Levodopa is converted to a chemical called dopamine (DOE pa meen) in the brain. Symptoms of Parkinson's disease may be caused by low levels of dopamine in the brain. Carbidopa helps prevent the breakdown of levodopa before it can reach the brain and take effect. The combination of carbidopa and levodopa is used to treat Parkinson symptoms such as muscle stiffness, tremors, spasms, and poor muscle control. This medication is also used to treat Parkinson symptoms caused by carbon monoxide poisoning or manganese intoxication. Carbidopa and levodopa may also be used for other purposes not listed in this medication guide.