Patient instructed on how Levodopa and Carbidopa are used in combination to treat the symptoms of Parkinson's disease. Carbidopa prevents the breakdown of Levodopa in the bloodstream so more Levodopa can enter the brain. This can reduce some of Levodopa's side effects such as nausea and vomiting, and it may also allow your doctor to increase your Levodopa dose more quickly to find the best dose.