With the passage of time, as new knowledge accumulated, it looks, it was felt necessary that Agnivesha tantra should be revised. This was done by Charaka and the revised edition of Agnivesha tantra came to be called Charaka Samhita. During the ninth century, Charaka Samhita was again edited and reconstructed by a Kashmiri Pandit named Dridhabala, son of Kapilabala, a resident of Panchanadapura, now known as Panjor situated seven miles north of Srinagar. The present form which Charaka Samhita has, was given to it by Dridhabala. He not only added the missing chapters but also edited the whole samhita. 
Charaka Samhita deals elaborately with subjects such as foetal generation and development, anatomy of the human body, function and malfunction of the body depending upon the equilibrium or otherwise of the three humours of the body, viz., of vayu, pitta and kapha. It describes etiology, classification, pathology, diagnosis treatment of various diseases and the science of rejuvenation of the body. It discusses elaborately the etiology of diseases on the basis of the tridosa theory. It gives a detailed description of the various diseases including those of the eyes, the female genital organs, normal and abnormal deliveries and diseases of the children. Charaka's materia medica consists chiefly of vegetable products though animal and earthy products are also included in it. All these drugs are classified into 50 groups on the basis of their action on the body. 
This vast treatise also gives an idea of the various categories of the practitioners of the healing art, specialization in different medical subjects, physicians and their fees, nursing care, centers of medical learning, schools of philosophy such as Nyaya and Vaiseshika which formed the fundamental basis of medical theories, medical botany and classification of the animal kingdom, particularly in regard to properties of their flesh etc. It also describes various customs, tradition, legends, routine of daily life, habits of smoking and drinking, dress and clothing of the people of that era. 

Commentary on Charaka Samhita by Chakrapanidatta, called Charaka Tatparya-Tika or Ayurveda Dipika, done in the eleventh century (A.D. 1066), is very famous. 
Charaka Samhita was translated from Sanskrit into Arabic in the beginning of the eighth century and its name Sharaka Indianus occurs in the Latin translation of Avicenna, Razes, and Serapion, a translation of the Karka from Sanskrit into Persian and from Persian into Arabic is mentioned in the Fihrst (finished in A.D. 987). It is likewise mentioned by Alberuni. Charaka Samhita was first translated into English by A.C. Kaviratnain 1897. 
The life and times of Charaka are not known with certainty. Some Indian scholars have stated that Charaka of Charaka Samhita existed before Panini, the grammarian, who is said to have lived before the sixth century B. C. Another school argues that Patanjali wrote a commentary on the medical work of Charaka, which is corroborated by his commentator, Chakrapanidatta. They say that if Patanjali lived around 175 B.C., Charaka must have lived some time before him. Another source about the identity of Charaka and his times is provided by the French orientalist Sylvan Levi. He discovered in the Chinese translation of the Buddhist Tripitaka, a person named Charaka who was a court physician to the Indo-Scythian king Kanishka, who in all probability reigned in the second century A.D. From the above discussion, it would seem that Charaka may have lived between the second century B.C. to the second century A.D. Till such time as further and more conclusive evidence is available, to narrow down this period would not be justifiable.