"The Toxicity of Recreational Drugs" by Robert S. Gable explains: for any given drug, there's a dose that's usually lethal, and there's a dose that usually produces a high. How different these doses are, i.e., how much you have to mess up on your dosage to get into trouble, is a good gauge for how toxic the drug is. Booze is actually really bad by this measure; just ten times the effective dose is often a lethal dose. The DARE program I went through decades back talked a lot about the pot/booze/tobacco gateway-drug triumvirate without ever explicitly saying, "Thanks to historical contingency, two of these are legal but restricted, and one is THE DEVIL WEED." The more I find out about the three, the less I like the "one of these things is not like the other" aspect.

Alcohol thus ranks at the dangerous end of the toxicity spectrum.... Indeed, if alcohol were a newly formulated beverage, its high toxicity and addiction potential would surely prevent it from being marketed as a food or drug.

Check the chart. So the tiny 5:1 ratio of Median Lethal Dose to Median Effective Dose is one reason why heroin users are at such risk of dying by OD. And the psilocybin, LSD, and marijuana ratios are much safer:

The least physiologically toxic substances, those requiring 100 to 1,000 times the effective dose to cause death, include psilocybin mushrooms and marijuana, when ingested. I've found no published cases in the English language that document deaths from smoked marijuana, so the actual lethal dose is a mystery. My surmise is that smoking marijuana is more risky than eating it but still safer than getting drunk.

Probably the funniest phrase in the American Scientist article: a section header entitled "Other Ways to Invite Death."