Acetaminophen

Acetaminophen is one of the most widely used medicines for pain and fever. In many other countries it is called paracetamol. It is sold over the counter on its own, under brand names such as Tylenol and as store brands.

It is also an ingredient in many combination products, such as some cold and flu medicines, nighttime pain relievers, and prescription pain pills that pair it with an opioid.

People often take it for back and neck pain, and for years many guidelines recommended it as the first medicine to try for low back pain.

Even after more than a century of use, researchers do not fully understand how acetaminophen works. It seems to act mostly in the brain and spinal cord, where it turns down pain signals and lowers fever.

Unlike anti-inflammatory pain relievers (NSAIDs) such as ibuprofen and naproxen, it has only a weak effect on inflammation, the swelling and irritation in injured tissue. It barely affects platelets, the blood cells that help form clots, and it is usually easier on the stomach than NSAIDs.

Like other pain relievers, it does not change the cause of back or neck pain. The hope is to ease pain enough to keep moving while the body recovers.

Before you take it

Read the active ingredients on every medicine you use, including cold, flu and sleep products. Taking two products that both contain acetaminophen is a common way people take too much by accident. Prescription labels may shorten acetaminophen to APAP. It is in prescription pain pills that combine it with an opioid such as hydrocodone or oxycodone, and in many over-the-counter cold, flu, nighttime, and headache products. Formulas change, so read the label on each product.

Tell your clinician or pharmacist if you drink alcohol regularly, have liver disease, or take the blood thinner warfarin. If you are pregnant or planning a pregnancy, talk with your clinician before taking any pain medicine, including acetaminophen.

While you take it

The label lists how much to take, how often, and the most to take in a day. Follow it unless your clinician gives you different directions. Some people are advised to keep to a lower daily limit, such as people who drink alcohol regularly or have liver disease. Ask your clinician or pharmacist what limit fits you.

A simple note of what you take and when can help you stay within the limit, especially if you use more than one medicine.

Checking in

Check in with your clinician if your pain is not improving, or if you are taking a pain reliever on most days.

For new (acute) low back pain, high-quality studies show that acetaminophen works no better than a placebo (a dummy pill). [2] [3]

In the largest trial, more than 1,600 people with new low back pain took acetaminophen on a schedule, took it only when needed, or took a placebo for up to 4 weeks. All three groups recovered in about the same time, a little over 2 weeks. [8]

For long-lasting (chronic) low back pain, there is too little research to know whether it helps. Researchers found no trials of acetaminophen for neck pain, so its effect there is unknown. [2] [3]

Because of this research, the American College of Physicians’ 2017 back pain guideline does not include acetaminophen among the medicines it suggests. [15]

For hip and knee arthritis, it gives a small benefit that is probably too small for most people to notice. [3] [6]

Many people still use it because it can ease some other kinds of short-term pain, and it lowers fever. It is also gentle on the stomach, and it can be an option for some people who cannot safely take NSAIDs.

At label doses, most people have few or no side effects. In back pain trials, side effects were no more common than with a placebo. The main danger is taking too much, often by accident.

Less common

• Liver test changes. In studies where people took close to the daily maximum every day, abnormal liver blood tests were more common than with a placebo. What this means for long-term health is not clear.
• Heavy long-term use. Some observational studies link regular use at the high end of normal doses with stomach bleeding and with kidney and heart problems. These studies cannot show that acetaminophen caused them.
• Warfarin. Taking acetaminophen every day can make the blood thinner warfarin work more strongly, which raises the risk of bleeding. Your clinician may want to check your blood more often.

Rare but serious

Too much acetaminophen can cause severe liver damage, sometimes leading to liver failure, a liver transplant, or death. In a large US study of people treated for sudden liver failure at specialist liver centers, it was the most common cause.

About half of these cases happen by accident. They often involve people taking it for pain who use more than one product with acetaminophen, or who take more than the label says over several days. Regular drinking, liver disease, and not eating enough can raise the risk.

Very rarely, acetaminophen causes a severe skin reaction. Stop taking it and get medical help right away for a new rash, blisters, or peeling skin.

Other downsides

• For back pain, it often adds little, so check back with your clinician instead of continuing on your own for weeks.

Too much acetaminophen can harm the liver even when you feel fine at first. Early signs, if any, can be mild, like nausea or feeling unwell. If you think you or someone else took too much, call Poison Control at 1-800-222-1222 or get emergency care right away, even without symptoms. Treatment works best when started early.