5:1 ratio (a dose is "take two 325mg") between therapeutic and danger doses is really low as far as modern drugs would be concerned. Most drugs are more in the 50:1 or 100:1 range, drugs with a 5:1 ratio typically would not be approved and certainly would require very close supervision. Tylenol being OTC is complete insanity (or rather, regulatory capture and general public comfort with it).

Also note that those dosages are only for single usages! Tylenol also has a fun thing where daily/chronic usage within the "safe" dose can still cause liver damage. Chronic usage, you need to halve those doses.

The causal mechanism is believed to be basically low-level liver damage. Drinking a sixpack of beer once every couple weeks is fine - it's still not healthy, it damages your body, but your liver will repair itself in the meantime - but do it every day and your body cumulatively cannot repair the damage, while drinking a ton could cause acute failure. Tylenol actually works the same way - every dose is damaging your liver a bit, but if you don't do it every day it's fine, your body will repair it. But if you do take it daily, your body doesn't get a chance to repair the liver damage that tylenol causes, and the actual "safe" dosage becomes lower.

That puts the actual "safe" dose at closer to 1500mg per day for an adult. Having a 2.5:1 theraputic ratio on an over-the-counter drug is absolute fucking insanity.

And worse, those numbers are for men - they're lower for women. Yes, so is the theraputic dose, but they don't make special pills for women. Taking a standard dose (two 325mg pills) twice a day can cause liver damage to women, that's above the safe threshold for daily/chronic use. And that's not something people really consider when they pop a couple tylenol.

And then you've got combination products. OK, so you get sick, you take a couple tylenol and a dose of cough syrup. The dose of cough syrup likely is another 500mg or so of tylenol. So you actually took a 1125mg dose. And then you do it again before you go to bed. That's edging into dangerous territory with tylenol.

Obviously "don't do that", read the label and don't double up on an active ingredient that's already there in combination, but combination products are implicitly dangerous, they are fishing for that to happen, encouraging it. But the FDA wants it because it "discourages abuse". That's literally more important than burning out your liver.

The rest of the world uses tylenol in very niche situations. Usually it's behind the counter at a minimum (not always, but usually) and you probably will be told to take some ibuprofen instead. Ibuprofen and Aspirin are not perfect but they are much, much, much safer than tylenol is.

Tylenol is absolutely, completely, absurdly dangerous and should not be anywhere near as common as it is in the US, but drug war + legacy product sales rule the day.

To echo another sibling commenter here, I don't allow acetaminophen in the house period. It is an accident waiting to happen. I certainly don't allow combination products, and I will actively go out of my way to buy anything that doesn't include it. This is overkill as a single childless person who is aware of the danger, but you never know when something could go wrong and the cat knocks the bottle off the counter and the dog gets it, etc. You just should not keep dangerous things around unless you absolutely need to. Some things you can't avoid, but it's not hard to just buy ibuprofen instead of tylenol.