Sinemet Parkinson's disease drug. Packet of Sinemet pills, a prescription drug used to relieve the symptoms of Parkinson's disease. The active ingredients are levodopa and carbidopa. These work together to increase the levels of dopamine in the brains of sufferers, without increasing the levels in the body, which would cause tiredness and drowsiness. The dopamine levels in people suffering from Parkinson's disease are known to be reduced and this is thought to be the cause of some of the symptoms of the disease.