ANSWER ----- YES
Although, by definition, no one was writing anything down (it's called pre-recorded history for a reason), and thus exact details are sketchy and much is speculation.
However, there is agreement by the vast majority of experts, in their respected fields, that the earliest known surviving Afro-Eurasian medical texts, whether ancient Egyptian papyrus scrolls, Mesopotamian clay tablets, Chinese tables etc. All of them speak of its use in the past tense, as if Cannabis had already been in medical use long before finding its way onto the written form. And some of these texts (at least the Sumerians ones) go back some 5000 years or more. Additionally, it should be noted that NOT one ancient text (anywhere) has been found that makes any reference to the recent discovery of Cannabis or of its medical properties**.
Thus it is with some safety that one can state that YES, medical cannabis was well in use before recorded history.
OUR THANKS TO the endiotane galleries of Swaziland.
-- Try as we could, we were not able to obtain permission to reproduce an actual copy of pre-historic Cave art. Our thanks to Courtesy of Endlotane galleries [http:www.endlotane.net] [An art gallery that specializes in Swaziland Cave Art reproductions] for allowing us permission.
[**] Actually this statement is not entirely accurate, the Greeks and Romans were experimenting with new uses for it, but even in there time, it was already well known for its medical properties.