The term adaptogen was coined in the mid-20th century by the Soviet scientist Nicolai Lazarev and further developed by his student Israel I. Brekhman. The term refers to a substance that can help the body adapt to stress, regardless of the source: heat, cold, exertion, trauma, sleep deprivation, toxic exposure, radiation, infection, or psychological duress. By definition, an adaptogen also causes no side effects, treats a wide variety of illnesses, and helps return an organism back toward balance (homeostasis) no matter in what manner it has moved out of balance.
Perhaps the only indisputable example of an adaptogen is a healthful lifestyle. By eating right, exercising regularly, and generally living a life of balance and moderation, you will increase your physical fitness and ability to resist illnesses of all types. Whether there are any herbs that provide such universal health benefits, however, remains unproven (and, on the face of it, unlikely). Nonetheless, advocates of the adaptogen concept believe that a variety of herbs have this property, especially ginseng (both Panax ginseng and Eleutherococcus senticosus), as well as ashwagandha, astragalus, maitake, reishi, rhodiola, schisandra, and suma.