Final answer:
Levodopa is used to treat Parkinson's disease by increasing dopamine levels, but can cause side effects if given alone. A peripheral decarboxylase inhibitor, such as carbidopa, is used alongside levodopa to minimize these side effects and improve efficacy.
Step-by-step explanation:
When levodopa alone is given to a patient with Parkinson's disease, it can increase dopamine levels in the brain. However, this can lead to non-targeted areas of the brain receiving too much dopamine, which can cause side effects like psychosis or symptoms resembling schizophrenia. To avoid this, a peripheral decarboxylase inhibitor is often administered alongside levodopa. This inhibitor prevents the conversion of levodopa to dopamine outside of the central nervous system, thereby reducing unwanted side effects and allowing more levodopa to reach the brain where it is needed. Carbidopa is a common drug paired with levodopa for this purpose.