Only 5–10% of L-DOPA crosses the blood–brain barrier. The remainder is often metabolised to dopamine elsewhere, causing a wide variety of side effects including nausea, dyskinesias, and stiffness. Carbidopa and benserazide are peripheral dopa decarboxylase inhibitors. They inhibit the metabolism of L-DOPA in the periphery, thereby increasing levodopa delivery to the central nervous system. They are generally given as combination preparations with levodopa. Existing preparations are carbidopa/levodopa (co-careldopa, trade names Sinemet, Pharmacopa, Atamet) and benserazide/levodopa (co-beneldopa, trade name Madopar). Levodopa has also been related to a dopamine dysregulation syndrome, which is a compulsive overuse of the medication, and punding.