Before the Song Dynasty, the main processing method of Pinelliae Rhizoma was soup washing. The "new method" in Taiping Huimin Heji JuFang is a processing method that concocted with Ginger,white alum and starter-making.The "Fa Banxia" in the Yuan Dynasty's Yuyuan Yaofang comes from the Taiping Huimin Heji JuFang, and the Fa Wen Banxia, Fa Bai Banxia, and Fa Hong Banxia are the processing methods of patent medicine with a variety of other herbs.Fa Banxia appeared in the Ming Dynasty, and its auxiliary materials were ginger and white alum, and medical formulary began to include formulas containing Fa Banxia. Bencao Gangmu abbreviates the Yuan Dynasty's Fabai Banxia as "Fa Banxia", and is elaborated under the item attached "prescription" item instead of the "treatment". In the literature of Materia Medica, it is recorded that the preparation of auxiliary materials in Fa Banxia increased, including lime, licorice, soap horn, and simple nitro.After Daoguang in the Qing Dynasty, the Fa Banxia in famous medical cases was more used, and at that time, Fa Banxia was Xian Banxia. There are two recipes for Xian Banxia: one is made with seven processes, and the other is soaked in alum licorice water. During the Republican period, Zhang Cigong also pointed out that Fa Banxia was sliced Xian Banxia after rinsing and boiling, while the preparation method of Xian Banxia was Banxia made of ginger and white alum.Ye Juquan pointed out that the so-called "fa" is neither an ancient method nor a new method, questioning the process of repeated immersion in Banxia. After 1949, the questioning of Fa Banxia continued unceasing.Influenced by this, the 1960 edition Beijing Traditional Chinese Medicine Slice Cutting Experience included the method of soaking alum, licorice ,lime water, and was included in the 1963 edition of the Pharmacopoeia of the People's Republic of China.The 1985 version reduced the soaking time and eliminated the soaking process of alum based on the 1963 version, and this method is still used today.
宋代以前半夏的炮制方法主要是汤洗，《太平惠民和剂局方》新法半夏汤的“新法”，是半夏用姜制、矾浸、制曲等区别于汤洗的炮制方法。元代《御药院方》收载“法制半夏”的依据是《太平惠民和剂局方》，收载的法制温半夏、法制白半夏、法制红半夏是添加多种药物的成药制法。明代始有法半夏之名，其炮制辅料为生姜与白矾，方书开始收载含有法半夏的方剂。《本草纲目》将元代的法制白半夏简称为“法制半夏”，在“附方”项而非“修治”项下阐述，可见仍将其视为中成药。本草文献中记载法半夏的炮制辅料增多，包括石灰、甘草、皂角、朴硝等。清代道光以后，名家医案中的法半夏应用较多，当时法半夏即是仙半夏。仙半夏有两种配方：一种是用七道工序炮制者，一种是矾水甘草水浸泡者。民国时期章次公亦指出法半夏是仙半夏经漂洗煮制后切片，而仙半夏的炮制方法为半夏用生姜白矾制。叶橘泉指出所谓“法”字，既非古法亦非新法，对半夏反复浸泡的工艺提出质疑。1949年后，医界同仁对法半夏的质疑仍未停止。受此影响，1960年出版《北京市中药饮片切制经验》收载了白矾甘草石灰水浸泡的方法，并被1963年出版《中华人民共和国药典》收载；1985年出版《中华人民共和国药典》收载了该法减少浸泡时间并去除白矾浸泡的工序，并沿用至今。.