The active principles or constituents (phytochemicals) in medicinal plants are chemical compounds known as secondary plant products. Some secondary products discourage herbivores; others inhibit bacterial or fungal pathogens. Active principles in medicinal plants may affect health, but are not-essential nutrients as our diet does not require them to sustain life in the same way as vitamins and minerals.
"A Note on Variation of Active Principles in Indian Medicinal Plants and TIM Formulations,"
1, Article 80.
Available at: http://opensiuc.lib.siu.edu/ebl/vol2008/iss1/80