Medical Health Encyclopedia

The toxic effects of levodopa with or without carbidopa are considerable.

Physical Side Effects. The physical side effects are as follows:

• Low blood pressure. Low blood pressure is a common problem during the first few weeks, particularly if the initial dose is too high. The addition of extra supplements of carbidopa reduces this effect to some degree. The patient should drink lots of fluids and possibly increase salt intake to maintain normal blood pressure.
• Arrhythmia. In some cases the drug may cause abnormal heart rhythms.
• Gastrointestinal effects. Stomach and intestinal side effects are common even with carbidopa. Taking the drug with food can alleviate the nausea. It should be noted, however, that proteins interfere with intestinal absorption of levodopa, and some physicians recommend not eating any protein until nighttime in order to avoid this interference. The drug can also cause gastrointestinal bleeding.
• Effects in the lung. Levodopa can cause disturbances in breathing function, although it may benefit PD patients who have upper airway obstruction. The mechanism of such actions is unclear.
• Hair loss.

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Psychiatric and Mental Side Effects. The major adverse effects of the drug are psychiatric. Patients taking levodopa, especially in combination with other drugs, can experience the following:

• Confusion.
• Extreme emotional states, particularly anxiety.
• Vivid dreams.
• Visual and possibly auditory hallucinations. The drug may even unmask dementia that had not been previously noticed.
• Effects on learning. L-dopa appears to have mixed effects on learning. It may actually improve working memory. However, some evidence suggests that it floods and impairs areas of the brain related to other learning functions (specifically as the ability to apply different rules of behavior in similar situations.)
• Sleepiness and sleep attacks.