Acetaminophen (“paracetamol” in Europe and brand name “Tylenol”) is an omnipresent force in pain relief at almost every level of healthcare.  It is inexpensive, readily available, and generally well-tolerated.  It is the most widely used medication in the world, and many medical societies list it as a first-line option to relieve suffering.  

Break your leg?  Tylenol.  

Have surgery?  Tylenol.  

Dental work?  Tylenol.  

Broken heart?  Not medical, but the resulting hangover may still be improved by Tylenol.  

Perhaps the most revealing evidence of acetaminophen’s benefit comes from a back-handed complement: comparison to opioid efficacy.  Although studies reveal some advantages in pain control for the first seven days of opioid use, its effectiveness diminishes afterwards to not exceed acetaminophen, and it is questionable if opioids are truly better in the acute phase. 

The “Miracle”

The story of acetaminophen’s development starts where many medical discoveries begin: a serendipitous accident by trainees.  In the 1880s, two medical residents at the University of Strassburg requested a medicine to help treat a patient’s intestinal worms.  A pharmacist accidentally brought a compound which helped bring down the patient’s fever but did nothing for the worms.  Analysis of the medicine identified a chemical called acetanilide, which was subsequently marketed as Antifebrin (cleverly meaning “against fevers”).  This drug also demonstrated pain-killing qualities, and pharmaceutical companies modified it several times to capitalize on this benefit.  For many years, an iteration called phenacetin was the preferred anti-fever and pain medication until experimentation showed its chemical component acetaminophen was really doing the work.  Acetaminophen hit the market in the 1950s and has been prolific since.   

For many years, we did not know exactly how acetaminophen worked.  Is it an anti-inflammatory like ibuprofen?  Does it interfere with nerve signaling like an anti-depressant?  Does it bind pain receptors like opioids or marijuana?  The answer, as stated so wryly in the Coen Brothers’ underappreciated film masterpiece Hail, Caesar! – “It’s…complicated.”  Acetaminophen seems to exhibit all these qualities, which may explain both its utility as a pain reliever and its range of potential side effects.  We are still gaining knowledge about its characteristics, including what it does best. 

The “Messiness”

A 2021 systematic review of systematic reviews (a study that groups together other groups of studies to synthesize as much data as possible) related the following findings:

1. Acetaminophen provides modest pain relief for knee and hip osteoarthritis.
2. Acetaminophen is not effective for acute (sudden and recent) low back pain.
3. Acetaminophen has about the same frequency of bad side effects as placebo, except for liver damage, which was more frequent at high, repeated doses. 

This last finding is interesting because the most recent research has focused on potential harms of acetaminophen, leading to a shift in perception regarding its safety.  Since it is processed in the liver, damage to this organ is common in cases of overdose.  Similarly, it should not be used in those with liver failure.  

A 2025 study looking at use in people over age 65 showed many of the same side effects as ibuprofen, including peptic ulcers, high blood pressure, and chronic kidney disease.  (Of note, the study did not define what dose of acetaminophen caused these side effects, making it difficult to know how much is safe.)

So where does this leave us?  I think of acetaminophen the same way I think of most over-the-counter medications.  We wouldn’t take them at high doses for long periods of time.  Almost every medication box directs “If symptoms persist beyond seven days, seek medical attention.”  The maximum dose of acetaminophen is 3000 mg in a 24-hour period.  Taking more than this or taking it longer than a week with poorly controlled pain probably means we should talk with a doctor about what is going on and how to make it better.  

Acetaminophen is a very useful medication, but it is not for everybody.  Some people metabolize it too quickly and render it ineffective, or they have medical conditions making its use unsafe.  That’s all right; there are other options.  Considering its availability, affordability, and established effectiveness, I am grateful we have such a medication in our pain-fighting arsenal.

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References:

1. Kaur J, Nakafero G, Abhishek A, Mallen C, Doherty M, Zhang W. Incidence of Side Effects Associated With Acetaminophen in People Aged 65 Years or More: A Prospective Cohort Study Using Data From the Clinical Practice Research Datalink. Arthritis Care Res (Hoboken). 2025 May;77(5):666-675.
2. Abdel Shaheed C, Ferreira GE, Dmitritchenko A, McLachlan AJ, Day RO, Saragiotto B, Lin C, Langendyk V, Stanaway F, Latimer J, Kamper S, McLachlan H, Ahedi H, Maher CG. The efficacy and safety of paracetamol for pain relief: an overview of systematic reviews. Med J Aust. 2021 Apr;214(7):324-331. 
3. Ayoub SS. Paracetamol (acetaminophen): A familiar drug with an unexplained mechanism of action. Temperature (Austin). 2021 Mar 16;8(4):351-371.