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What is Tylenol?

Bottle and carton box of tylenol pills

Tylenol is a brand of over-the-counter (OTC) drugs marketed to both children and adults. Sold around the world, Tylenol products are pain-relief medicines with the active ingredient acetaminophen (also known as paracetamol). Acetaminophen is also available generically and appears as an ingredient in more than 600 medical products, including prescription medications. 

The history of Tylenol as a brand began in 1955 when McNeil Laboratories introduced Tylenol Elixir for Children. However, the history of acetaminophen goes back even further. In 1878, an American chemist named Harmon Northrop Morse first synthesized the chemical N-acetyl-p-aminophenol. The names “acetaminophen” (N-ACETyl-p-AMINOPHENol) and “Tylenol” (N-aceTYL-p-aminophENOL) both derive from the chemical name.

Today, the Tylenol brand is under the ownership of the pharmaceutical corporation Johnson & Johnson, though McNeil (now known as McNeil Consumer Healthcare) continues to manufacture the products. The Tylenol lineup now comprises 30 medical products, most of which are for cold and pain relief.

Tylenol uses

Tylenol and other acetaminophen products are in a class of medications known as analgesics and antipyretics. Analgesics are pain relievers, while antipyretics are agents that reduce fever. Thus, doctors and pharmacists commonly recommend Tylenol as a regular home remedy for common ailments such as headaches, backaches, and colds.

Tylenol’s flagship products consist of eight oral remedies designed to treat headaches and muscle pain. The brand also offers medicines for children and infants, along with products for targeting areas such as:

  • Sinus relief.
  • Sleep and pain.
  • Arthritis pain.
  • Cold and flu.

These products are available as tablets, chewable tablets, capsules, gel capsules, liquids, or dissolvable powders. They also come in a variety of strengths. Regular-strength products contain 325 milligrams of acetaminophen, while extra-strength products have 500 milligrams of acetaminophen. The brand’s eight-hour extended-relief medications provide the highest dose with 650 milligrams of acetaminophen.

Appropriate dosing of Tylenol depends on who is taking the product, what product they’re using, and how much acetaminophen the product contains. For adults:

  • Headache and muscle pain: Two regular-strength dose forms every four to six hours, two extra-strength dose forms every four to six hours, or two extended-relief dose forms every eight hours.
  • Sleep and pain: Two caplets or a 30-milliliter dose of liquid at bedtime.
  • Cold and flu: Two regular-strength caplets every four hours, two extra-strength caplets every six hours, or a 30-milliliter dose of liquid every four hours.
  • Sinus: Two caplets every four hours.

For children and infants, dosing depends on factors such as age and weight. Consumers can refer to the brand’s safety and dosing page to determine the correct doses related to these variables.

Generic acetaminophen serves the same analgesic and antipyretic function as Tylenol pain-relief products. For the same reason, it features in numerous other OTC medicines and some prescription medications, including:

  • Acetaminophen.
  • Alka-Seltzer.
  • Benadryl.
  • Coricidin.
  • DayQuil and NyQuil.
  • Dimetapp.
  • Excedrin.
  • FluTherapy.
  • Lortab.
  • Midol.
  • Mucinex.
  • Nyquil.
  • Panadol.
  • Percocet.
  • Robitussin.
  • Sinex.
  • Sudafed.
  • Theraflu.
  • Vicodin.

Often, the inclusion of acetaminophen helps to reduce symptoms associated with certain illnesses. For example, in the case of prescription pain medications like Percocet, medical providers may prescribe the two medications simultaneously to enhance the effects of the stronger pain-relief ingredient.

How Tylenol works

While experts understand that acetaminophen gets metabolized by the liver, they’re uncertain about the drug’s mechanism of action (how medicines work). Tylenol’s website states that acetaminophen may increase the body’s threshold for pain and help the body remove excess heat, but it doesn’t explain how.

That being said, researchers have studied acetaminophen for decades and developed several theories concerning its mechanism of action. One is that it blocks cyclooxygenase (COX) pathways in the central nervous system. COX is an enzyme that creates prostaglandin, a chemical that contributes to pain and fever when a person is sick or hurt. By hindering prostaglandin synthesis, acetaminophen may prevent the onset of these symptoms.

A second theory suggests that acetaminophen can activate the endocannabinoid system. The theory states that acetaminophen leads to the creation of a by-product called N-acylphenolamine (AM404), which creates a pain-relieving effect in both the brain and the spinal cord.

A third theory centers on serotonin, a chemical messenger in the central nervous system that can help regulate a person’s anxiety, improve their mood, and influence their pain threshold. Some research shows that acetaminophen use can increase serotonin in the brain, which in turn initiates the pain-relieving effects of the medicine.

Possible side effects of Tylenol

Different hands with pills

Tylenol, like all medicines, has side effects. Many are mild and do not appear on the product warning label, including:

  • Agitation.
  • Constipation.
  • Headaches.
  • Insomnia. 
  • Vomiting.

For most users, the mild side effects of Tylenol use are temporary. Should the symptoms last longer than a day, however, users should speak with their doctor or pharmacist.

In contrast, serious side effects may arise because of an allergy to acetaminophen, the symptoms of which may include:

  • Difficulty breathing.
  • Hives.
  • Swelling of the throat, tongue, lips, or face.

The United States Food and Drug Administration (FDA) has also warned of “rare but serious” skin reactions associated with acetaminophen, known as Stevens-Johnson syndrome, toxic epidermal necrolysis, or acute generalized exanthematous pustulosis. The symptoms of these conditions include:

  • Blisters.
  • Rash.
  • Reddening of the skin.
  • Skin detachment.

Skin reactions may occur at any time a person uses acetaminophen. Even previous users with no history of complications may experience them.

Issues associated with Tylenol

Though doctors and pharmacists commonly recommend Tylenol for pain relief, using acetaminophen may result in certain health complications.

Since the early 1990s, Tylenol has been the subject of numerous legal proceedings concerning its safety. The earliest lawsuits centered on the risk of liver damage and the development of dangerous skin reactions.

In more recent years, research has pointed to a possible link between acetaminophen and developmental disorders. Much of this research relates to acetaminophen use by pregnant women, potentially leading to the onset of autism spectrum disorder or attention-deficit hyperactivity disorder (ADHD) in their children.

Tylenol and liver failure

Liver failure is a serious complication of Tylenol overdose, which occurs when a user takes more than the recommended dose of acetaminophen. During an overdose, they undergo three to four distinct phases:

  • First 24 hours: In the first phase, the user experiences symptoms such as nausea, vomiting, and fatigue. They may also have unexplainable sweating and a lack of appetite.
  • 18-72 hours: The second phase largely affects the abdominal area. Symptoms at this time include cramping in addition to nausea and vomiting. Low blood pressure or an elevated heart rate is also common.
  • 72-96 hours: Here, the user begins to show signs of liver failure, such as jaundice (yellowing of the skin and eyes), bloody stools, and loss of brain function. Critical cases then proceed to multiple organ failure and, finally, death.
  • After 96 hours: Users who survive the overdose enter the recovery phase, in which their liver recovers. This phase can last up to three weeks.

Liver failure may also occur if users combine acetaminophen with alcohol, as both substances get metabolized in the liver. In 1994, a man named Antonio Benedi received $8.5 million in a lawsuit against McNeil Consumer Healthcare on the basis that the company failed to warn against this potentially fatal mixture. 

Hundreds of lawsuits concerning acetaminophen’s impact on the liver have arisen since the Benedi case, many of which did not involve alcohol. In 2007, for example, a 1-year-old child passed away from liver failure after taking a Tylenol product intended for infants. Also, in 2012, a woman experienced liver failure after several days of using Tylenol per the package directions.

To minimize the risk of liver failure, doctors, pharmacists, and other medical experts recommend taking no more than 4,000 milligrams of acetaminophen per 24 hours. For many people, a lower daily limit of 3,000 milligrams of acetaminophen may be safer.

Tylenol and developmental disorders

Since 2008, a growing body of research has suggested a link between acetaminophen use by pregnant women and developmental disorders in their children. Recent studies and reviews have shown that:

  • Acetaminophen can cross the placental barrier, a membrane that helps control the materials the fetus receives from the mother during pregnancy.
  • Acetaminophen affects the development of a child’s brain, increasing the risk of developing autism spectrum disorder, ADHD, or hyperkinetic disorders.
  • These disorders are dose-responsive, meaning that larger and longer doses typically increase the risk.

In 2015, the FDA released a communication warning consumers of these risks.

In 2021, a group of 91 medical experts, including doctors and scientists, released a statement in the journal Nature Review Endocrinology. In it, they reiterated the risk and expressed their consensus that:

  • Acetaminophen may not be appropriate for women at the beginning of pregnancy. 
  • Pregnant women should consult with a doctor or pharmacist to determine whether to take acetaminophen.
  • Pregnant women who use acetaminophen should minimize their doses and dosing period.

Then, in 2022, a number of Tylenol autism lawsuits began to arise against major retailers of acetaminophen. The plaintiffs claimed these retailers knew or should have known about the potential link between the drug and developmental disorders, but that they failed to warn consumers. In October, the Tylenol autism lawsuits became consolidated as a multidistrict litigation in the Southern District of New York. Additional lawsuits in November named Johnson & Johnson as a defendant as well.

Other issues associated with Tylenol

Medical experts also warn about other health risks associated with the long-term use of acetaminophen. In 2015, Dr. Philip Conaghan of the Leeds Institute of Rheumatic and Musculoskeletal Medicine led a systematic review of studies about acetaminophen. His team found that heavy or prolonged use of the pain reliever may lead to serious health concerns, such as:

  • Digestive tract bleeding.
  • Heart attack.
  • Hypertension.
  • Kidney disease.
  • Stroke.

According to one of the studies they examined, such use could even increase the risk of early death by up to 60%. As in the studies related to developmental disorders, the risks seem to be dose-responsive.