Acetaminophen toxicity depends on the amount ingested, the period of time over which it was ingested, the state of the liver, the age of the patient, and a few other things.
A convenient rule of thumb is that a single dose over 140 mg/kg is a potentially toxic dose, but such a dose in a youngster with a normal liver would be readily tolerated and in an older individual with liver disease might be very problematic. Complicating the clinical picture is a tendency for an acute overdose to cause vomiting (making it difficult to predict how much actually got absorbed), or be associated with chronic or acute alcoholism, and so on.
One cannot simply throw a dose out there (especially with no body weights attached) and make a recommendation for what is safe.
In general it’s a reasonably safe drug. Proper evaluation of an acute overdose includes a blood level (more than one level sometimes, depending on the time of ingestion) and liver enzyme sets looking for serious damage. In the dozens of acetaminophen overdoses I’ve taken care of over the years, I’ve never lost a patient to it, although lots of them have had enough potential injury to require an antidote. I suspect there are many other ingestions that were high enough to cause some subclinical changes. Fortunately the liver heals well, on average.
500mg per 1 caplet is EXTRA strength acetaminophen. I believe “normal” Tylenol is half that. Get her to a doctor to get checked out, I’d say. I got griped out by my doctor for taking regular doses of extra strength acetaminophen (generic Tylenol) more than once a day for a decent stretch. (And admitted to sometimes taking a dose of 3 extra strength caplets.) She told me to stop it, and wanted me to never take it again for fear of my liver, or kidneys being damaged.
Ok, going to the Tylenol site, I see that “regular” Tylenol is 325mg per caplet. Still… Extra Strength Tylenol Click ingredients to confirm what I say on these links.
I was taking less than that, but I’ve had more than one kidney infection, so worry about liver damage, and kidney damage is the issue. You might still ask the doctor to be safe? Prolonged use of Tylenol also isn’t good, and is of concern, is why I am saying check in with the doctor to be sure it is still all ok.
Like I said, he’s probably being overly cautious (it is his nature), but I am also a regular social drinker, so he’s probably taking that into account, as well.