Aspirin vs. Acetaminophen

Instructor: Artem Cheprasov

Artem has a doctor of veterinary medicine degree.

This lesson is going to go over a wide variety of differences between aspirin and acetaminophen. You'll learn about some of the major differences with respect to side effects, their classifications, and much more.

Aspirin vs. Acetaminophen

You've almost certainly taken one or the other, or both. If you've had joint pain, you may have reached for some aspirin, and if you've had a fever, you may have used acetaminophen. Some of the uses of these two medications are similar, yet they are nonetheless different drugs. Let's find out some of the many differences these drugs have in this lesson.

Fundamental Differences


First of all, both terms, aspirin and acetaminophen are generic names. Aspirin probably rings a bell because even in brand name products, the term aspirin is usually used, as per Bayer Aspirin. However, the same can't be said about acetaminophen, where brand name products don't use the term in their names. Perhaps the best known acetaminophen-based product in the U.S. is Tylenol.


Both of these drugs can be classified in more than one way. Aspirin can be thought of as an NSAID or non-steroidal anti-inflammatory drug, an antiplatelet medication, an antipyretic, which is a fever reducer, as well as a non-narcotic analgesic, a non-opioid based pain reliever.

Acetaminophen is often classified as a non-narcotic analgesic as well and as an antipyretic. It is not an NSAID, nor does it have any therapeutic blood thinning effects like aspirin!


When taken orally, acetaminophen is absorbed just a bit from the stomach and is mainly absorbed in the small intestine. Contrast this with aspirin, which can be readily absorbed in both the stomach and small intestine under the right conditions.

Onset and Duration of Action

When taken orally, acetaminophen starts working in less than an hour and its analgesic effects last roughly 5 hours.

Aspirin's effects also last around 5 hours, with one important exception. Its antiplatelet effects last the entire lifetime of the platelet. In other words, around 10 days. This is important to remember if you ever have to give any other blood-thinning medication to a patient who was recently on aspirin.

There is also one other important consideration with respect to aspirin. This time, it's aspirin's onset of action. If a person takes a nonenteric-coated aspirin pill, then platelet inhibition will begin within an hour. However, if a person were to chew a nonenteric-coated tablet instead, then platelet inhibition will begin within 20 minutes. This is good to remember when a patient requires a rapid onset of action to aspirin, such as during a heart attack. Chewing enteric-coated tablets during such an event, when nonenteric-coated tablets aren't available, is a viable alternative.

Specific Considerations


Both of these medications are contraindicated (not advised) if a patient has a known hypersensitivity (allergy) to it or any other ingredients in the medication's formulations. However, there are some different contraindications they do not share.

For example, aspirin shouldn't be used in children or teenagers who have viral infections (regardless of whether they have a fever or not). This is because the child risks getting what's known as Reye's syndrome, which involves swelling of the liver and brain.

Adverse Effects

While both these medications can lead to similar adverse effects, such as nausea, there are some important differences. Aspirin is far more likely to lead to gastrointestinal ulceration. In fact, this happens between 6%-31% of the time. Aspirin is also more likely to lead to unexpected bleeding in general when compared to acetaminophen.


With respect to pregnancy, it should be noted that acetaminophen does cross the placenta and thus into the fetus. However, it is generally considered that using acetaminophen during pregnancy does not significantly endanger the unborn child. This is said, of course, with respect to a pregnant woman taking the medication only as directed by a physician. This is why acetaminophen carries a pregnancy risk category of B. However, it should be noted that overdosing on acetaminophen does increase the risk of miscarriage or stillbirth.

Contrast this with aspirin, which carries a higher pregnancy risk category of D. Aspirin can also cross the placenta and it may potentially lead to bleeding abnormalities and toxicity to the fetus, not to mention death. However, low-dose therapy as determined by a physician may be safe and appropriate under some circumstances.

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