The eighteen incompatibilities and nineteen antagonisms
The eighteen incompatibilities, shi ba fan, are the pairs of substances that Chinese medicine forbids in a single prescription because together they produce toxicity or a violent action: three base herbs, Gan Cao, liquorice root; Wu Tou, aconite; and Li Lu, veratrum root, each with the herbs it clashes with. The nineteen antagonisms, shi jiu wei, are pairs that weaken or distort each other's action and are avoided. Both descend from the seven relations of combination (qi qing) of the Shennong Bencao Jing, in which mutual incompatibility (xiang fan) and mutual antagonism (xiang wei) are two. The rhymed list of eighteen is credited to Zhang Zihe, of the Jin dynasty; the rhyme of the nineteen to the Ming physician Liu Chun. The Chinese Pharmacopoeia carries both under the heading of substances not to be used together.
The eighteen incompatibilities
Gan Cao, Glycyrrhizae Radix, is incompatible with: Gan Sui, Kansui Radix; Da Ji, both Jing Da Ji, Euphorbiae pekinensis Radix, and Hong Da Ji, Knoxiae Radix; Yuan Hua, Genkwa Flos; and Hai Zao, Sargassum.
Wu Tou, aconite, which means Chuan Wu, Aconiti Radix; Cao Wu, Aconiti kusnezoffii Radix; and Fu Zi, the processed lateral root, is incompatible with: Ban Xia, Pinelliae Rhizoma; Gua Lou, Trichosanthis Fructus, with its peel Gua Lou Pi, its seed Gua Lou Ren, and its root Tian Hua Fen; Bei Mu, both Chuan Bei Mu and Zhe Bei Mu, Fritillaria bulb; Bai Lian, Ampelopsis Radix; and Bai Ji, Bletillae Rhizoma.
Li Lu, Veratri nigri Radix et Rhizoma, is incompatible with: Ren Shen, Ginseng Radix, and by modern extension Xi Yang Shen and Dang Shen; Sha Shen, both Nan Sha Shen, Adenophorae Radix, and Bei Sha Shen, Glehniae Radix; Dan Shen, Salviae miltiorrhizae Radix; Xuan Shen, Scrophulariae Radix; Ku Shen, Sophorae flavescentis Radix; Xi Xin, Asari Radix; and Shao Yao, both Bai Shao and Chi Shao, peony root.
Counted by species and processed forms the modern list runs past eighteen; the number is the rhyme's. The classics hold a few deliberate exceptions: Zhang Zhongjing's Gan Sui Ban Xia Tang in the Jingui Yaolue pairs Gan Sui with Gan Cao, and Hai Zao Yu Hu Tang pairs Hai Zao with Gan Cao, to provoke a fierce action against a stubborn accumulation. In ordinary practice the pairs are never written together.
The nineteen antagonisms
Liu Huang, sulphur, antagonises Po Xiao, mirabilite. Shui Yin, mercury, antagonises Pi Shuang, arsenic. Lang Du, Euphorbiae fischerianae Radix, antagonises Mi Tuo Seng, litharge. Ba Dou, croton seed, antagonises Qian Niu Zi, Pharbitidis Semen. Ding Xiang, clove, antagonises Yu Jin, Curcumae Radix. Chuan Wu and Cao Wu, aconite, antagonise Xi Jiao, rhinoceros horn, now replaced in every prescription by Shui Niu Jiao, water buffalo horn. Ya Xiao, refined mirabilite, antagonises San Leng, Sparganii Rhizoma. Guan Gui, cinnamon bark, antagonises Chi Shi Zhi, halloysite. Ren Shen antagonises Wu Ling Zhi, flying squirrel faeces. The nineteen are the substances in these nine pairs.
Pregnancy
The materia medica divides its pregnancy prohibitions into the forbidden and the cautioned. Forbidden: the harsh purgatives and water-expellers Ba Dou, Qian Niu Zi, Gan Sui, Da Ji, Yuan Hua, and Shang Lu; the strong Blood-breakers San Leng, E Zhu, Shui Zhi, leech, and Meng Chong, tabanus; She Xiang, musk, which drives the foetus down; Ban Mao, mylabris; and the mineral poisons Xiong Huang, realgar, and Pi Shuang, arsenic. Cautioned, used only when the pattern demands: the Blood-movers Tao Ren, Hong Hua, Niu Xi, and Dan Shen; the downward-draining Da Huang, Mang Xiao, and Zhi Shi; the hot herbs Fu Zi, Rou Gui, and Gan Jiang; and Yi Yi Ren, coix seed, which is also a kitchen grain.
The toxic class and its processing
The Shennong Bencao Jing puts the toxic substances in its lowest class, to be used briefly and never for nourishment; the modern pharmacopoeia grades them as greatly toxic, toxic, and slightly toxic, and the processing (pao zhi) that makes them usable is not optional. Fu Zi is used only as Zhi Fu Zi, the processed slice, at 3 to 15 grams, decocted alone for 30 to 60 minutes before the other herbs are added, until a taste of the liquid no longer numbs the tongue; Zhi Chuan Wu and Zhi Cao Wu at 1.5 to 3 grams under the same rule. Ban Xia is used as Fa Ban Xia, Jiang Ban Xia, or Qing Ban Xia, and the raw rhizome only on the skin. Ma Qian Zi, nux vomica, is used sand-fried at 0.3 to 0.6 grams. Ba Dou is used as Ba Dou Shuang, the seed pressed free of its oil. Zhu Sha, cinnabar, and Xiong Huang, realgar, are levigated in water, never heated, and given in fractions of a gram, and outside China the mercury and arsenic minerals are mostly no longer dispensed.
The modern layer adds three rules. The Aristolochia herbs, Guan Mu Tong, Ma Dou Ling, Qing Mu Xiang, and their kin, were withdrawn after they caused kidney failure and urothelial cancer and are substituted in every old formula that named them. Ma Huang, ephedra, is restricted in many countries and is never combined with stimulant drugs or MAO inhibitors. Huang Lian, Wu Zhu Yu, and the other herbs that act on the liver's CYP enzymes change the blood levels of narrow-margin drugs such as cyclosporine, and are stated in a prescription alongside such drugs or left out.
Not medical advice.