In recent years, the antiparkinsonian drug regime has become increasingly complicated. A wide range of antiparkinson agents is meanwhile available. Combination therapies may unfortunately induce interactions up to the point of life-threatening events. The potential of drug-drug interactions must be taken into account before starting a patient on combination treatment. Moreover, the frequent multimorbidity of patients with Parkinson's disease necessitates the application of additional drugs. A general overview is difficult to maintain because of the countless number of possible interactions. Cautious proceeding is certainly indicated in particular cases. The most common interactions will be discussed below. We should bear in mind that many of the interactions related to drug combinations are unknown yet.