Abstract: 4,4-Diarylpiperidine compounds, preferably 4,4-diphenylpiperidine which are substituted or unsubstituted in the 1-position of the piperidine nucleus, such as 1-(lower alkyl)-4,4-diphenylpiperidines, 1-(lower alkyl)-4-phenyl-4-tolylpiperidines, and their substantially non-toxic, pharmaceutically-acceptable acid addition salts, are highly effective central nervous system (CNS) stimulants which are superior to known amphetamine-type stimulants. A novel and highly advantageous process of making such 4,4-diarylpiperidine compounds comprises reacting a 4-aryl-4-hydroxypiperidine compound which may be substituted in its 3-position by an aroyl group, with an aromatic hydrocarbon, in particular with benzene, in the presence of a Friedel-Crafts-type catalyst.