Using hallucinogens for political and domination reasons, something common in some societies; the first idea that came to my mind was: “villagers are cheaper (10 less food) but have 5 less HP”, it could be a good initial economic boost but at the same time vulnerable to raiding.
The use of hallucinogens was common in Andean civilizations for religious purposes, but this is the first time I read that they were used in state parties for political purposes so this could be useful.
off-topic:
It reminded me of the Berserk, historically they used hallucinogenic plants before combat to release an angry frenzy. It would have been great to take advantage of that historical data but I guess when the game was designed in 1998 there was not the technology to use that data and they opted to give them health regeneration. It would be interesting if in the future a UU is added that has an energy bar like the Coustilliers that have the effect of temporarily increasing the speed of their attack.
As a curious fact in the Andean countries that had Inca influence, it was common for soldiers before entering combat to drink some type of “concoction” that supposedly increased their performance in combat, my father, who was a designated soldier on the border in the conflict of the 80’s, he mentioned to me that it was common to give soldiers a “concoction” containing gunpowder; ancient traditions I suppose. (I always relate this to the Starcraft Stimpack 
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