The term "adaptogen" was coined by N. V. Lazarev in 1947, a Russian toxicologist. It refers to any substance that allows the subject to counteract stressors — of any type — through non-specific resistance, i.e., adaptation to the stress, be it chemical, metallic, electromagnetic, or organic, such as bacterial, viral, parasitic, or fungal infections. The stress could also be personal, such as due to overwork, overconsumption, or athletic exertion; and the stress could be emotional, such as due to grief, fear, loss, and other factors. To be an adaptogen, the herb or supplement must have as close to zero side effects as possible, i.e., it cannot interfere with normal physiological functions. Of the Ayurvedic herbs, it is generally conceded that ashwagandha and tulsi (holy basil) are the two best adaptogens, but all rasayanas have some adaptogenic properties.