** Pyrovalerone ** (Centroton, 4-Methyl-β-keto-prolintane, Thymergix, O-2371) is a central nervous system (CNS) stimulant that acts as a norepinephrine–dopamine reuptake inhibitor (NDRI). It was developed in the 1980s and had briefly been approved in Spain and France for chronic fatigue or lethargy and as an appetite suppressant, but was withdrawn from both markets around 2001 due to safety concerns including problems with abuse and dependence. It is closely related on a structural level to a number of other cathinone stimulants, such as α-PVP, MDPV and prolintane. Side effects of pyrovalerone include decreased appetite, anxiety, fragmented sleep or insomnia, and trembling, shaking, or muscle tremors. Withdrawal symptoms following abuse upon discontinuation often results in depression. The R-enantiomer of pyrovalerone is devoid of pharmacologic activity.