Of the drugs that Americans routinely abuse, many of them are quite toxic. Take a look at this:
The median lethal doses for different substances in a 100kg male:
nicotine 5 g
Cocaine 9.5 g
aspirin 20 g
THC (main ingredient of marijuana) 127g
alcohol: 180 g
caffeine 192 g
acetaminophen (Tylenol): 200 g
table salt: 300 g
Sucrose (table sugar): 2900 g
The issue here is not so much the total lethal dose, but how close you must be to the lethal dose in order to get the effect you are looking for. The largest cluster of substances has a lethal dose that is 10 to 20 times the effective dose: These include cocaine, MDMA (often called "ecstasy") and alcohol. A less toxic group of substances, requiring 20 to 80 times the effective dose to cause death, include Rohypnol (flunitrazepam or "roofies") and mescaline (peyote cactus). 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 that document deaths from smoked marijuana, so the actual lethal dose is a mystery. My guess is that smoking marijuana is more risky than eating it, but still safer than alcohol.
Alcohol ranks at the dangerous end of the toxicity spectrum. So despite the fact that about 75 percent of all adults in the United States enjoy an occasional drink, it must be remembered that alcohol is toxic. This makes me wonder why we spend so much money on the drug war. Nevermind, the answer is profit.