The active principle in Salvia divinorum is salvinorin A, a trans-neoclarodane diterpenoid.
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O \\___/ H_\____
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--- H \____/_CH3 \
O-\ / |
Salvinorin A is active in humans at 200-500 micrograms, and is thus many times more potent than any other plant-based hallucinogen. Doses of 1000mg/kg in mice did not produce fatalities (this is 5000 times the effective dose for humans!)
Salvinorin A may be extracted from fresh or dried leaves [...]