Recently saw the PBS documentary, "Story of India", and during one episode, they profile a drink in Afghanistan called Hom, which scholars speculate may be the drink, Soma, referred to in the Vedas. The main ingredient is ephedra, but it is sometimes also brewed with poppy and cannabis. The Vedas provide evidence that some sort of mind altering drink was consumed in religious contexts in ancient India. These substances are still used in India as medicines, so we can reasonably speculate that they have been used all along. (maybe someone with more knowledge of Indian medicine might be able to chime in).
It would not be surprising that such medicines were used widely in the Buddha's time. I know that even now, cannabis tea is used in the Caribbean for medicinal purposes by the square community. It would not be surprising that such medicinal uses would have been acceptable during the Buddha's time in India.
Intoxication is another matter.
This does not add up to evidence that the Buddha got stoned, and the overwhelming evidence is that getting stoned was not OK in the sangha. There is a big difference between taking a mild tea for an upset stomach and eating a pot brownie.
Tea is widely consumed by Buddhists... drink too much and you get intoxicated. Caffeine high is a high.
Those who, even with distracted minds,
Entered a stupa compound
And chanted but once, “Namo Buddhaya!”
Have certainly attained the path of the buddhas.
-Lotus Sutra, Expedient Means Chapter
I think each human being has things to find out in his own life that are inescapable. They’ll find them out the easy way or the hard way, or whatever.