I can go you one better, LOL. 100 % of heroin users once drank milk.
That joke being out of the way, I know people who have used marijuana medicinally (MS patients) and they didn't "go on" to heroin, they, in fact, didn't go on to oxycontin, or percocet, or vicodin.
The marijuana controlled their pain and spasticity, so they used less drugs, not more.
You seem to be saying that human behavior cannot be predicted by rat behavior. Scientific heresy!