None. Sinemet contains levodopa (50mg) and a dopa decarboxylase inhibitor, carbidopa (12.5mg), which stops the levodopa acting outside the brain. Sinemet 62.5 is a convenient but technically inappropriate shorthand as it "mixes apples with pears". Sinemet is a branded (expensive) preparation for which the generic (cheap) alterative is called co-careldopa and like Sinemet is available as 12.5/50 and 25/100 strengths. The active ingredients of SInemet and of co-careldopa are identical.