Samhitas say that Ayurveda was not written by human beings.
“Brahma Smrutvayusho Vedam ……”,says Vaghbhat, meaning Bramha recalled Ayurveda.
Arundatta says the words – “Smartrutvam eva atra na kartrutvam”.(It was recalled, and not created), meaning, even Bramha didn’t create it . It was just recalled by him.
It is an Upa-Veda of Atharva Veda.
So, how did it reach us then?
It was given by Lord Indra to humans.
Why? Because a sage named Maharshi Bharadwaj went to him as a represantative of sages who were united at the foothills of Himalayas in a conference to solve the problem of increased prevalence of diseases in mankind.
Bharadwaj asked for help from Lord Indra, to relieve suffering humanity, and Lord Indra taught him Ayurveda as an answer. Bharadwaj was sent to Indra, because he volunteered to do so, as well as he was one of the brightest Sages present at that time.
After Bharadwaj returned, he gave his knowledge to all Sages present there. Out of them Punarvasu Atreya gave this knowledge to his 6 disciples. Agnivesh was his brightest student who wrote Agnivesh samhita which was later modified to be the oldest Ayurveda text which is still available, the Charaka Samhita.
Lord Indra had received the knowledge from Ashwinikumars, who received it from Daksha Prajapati, who in turn had received it from Bramha.