Historical evolution and processing mechanism of 'nine steaming and nine drying' of traditional Chinese medicine preparation.

Context: Nine steaming and nine drying is a traditional Chinese medicine (TCM) processing method and it is widely used for processing tonifying herbs. Modern research reveals that the repeated steaming and drying process varies the composition and clinical efficacy of TCM.

Objective: This paper analyzes and explores the historical evolution, research progress, development strategies, and problems encountered in the nine steaming and nine drying process so as to provide a reasonable explanation for this method.

Methods: English and Chinese literature from 1986 to 2023 was collected from databases including Web of Science, PubMed, Elsevier, Chinese Pharmacopoeia 2020 (CP), and CNKI (Chinese). Nine steaming and nine drying, processing, TCM and pharmacological activity were used as the key words.

Results: Nine steaming and nine drying has undergone thousands of years of clinical practice. Under specific processing conditions of nine steaming and nine drying, the ingredients of the TCM have significant changes, which in turn altered clinical applications.

Conclusions: This review provides sufficient evidence to prove the rationality and scientific value of nine steaming and nine drying and puts forward a development direction for future research.