Since the publication of Il Brekhman’s landmark articles in 1969, adaptogen research has proceeded. Brekhman himself continued studying the adaptogens he had previously identified. Independent researchers have also investigated Brekhman’s adaptogens. Indeed, drugs like Eleutherococcus senticosus, Panax ginseng, Rhodiola rosea, and Schizandra chinensis have been scrutinised by researchers around the world. In addition, researchers have used Brekhman’s criterion to identify additional adaptogens; botanical drugs like Withania somnifera have surfaced through these efforts. To develop an appreciation for the adaptogen concept, and Brekhman’s adaptogen criterion, this chapter applies his criterion to five well?researched drugs: Eleutherococcus senticosus, Panax ginseng, Rhodiola rosea, Schizandra sinensis, and Withania somnifera. Although his research focused on Eleutherococcus senticosus and Panax ginseng, of the aforementioned tonic drugs, the first four botanical drugs were identified by Brekhman as adaptogens. Brekhman did not study Withania somnifera is an adaptogen, but it is revealed to be one by applying his criterion.