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Basic Facts about Acetaminophen

Updated on December 25, 2009

In today’s world, acetaminophen is a remarkably popular over-the-counter drug. Most commonly known as paracetamol in many countries, this drug is classified as an analgesic (pain reliever) and an antipyretic (fever-lowering drug). However, as with any other drug, you need to know exactly how acetaminophen works, when it is indicated, as well as how to avoid its side effects and toxicity.

Brief History of Acetaminophen

A derivative of coal tar, acetaminophen or paracetamol belongs to a class of drugs called “aniline analgesics”; and is the only drug known as such that’s still in use. It is in fact, the active metabolite of phenacetin, a well-known analgesic and antipyretic in the past; however, unlike phenacetin and its combinations, paracetamol is not known to cause cancer at therapeutic levels. The names paracetamol and acetaminophen are both derived from the chemical name of the compound para-acetylaminophenol. In certain contexts, this compound is simply called APAP, an abbreviation for N-acetyl-para-aminophenol. In this article, acetaminophen and paracetamol are used interchangeably, but since the title bears the name acetaminophen, this name will be used more often here than paracetamol.

In the United States, acetaminophen gained FDA approval in 1951 and was first distributed by Sterling-Winthrop Co. in 1953. The company promoted the drug as preferable to aspirin since children and people with ulcers could take it safely. Tylenol, the most popular acetaminophen brand in the U.S. was launched in 1955 by McNeil Laboratories which began to market acetaminophen under the brand name Tylenol Children’s Elixir, a pain and fever medication for children. Like acetaminophen and paracetamol, the word Tylenol also came from para-acetylaminophenol.

In 1956, Frederick Stearns & Co., a Sterling Drug Inc. subsidiary, produced 500 mg paracetamol tablets and marketed as Panadol in the United Kingdom. Panadol was initially a prescription drug for pain and fever relief, and was promoted as being “gentle to the stomach” unlike other analgesics available during that time. Paracetamol was incorporated to the British Pharmacopoeia in the year 1963, and has become very popular since then as a pain reliever with less side effects and little drug interaction with other pharmaceutical agents. But safety issues regarding paracetamol use prevented it from gaining widespread acceptance until the 1970s. Then in the 1980s, the sales of paracetamol went beyond those of aspirin in many countries, including the United Kingdom. This, together with the demise of phenacetin in the market due to analgesic nephropathy and hematological toxicity attributed to it, made paracetamol even more popular.

Since the expiry of paracetamol patent in the U.S. several years ago, many generic versions of the drug have emerged under the Drug Price Competition and Patent Term Restoration Act of 1984. However, certain preparations of Tylenol remained protected until 2007.

Facts about Acetaminophen

Mechanism of Action

Although it is not exactly known how acetaminophen works, experts believe that this drug alleviates pain by increasing the person’s pain threshold, the level by which the individual feels pain. When pain threshold is elevated, pain would have to be greater for a person to feel it.

As a fever-lowering agent (antipyretic), acetaminophen acts on the area of the brain that regulates body temperature. It particularly orders the brain’s thermoregulation center to lower the temperature when it is elevated.

Other Uses

Although primarily indicated for the relief of fever and mild aches and pains, acetaminophen can also be used to treat pain due to mild arthritis. However, since this drug does not have an antiinflammatrory action, it does not relieve any forms of inflammation, swelling and redness. But acetaminophen is as effective as aspirin in relieving pain that is not due to inflammation.

Available Preparations

Acetaminophen is an over-the-counter drug that comes in various forms. It is available as chewable tablets, coated caplets, gelcaps, geltabs, liquid suspensions, and even suppositories.

Interactions with other drugs

Since acetaminophen undergoes metabolism in the liver, drugs that enhance the action of liver enzymes that break down acetaminophen can therefore lower the therapeutic levels of the drug. This can in turn reduce the therapeutic effects of acetaminophen. Drugs known to increase the action of liver enzymes include carbamazepine (Tegretol), and antituberculosis drugs isoniazid (INH, Nydrazid, Laniazid) and rifampin (Rifamate, Rifadin, Rimactane). Acetaminophen doses greater than recommended amount can cause toxicity to the liver and may lead to severe liver damage. This potential toxic effect of this drug in the liver is heightened when combined with alcohol or drugs that are also harful to the liver.

The intestinal absorption of acetaminophen is reduced by cholestyramine (Questran). This can lower the effects of acetaminophen. To avoid this, acetaminophen must be given 3 to 4 hours after cholestyramine or an hour prior to cholestyramine administration.

Acetaminophen may also enhance the blood thinning action of warfarin (Coumadin), when daily doses exceed 2,275 mg. It is therefore imperative to avoid administration of large acetaminophen doses during the course of warfarin treatment.

Precautionary Considerations

Most drugs are not safe to be taken during pregnancy. But women in all stages of pregnancy can take acetaminophen safely. In fact, it is the treatment of choice for short-term fever and minor aches and pains during pregnancy.

The use of acetaminophen in nursing mothers appears to be safe too, although the drug is passed into the breast milk in small quantities.

Side effects of acetaminophen                                    

When used properly, acetaminophen rarely causes any side effect. However, this drug can cause liver damage when taken in excessive quantities. This serious adverse effect can also result when acetaminophen is used over a prolonged period, or simultaneously with alcohol or other drugs harmful to the liver. Chronic alcohol intake may further increase the risk of bleeding in the stomach.

Final Thoughts

Due to its efficacy in treating fever and minor pain; coupled with its safety in children and pregnant women, acetaminophen or paracetamol can be considered as one of the greatest discoveries in the field of medicine and pharmacology. And the convenience of getting it without prescription is indeed something to be appreciated. We simply ought to be responsible in its use to maximize the benefits while avoiding its harmful side effects.


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    • Melody Lagrimas profile image

      Melody Lagrimas 6 years ago from Philippines

      Hi, I guess acetaminophen in the US is mostly marketed in combination with other drugs. Tylenol, I think comes in pure acetaminophen and combination preparations as well. Those other brand names may not be available in the US in tablet forms. I am sorry, but the FDA website is your best source for such info.

      Hope this helps.

    • profile image

      Himanshu Garg 6 years ago

      Thanks for valuable recommendations.

      We are not able to find the registration status of these strengths on the US FDA website (Orange book). Is there any other listing of approved drugs in US. Please help clear as there is only one product on US FDA website i.e. Tylenol 650 mg extended release.

      Hope to receive your valuable suggestions.

    • Melody Lagrimas profile image

      Melody Lagrimas 6 years ago from Philippines

      Hi, maybe you can try Tylenol, Tempra, Mardol, Apacet, Feverall, Panex, Paramol, etc.

      Thanks for reading and commenting.

    • profile image

      Himanshu Garg 6 years ago


      Can you please suggest any tablets available in US market for Acetaminophen 500 or 250 or 125 or 160 or 80 mg.

      Thanks in advance

    • anglnwu profile image

      anglnwu 8 years ago

      Very informative, with interesting thorough research. I'm truly grateful for this medical invention--a miracle pill, to say the least. Great job!

    • Melody Lagrimas profile image

      Melody Lagrimas 8 years ago from Philippines

      James, glad that you find it very informative.

      healthgirl10, thanks for dropping by and for commenting too.

      Hi Peggy, thanks for your usual support. Yes, my daught is now feeling better, she'd been absent from school for a week.

      Ms Chievous, thanks for your comment and for sharing that too.

    • Ms Chievous profile image

      Tina 8 years ago from Wv

      Coal tar? Blech! You know, I have heard from attending stress management seminars that drinking a glass full of room temperature water can get rid of your headache just as well as a pill.

      Very well done hub!

    • Peggy W profile image

      Peggy Woods 8 years ago from Houston, Texas

      You do such great research when writing articles like this. I also did not know that it came from coal tar. Very interesting and well done, Melody.

    • Peggy W profile image

      Peggy Woods 8 years ago from Houston, Texas

      Is your daughter feeling better?

    • profile image

      healthgirl10 8 years ago

      Thanks for all the information about acetaminophen. I found it very intriguing as I'm very interested in all kinds of cold relief.

    • James A Watkins profile image

      James A Watkins 8 years ago from Chicago

      This is fascinating. I learned a lot from reading your article. Thanks for the illumination.

    • Melody Lagrimas profile image

      Melody Lagrimas 8 years ago from Philippines

      Thanks, Ethel and R burow for dropping by and for commenting.

    • R Burow profile image

      R Burow 8 years ago from Florida, United States

      I had no idea acetaminophen is a derivative of coal tar.

    • ethel smith profile image

      Eileen Kersey 8 years ago from Kingston-Upon-Hull

      The humble wonder.


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