Bencao yanyi 本草衍義, also called Bencao guangyi 本草廣義 "Extension of the pharmacopoeia", is a book on drugs of various character written by the Song period 宋 (960-1279) scholar Kou Zongshi 寇宗奭 (early 12th cent.), who was a small official in the prefecture of Lizhou 澧州. The book is 20-juan long and was finished in 1116.
Kou was of the opinion that correct treatment was only possible by personal diagonsis and the correct understanding of how drugs were effective. For this reasons, he studies the most important writings on drugs and compiled an own manual. The first three juan are a broad and systematic introduction (Xuli 序例) into the topic in which Kou admonishes the practitioner to avoid errors in diagnosis and therapy. The main text, consisting of seventeen juan, comments on 460 specific drugs of materia medica, mainly the Jiayou buzhu Shennong bencao 嘉祐補注神農本草 (short Jiayou bencao 嘉祐本草), a commentary on the ancient pharmacopoeia Shennong bencao 神農本草 compiled during the mid-11th century, and the illustrated Bencao tujing 本草圖經 from the 7th century (part of Xinxiu bencao 新修本草).
Kou's commentary adds new findings on quite a range of drugs, mainly on the right methods to discern between useful and harmful indication by the study of earlier observations in the field of clinical medicine. Kou described habitat and appearance of each drug, its place of origin, methods of collecting and preparation, character and taste, as well as its application and effects. The focal point of each description is how to discern (jianbie 鑒別) particular drugs from similar ones. In quite a few cases, Kou corrected errors of earlier writings. The book was therefore praised by the great Ming period 明 (1368-1644) master Li Shizhen 李時珍 (1518-1593), author of the famous Bencao gangmu 本草綱目 and the Qing period 清 (1644-1911) master Yang Shoujing 楊守敬 (1839-1915).
Nonetheless, the book also includes some erratic statements, as Kou was influenced by the then-popular theory of the circulation of breath (yunqixue 運氣學). In his introduction, Kou discussed the traditional belief in the "four breaths" (siqi 四氣, i.e. cold, heat, warm, and frigid 寒熱溫涼), which he renamed "four characters" (sixing 四性) of a disease. He also introduced the "eight necessities" (bayao 八要) in diagnosis, meaning that a physician had to check the "void" (xu 虛), the "replenished" (shi 實), cold (leng 冷) and heat (re 熱), the abnormal (xie 邪), the correct (zheng 正), as well as the inner (nei 內) and the outer (wai 外) appearance of the patient.
The book was first printed in 1185 by the Transport Commission of Jiangxi 江西轉運司; a revision was published in 1195; it was also circulating as an appendix to the compendium Daguan bencao 大觀本草. The text served as a primary source for the Yuan period 元 (1279-1368) medical encyclopaedia Zhenglei bencao 類證本草. In 1877, Lu Xinyuan 陸心源 from Gui'an 歸安 included the text in his reprint series Shiwanjuanlou congshu 十萬卷樓叢書. Modern editions were published in 1957 by the Commercial Press (Shangwu yinshuguan 商務印書館) and in 1990 (commented edition) by the People's Medical Publishing House (Renmin weisheng chubanshe 人民衛生出版社).