In general, states Zysk, Buddhist medical texts are closer to Sushruta than to Caraka, and in his study suggests that the Sushruta Samhita probably underwent a "Hinduization process" around the end of 1st millennium BCE and the early centuries of the common era after the Hindu orthodox identity had formed. Clifford states that the influence was probably mutual, with Buddhist medical practice in its ancient tradition prohibited outside of the Buddhist monastic order by a precedent set by Buddha, and Buddhist text praise Buddha instead of Hindu gods in their prelude. The mutual influence between the medical traditions between the various Indian religions, the history of the layers of the Suśruta-saṃhitā remains unclear, a large and difficult research problem.