Indian J Physiol Pharmacol 2009; 53 (4) : 291–306 REVIEW ARTICLE THE SCIENCE BEHIND SACREDNESS OF TULSI ( OCIMUM SANCTUM LINN.) SHANKAR MONDAL 1 , BIJAY R. MIRDHA 2 AND SUSHIL C. MAHAPATRA 1 * Departments of 1 Physiology and 2 Microbiology, All India Institute of Medical Sciences, New Delhi – 110 029 ( Received on June 18, 2009 ) Abstract : Medicinal properties of Tulsi ( Ocimum sanctum Linn) are known for thousand years to various civilizations of the world. This medicinal herb is considered as a sacred plant by the Hindus in the Indian subcontinent. Scientific explorations of traditional belief of medicinal properties of Tulsi have got momentum mostly after the middle of the 20 th century. In the present review, efforts have been made to sum up different aspects of scientific studies on this medicinal plant. Scientific evidences are available on various medicinal aspects i.e. antimicrobial, adaptogenic, anti- diabetic, hepato-protective, anti-inflammatory, anti-carcinogenic, radio- protective, immunomodulatory, neuro-protective, cardio-protective, mosquito repellent etc . to name a few. Most of these evidences are based on in-vitro, experimental and a few human studies. Key words : medicinal plant antimicrobial properties adaptogenic immunomodulation *Corresponding Author : scm@aiims.ac.in, scmahapatra@gmail.com INTRODUCTION Tulsi is described as sacred (1) and medicinal plant in ancient literature (2). The name Tulsi is derived from ‘Sanskrit’ , which means “matchless one” (3). This plant belongs to the family Labiatae , characterized by square stem and specific aroma. Botanical name of Tulsi is Ocimum sanctum (Linn). In India, the plant is grown throughout the country from Andaman and Nicobar islands to the Himalayas up to 1800 meters above the sea level (1). It is also abundantly found in Malaysia, Australia, West Africa and some of the Arab countries. Ocimum sanctum (Linn) is the most prominent species of the genera. The leaves of the plant are considered to be very holy and often form a consistent part of the Hindu spiritual rituals ( Tirtha or Prasada ) (3). Ocimum sanctum has two varieties i.e. black ( Krishna Tulsi ) and green ( Rama Tulsi ), their chemical constituents are similar (4). Both the varieties also have common medicinal properties (3). Several medicinal properties have been attributed to the plant not only in Ayurveda and Siddha but also in Greek, Roman and Unani system of medicines (5). Traditionally,