva
  
  
• Dizziness
  
  
• Drowsiness
  
  
• Dry mouth
  
  
• Fatigue
  
  
• Headaches
  
  
• Increased sweating
  
  
• Loss of appetite
  
  
• Low blood pressure upon standing (orthostatic hypotension)
  
  
• Memory loss
  
  
• Nervousness
  
  
• Nightmares
  
  
• Speaking difficulties
  
  
• Weakness

Patients who use levodopa for prolonged periods of time or who have to regularly increase dosage levels may be more likely to experience certain side effects (e.g., dyskinesia). Long-term users may also experience periods when the medication suddenly stops working for a period of time before suddenly starting to work again.

Many patients who take levodopa for restless leg syndrome initially experience an increase of symptoms during the morning, afternoon or early evening hours. This is known as augmentation. Patients who experience this side effect should consult a physician, who may recommend that the patient stop taking levodopa. In general, dopamine precursors appear to cause fewer side effects in patients who have restless leg syndrome than in patients who have Parkinson’s disease.