The term adaptogen is used by herbalists to refer to a natural herb product that is proposed to increase the body's resistance to stress, trauma, anxiety and fatigue. In the past, they have been called rejuvenating herbs, qi tonics, rasayanas, or restoratives. All adaptogens contain antioxidants, but antioxidants are not necessarily adaptogens and that is not proposed to be their primary mode of action. The concept of adaptogens dates back thousands of years to ancient India and China, but modern study did not begin until the late 1940s. In 1947, Nikolai Lazarev defined an adaptogen as an agent that allows the body to counter adverse physical, chemical, or biological stressors by raising nonspecific resistance toward such stress, thus allowing the organism to "adapt" to the stressful circumstances.