Imagine a scale of mind-alteredness from 0 to 10, where 0 is stone-cold sober and 10 is a complete disconnection from reality.
At 0, your senses are passing along information to your brain completely normally, and it might be said you are perceiving the outside world naturally, in a way that allows you to function as a human adapted to its environment over millions of years. At 10, you might as well be sleepwalking or in a dream state: basically nothing from the outside world is getting effectively communicated to your brain, time appears to no longer exist, you may not even feel you have a body or an identity or any ties to the universe. Where do various doses of various substances get you on this scale? I’ll relate my own take on it:
I’ll start with alcohol, since I have experience with it and it has a fairly one-to-one relationship between number of drinks and where it gets me on the mind-alteredness scale. One drink (a “drink” is a 12oz 5%ABV beer, 2oz of 80-proof liquor, or a 6oz glass of wine) gets me to 1. I feel a bit more relaxed, maybe even get a very slight buzz if I haven’t eaten recently. Two or three drinks within an hour gets me to 2 or 3, which I’d call “tipsy.” 5 drinks in an hour and I’m drunk: obviously (even to myself) not safe to drive, fairly uninhibited in what I say or do, ideas seeming to flow quickly and easily. 7 drinks and the room is spinning when I go to bed and I’m definitely going to feel sick the next day; I very likely will throw up that same night. (I’ve been there only a handful of times in my life.) 10 drinks and I would be black-out drunk, probably close to toxic shock. (I’ve never actually done this, thank goodness.)
10 on the scale could also refer to the opaque depths of a heavy DMT trip or salvia experience. A shroom or acid trip typically maps to 8 or 9, especially if you experience hallucinations. Opiates (taken recreationally) seem to typically get people somewhere between 5 and 8. Caffeine is dosed and ingested such that it offers a lot of fine gradations between 0 and about 2, but you can’t usually take enough of it to get past that — it’ll kill you first.
Cannabis doesn’t seem to have any noticeable effects until you’re plopped down around a 3, where everything feels a little “off”. When people get high they are usually aiming at a 5 or 6: time slows down a lot, hidden qualities in things seem to pop out everywhere, and depending on the strain of cannabis ingested, motor coordination is impaired.
All this might constitute an argument for why all drugs can’t be legalized and taxed the way we do alcohol. Coming home from work and smoking a joint or even a one-hitter bowl isn’t the same, from an intoxication standpoint, as coming home and drinking a beer, even if a legal market in cannabis means more transparency and precision over how it’s dosed. Moderation in weed might always have more to do with how often you use it than with how high you get when you do. For other less-mainstream drugs the difference compared to alcohol is potentially even more dramatic.
Of course, this argument only holds is intoxicatedness is the heuristic by which the legality of a substance is determined; clearly it isn’t.