The four characters denote an over-all property of the Chinese medicines, i.e., cold, hot, warm and cool. In general, cold and cool as well as hot and warm are of the similar property but of various degrees. That is to say , a cool drug is slightly cold while a hot one is extremely warm. In addition, there are some medicines which are neither cool nor warm and are said to be " neutral". In fact, although the character of " neutral" drugs is not so evident, yet they trend to be sightly cool or slightly warm. So they are not classified as a special character.
The four characters of Chinese medicines are determined by their therapeutic effects on various disease. For instance, for cases with heat-syndrome manifested as fever, thirst, flushed face, conjunctivitis and rapid pulse, Gypsum Fibrosum(石膏）, Rhizoma Anemarrhenae（知母）, etc （such as White Tiger Decoction）are effective and they are considered as cool and cold in nature. While for cases with cold-syndrome manifested as chilliness, cold limbs, pale complexion and slow pulse, Radix Aconiti Lateralis Praeparata (制附子），and dried Rhizoma Zingiberis (干姜）etc, (such as Decoction for Yang Exhaustion) are effective, hence they are considered as warm and hot in nature. Applying medicines of different characters in line with syndrome differentiation is the key of clinical practice in traditional Chinese medicine.