Tylenol Overdose or Poisoning

In Chicago in the fall of 1982, Tylenol (acetaminophen) capsules were found to be laced with cyanide, which proved quickly fatal in seven unwitting victims. To this day, law enforcement has yet to catch the person or people responsible for this heinous act.

The Chicago Tylenol murders not only claimed the lives of seven people but also nearly destroyed McNeil Consumer Products, a subsidiary of behemoth drug manufacturer Johnson & Johnson and the maker of Tylenol.

In what is now routinely used as a crisis management case study, at the height of the Tylenol panic, McNeil Consumer Products issued mass public warnings and recalled all existing Tylenol bottles, 31 million in total. McNeil Consumer Products also assured the public that all tampering occurred outside the factory.

In the weeks following Chicago Tylenol murders, Johnson & Johnson went from dominating the over-the-counter (OTC) analgesic market with 35% market share to a mere 8% market share. But within a year of the crisis, Tylenol rebounded after a $100 million investment in price reductions, tamper-proof packaging, and the introduction of a gelatin-coated caplet that was both easier to swallow and harder to interfere with.

During the crisis and over the years since, in the hearts and minds of the public, Tylenol has engendered enduring good faith as a safe, affordable, and effective pain reliever.

However, for reasons besides the now remote threat of criminal tampering, Tylenol can be dangerous. Few people probably consider that when taken in excess, acetaminophen can cause fatal liver failure. After all, bottles of acetaminophen look innocuous on medicine cabinet or store shelves. Fortunately, the repercussions of acetaminophen poisoning can be averted if an antidote is administered within the first eight hours of poisoning.

Understanding Tylenol

In the body, Tylenol enters circulation through the gastrointestinal tract. When taken correctly, it can be effective. However, Tylenol overdose is one of the most common poisonings, and it can be deadly if taken in large doses.

It takes about 30 minutes for the analgesic (pain-relieving) and antipyretic (fever-breaking) properties of this medication to take effect, and, under normal circumstances, our bodies clear about half a dose of Tylenol 2.5 hours after ingestion (this is also known as the half-life of the drug).

When taken for pain in adults, Tylenol is dosed between 500 milligrams and 1,000 milligrams every four to six hours. Current guidelines note the maximum daily dose is 4 grams (equal to 4,000 milligrams) of Tylenol a day. Some Tylenol caplets contain as much as 500 milligrams of acetaminophen, so you should never take more than two extra strength caplets every six hours or six caplets in 24 hours. Consult with your physician if you have a painful condition that requires you to take four caplets of Tylenol a day.

When taken in therapeutic amounts, most Tylenol is safely broken down by the liver through the metabolic processes of sulfation and glucuronidation. Furthermore, a smaller amount of ingested Tylenol (less than 5%) is directly excreted via the kidneys. Finally, with therapeutic dosages, a very small percentage is oxidized by the cytochrome P-450 system reactive metabolite N-acetyl-p-benzoquinoneimine (NAPQI); NAPQ1 is quickly detoxified by hepatic glutathione to a nontoxic acetaminophen-mercapturate compound, which is also eliminated by the kidneys.

In cases of Tylenol poisoning, the liver enzyme cytochrome P-450 is quickly overwhelmed, and stores of glutathione run out. Consequently, the reactive metabolite, NAPQ1, damages and kills liver cells, thus leading to liver failure.

Twenty-eight people died of Tylenol poisoning secondary to combined preparations, and 107 people died because of Tylenol alone. These statistics underlie an important clinical truth about Tylenol poisoning: Some people end up overdosing on acetaminophen because it appears benign (not harmful), but nearly equal numbers of people end up accidentally poisoning themselves because they fail to realize that Tylenol was also in other medications that they were taking.

Acetaminophen is found in more than 600 different OTC and prescription medicines. The following common drugs—analgesics, sleep medicines, and cold and flu therapies—contain acetaminophen:

• Lorcet
• Norco
• NyQuil
• Percocet
• Vicodin
• Darvocet
• Excedrin ES
• Unisom Dual Relief Formula
• Lorcet
• Tylox
• Vicks Formula 44-D
• Tylenol PM
• Sominex 2

To make matters worse, the adverse effects of many of these medications presented in combination with acetaminophen may initially mask the symptoms of Tylenol poisoning itself. This masking may lead to a life-threatening delay in treatment.

Tylenol poisoning can be divided into four stages, but not everyone will experience these four stages (especially those who ingested several doses of acetaminophen over time):

• Stage 1: During the first 24 hours, symptoms are nonspecific and include malaise (general feeling of discomfort or illness), anorexia (lack or loss of appetite), nausea, and vomiting. For unknown reasons, a poisoned person may develop hypokalemia or low levels of potassium in the blood, as well.
• Stage 2: At day two or three, once initial symptoms have waned, liver damage may set in, with symptoms including liver pain and tenderness and elevated liver enzymes (serum transaminases). Even without treatment, most people with mild to moderate liver poisoning (hepatoxicity) recover without consequence and don't enter Stage 3.
• Stage 3: By day three or four, fulminant hepatic failure takes place and may lead to encephalopathy (brain dysfunction), jaundice (bilirubin buildup causing yellow skin and whites of the eyes), coagulopathy (inability to clot blood), metabolic acidosis (too much acid in the body), and hypoglycemia (glucose deficiency). Gastrointestinal problems reappear, such as nausea/vomiting and anorexia. This is the stage in which there is the greatest risk of death.
• Stage 4: For those who survive Stage 3, recovery begins at about two weeks with the restoration of liver function at two months.

Moreover, people who are taking epilepsy or tuberculosis medications are also at greater risk because these medicines induce cytochrome P-450 enzymatic activity.

Treatment

Physicians treat Tylenol overdose based on protocols that have had high success in the past, including a widely used single acute acetaminophen overdose nomogram, a special type of diagram.

The antidote for Tylenol overdose is a drug called N-acetylcysteine (NAC). The efficacy of NAC highly depends on the time of treatment, and it's most effective if administered within 8–10 hours of acute single ingestion overdose. 

There are two options available: a 20-hour intravenous regimen and a 72-hour oral regimen. Oral administration of NAC has a foul odor but may be mixed with juice or other flavorings to make it taste better. If oral administration of NAC is not possible, then it will be administered intravenously. NAC is generally given for 20–72 hours.

Within one to two hours of an overdose, activated charcoal also can be administered to help absorb some of the acetaminophen. In the unfortunate case that acetaminophen has already damaged the liver, and fulminant hepatic failure has set in, a liver transplant may be needed.

Because signs of acetaminophen toxicity are generalized, it's imperative that you inform all your healthcare providers that you took too much Tylenol. (Emergency room physicians typically screen urine for Tylenol levels, but it's still important to communicate the events that led up to your feeling unwell.)

A Word From Verywell

Even though Tylenol and Tylenol-containing products appear harmless, they aren't. Before you pop another pill, stop and think about why you're taking Tylenol or other OTC analgesics and pain remedies. If you have to take acetaminophen, it is important to take only one medicine at a time that contains acetaminophen.

If your pain extends for some time, you need to seek medical attention. Please keep in mind that Tylenol won't heal chronic conditions like migraines or lower back injuries.

And be sure to check out Know Your Dose, an organization in partnership with the Acetaminophen Awareness Coalition to educate consumers on how to safely use medicines that contain acetaminophen.