Located deep within the brain, the substantia nigra normally manufactures dopamine, a chemical needed by the brain to transmit to your muscles the messages necessary for smooth, controlled movements. A large percentage of dopamine-producing cells must be affected before the symptoms of Parkinson's appear. The process can take years. Although no cure exists for Parkinson's disease, a variety of effective medications may provide dramatic relief of symptoms. Individuals typically react differently to a given drug, so it may take time for your doctor to tailor the combination and dosage of drug therapies.
Nerve cells can use levodopa to make dopamine and replenish the shortfall in the brain.
Dopamine can't be given directly because the compound doesn't cross the barrier that separates circulating blood from the brain. Levodopa is usually given along with carbidopa. Carbidopa delays the conversion of levodopa into dopamine until it reaches the brain, thereby helping to diminish some of the side effects of levodopa therapy. Carbidopa also can reduce the amount of levodopa needed to control symptoms. First introduced in the 1960s, levodopa delays the onset of disabling symptoms.