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Adaptogens or adaptogenic substances, compounds, herbs or practices refer to the pharmacological concept whereby administration results in stabilization of physiological processes and promotion of homeostasis, for example, decreased cellular sensitivity to stress. The European Medicines Agency states in a 2008 reflection paper that the concept requires additional clinical and pre-clinical research, and is therefore not accepted into current terminology.
Normal pharmacological theory supports the receptor theory of drug mechanism, and the scientific community calls into question the validity of the concept of adaptogens, while the U.S. Food and Drug Administration (FDA) and European Medicines Agency accept that the term can be used to assess traditional products.
In herbal medicine the categorization of different herbs as adaptogens is very popular, often with far-reaching claims of increasing longevity, libido and well-being. Most of the studies conducted on adaptogens were performed in the Soviet Union, Korea, and China during the 1980's. These studies have been criticized for various methodological flaws.
The concept of adaptogens was originally created by pharmacologist N.V. Lazarev in 1947 to describe novel effects of dibazol 12-benzyl benzimidazol, an arterial dilator developed in France. Adaptogenesis was later applied in the former Soviet Union to describe remedies that increase the resistance of organisms to biological stress in experimental and clinical studies. According to the original definition, adaptogens are:
non-specific remedies "that increase resistance to a broad spectrum of harmful factors (stressors) of different physical, chemical and biological natures".
This definition has been updated and today adaptogens are conceptualized as a:
"new class of metabolic regulators (of a natural origin) which increase the ability of an organism to adapt to environmental factors and to avoid damage from such factors."
Another definition requires that, for an herb to be considered an adaptogen, it must be nontoxic, nonspecific and have a normalizing effect on physiology.
By 1984, more than 1,500 pharmacological and clinical published studies had been conducted on adaptogens in the USSR, Adaptogens have even been described as "medicine[sic] for healthy people". In 1998, the term "adaptogen" was allowed as a functional claim for certain products by U.S. Food and Drug Administration and the European Medicines Agency claims, "The concept of adaptogens is sufficient to be considered in the assessment of traditional herbal medicinal products (e.g., monograph on Eleutherococcus root)." However they concluded saying "The HMPC is aware of the fact that numerous pre-clinical and clinical studies have been performed with the view to proving the concept of an adaptogen. However, the clinical data have a number of shortcomings such as deficiencies in the description of inclusion and exclusion criteria, description of the medication, diagnosis, study design, analysis etc.
There is dispute in the herbal community regarding what qualifies as an adaptogen. However, the following are generally believed to qualify:
- American Ginseng (Panax quinquefolius), root
- Ashwagandha (Withania somnifera), root
- Asian Ginseng (Panax ginseng), root
- Cordyceps (Cordyceps sinensis), mushroom/mycelium
- Dang Shen (Codonopsis pilosula, C. tangshen), root
- Eleuthero (Eleutherococcus senticosus), root/stem bark
- Green Chirayta (Andrographis paniculata), leaves
- Guduchi (Tinospora cordifolia), root/stem
- Holy Basil (Ocimum sanctum, O. gratissimum), herb
- Jiaogulan (Gynostemma pentaphyllum), herb
- Licorice (Glycyrrhiza glabra, G. uralensis), root
- Reishi (Ganoderma ludicum), mushroom/mycelium
- Rhaponticum (Rhaponticum carthamoides), root
- Rhodiola (Rhodiola rosea), root
- Schisandra (Schisandra chinensis), fruit/seed
- Siberian Ginseng (Eleutherococcus Senticosus), root,
- Shilajit (Asphaltum bitumen), pitch 
- Shiitake (Lentinula edodes)
Adaptogens in other cultures
The concept of adaptogens as "medicine for the healthy" or as a substance that helps the body cope with stress is a similar to many remedies common in chinese herbology, as well as other forms of traditional medicine.
Ayurveda traditional medicine operates with the concept of rasayana. Various substances are classified in this tradition as rasayanas, meaning they are believed to promote physical and mental health, improve defense mechanisms of the body and enhance longevity. Rasayanas are referred to as adaptogens by some researchers. 
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