Loss of neurons in the brain that use dopamine to communicate is one of the hallmark features of Parkinson’s disease (PD), causing slowness, stiffness, tremor, and balance problems. Replacing the brain’s dopamine is therefore one of the key treatment strategies to help improve the motor symptoms of PD. Dopamine itself does not cross the blood-brain barrier and therefore can’t be used to treat PD. Instead, levodopa, a precursor of dopamine, which does cross the blood-brain barrier is used. If levodopa is ingested by itself however, it breaks down in the bloodstream before it crosses into the brain, so levodopa is typically ingested with another medication that stops it from breaking down. In the US, the combination of carbidopa/levodopa is used. When levodopa is taken with carbidopa, much lower doses of levodopa can be consumed and side effects such as nausea are minimized. Carbidopa/levodopa is the mainstay of treatment for PD and is the most effective medication available for PD. APDA research funding played a role in the discovery of levodopa for PD treatment, when we funded the work of Dr. George C. Cotzias back in the 1960s.
