Millennia is plural. That was the problem. If it was one millennium it would be wrong by more grammatically correct.
Much better would have been 'for several millennia'. Bonobos and Chimps use lots of plants for medicinal reasons but some may also have psychoactive properties. In experiments chimps will prefer water laced with psychoactives. But then so will rats and mice.
Humans seem to have found pretty much every last psychoactive natural substance (nutmeg!). Mongolians bereft of fermentable grains fermented milk instead so ingrained is the human desire to get buzzed. There is some evidence that the drive to domesticate grains was at least initially driven by the desire to make a sour mash beer for celebrations/rites rather than feeding the multitudes.
The English have long looked down on us Scots for eating oats, but that is because we use the barley for making whisky and beer. Demand for high protein barley to ferment is so high in Scotland that in recent years English farmers have been growing the right barley varieties to sell here, under urging by the Scotch Whisky Industry.
Gin production (all those botanicals!) has transformed the economics of starting a whisky distillery. No longer do you have to wait three years for your spirit to be deemed to be whisky before you can cash in. Now you can make the whisky, put in casks to mature, then make some gin full of local botanicals (they must be local) and sell that while you wait. Even the gin is usually made from unpeated malted barley.
Oats are still a wonder food though. I partake regularly and ate nothing else until dinner time yesterday. Oats rule.