After oral ingestion, it is absorbed in the small intestine. Absorption can be delayed by meals and increased gastric acidity. Absorbed levodopa is not bound to plasma protein.
Nerve cells can use levodopa to make dopamine and replenish the brain's dwindling supply.
Dopamine cannot be given directly because it doesn't cross the blood-brain barrier, the elaborate meshwork of fine blood vessels and cells that filters blood reaching the brain. Levodopa crosses the blood-brain barrier by way of the large neutral amino acid carrier transport system. Levodopa is used to treat the stiffness, tremors, spasms, and poor muscle control of Parkinson's disease. Usually levodopa is given combined with carbidopa . When added to levodopa, carbidopa delays the conversion of levodopa into dopamine until it reaches the brain, preventing or diminishing some of the side effects that often accompany levodopa therapy.