According to Lim's experiments, non-narcotic analgesics are usually considered as "peripherally" acting drugs. Conversely, most of these compounds were shown to easily cross the blood-brain barrier, and hence partly produce their effects by a central mechanism. The relative contribution of each site of action may vary from one drug to another. Aspirin-like drugs may act by inhibiting arachidonate cyclooxygenase in both the damaged tissues and the central nervous system. Finally, these drugs appear to be either selective, or dose-dependent, or nonspecific inhibitors of prostaglandin-synthetases.