Carbidopa is a medication commonly used in combination with levodopa to treat symptoms of Parkinson's disease. It works by preventing the conversion of levodopa into dopamine before it reaches the brain, allowing more levodopa to enter the central nervous system and improve motor function. By inhibiting the enzyme that breaks down levodopa, carbidopa helps reduce side effects such as nausea and vomiting that can occur when levodopa is taken alone. This combination therapy enhances the effectiveness of treatment, making it easier for patients to manage their symptoms and improve their quality of life.