Acetaminophen is only effective at relieving pain and fever, while ibuprofen relieves inflammation in addition to pain and fever.

Other key differences:

• Some research suggests NSAIDs such as ibuprofen are more effective than acetaminophen at relieving pain.
• Ibuprofen is a NSAID so is not suitable for everybody and can cause gastrointestinal (GI) adverse effects, cardiovascular adverse effects, and kidney toxicity. This risk is low if no more than 1200mg of ibuprofen is taken per day.
• Acetaminophen appears to have more adverse effects than traditionally thought, and this risk increases with higher dosages. Any medication used for pain relief should be taken at the lowest effective dose for the shortest possible time.
• Either acetaminophen or ibuprofen may be used for headaches, fever and minor aches and pains, but ibuprofen is more effective for strains or sprains.

Acetaminophen brand names include Tylenol, Aceta, Apra and Mapap. Unlike NSAIDs, such as ibuprofen, it does not reduce inflammation. Experts aren't sure exactly how acetaminophen works but believe it affects COX enzymes in the brain, reducing the formation of prostaglandins (prostaglandins are substances released during injury that cause pain and inflammation). Even though acetaminophen works on COX enzymes, it is not considered a NSAID. Acetaminophen may be called paracetamol in some countries.

Ibuprofen is a type of NSAID that relieves pain. fever and also inflammation. Ibuprofen blocks COX enzymes, but to a different extent than acetaminophen. It is considered a nonselective NSAID because it blocks both COX-2 enzymes (involved in pain signaling and inflammation) and COX-1 enzymes (associated with a protective effect on stomach lining). This makes it effective at relieving pain and reducing inflammation, but there is a risk of stomach-related side effects. Brands of ibuprofen available in the U.S. include Advil, Genpril, Midol IB, Motrin IB, and Proprinal.

See also: Drugs.com Compare Tool - Acetaminophen vs Ibuprofen

Which one works for longer?

Acetaminophen and ibuprofen both work for a similar length of time

Acetaminophen is short acting with a relatively quick onset of action. Pain-relieving effects last for three to four hours; however, it is important acetaminophen is not taken more often than every four to six hours, and the maximum of 4000mg (4 grams) per day (24 hours) is not exceeded. In some cases (see below) a lower maximum dose (3000mg/day) should not be exceeded.

Ibuprofen is a short-acting NSAID, with a relatively quick onset of action. Pain-relieving effects last for approximately four hours. Like acetaminophen, it is better suited for the treatment of acute pain. Ibuprofen tablets/capsules can be given every four to six hours. If you are taking ibuprofen over-the-counter, the maximum recommended daily dose is 1200mg. Do not take more ibuprofen than recommended without consulting your doctor.

Which one is more effective?

Acetaminophen controls pain and fever but does not control inflammation so for conditions such as muscle sprains and cramps, ibuprofen will be more effective. One review showed that acetaminophen had little benefit in the management of osteoarthritis.

Risk of side effects

Acetaminophen has traditionally been considered relatively free of side effects; however, a 2015 review questioned that assumption and concluded that dosages at the upper end of the recommended dosing range were associated with NSAID-like adverse effects (such as an increased risk of heart attack and stroke, gastrointestinal (GI) ulcers and bleeding, and detrimental effects on the kidney). Use of acetaminophen for more than 13 weeks is also associated with a fall in hemoglobin (the oxygen-carrying component of blood), similar to that observed with ibuprofen. Experts still consider acetaminophen a safer option than NSAIDs for older or frail adults, as long as dosages given are at the lower end of the recommended dosage range. Acetaminophen appears to have a narrower window of safety compared to ibuprofen, and people taking acetaminophen should be warned that higher dosages may irreversibly damage the liver.

All NSAIDS are associated with a risk of GI, cardiovascular, and kidney adverse effects, some more than others. Ibuprofen is less likely than many other NSAIDs to cause GI side effects because it is short-acting. Low-dose ibuprofen (in dosages up to 1200mg per day) has a low risk of causing adverse cardiovascular events such as a heart attack or stroke. However, higher dosages of ibuprofen (up to the recommended maximum of 2400mg/day) are more likely to cause these effects. People who have already had a heart attack or stroke should talk to their doctor before using NSAIDs. One study showed that even one or two doses of ibuprofen or diclofenac (another NSAID) increased the risk of another cardiovascular event in those with a preexisting risk. NSAIDS should also not be used after coronary artery bypass graft (CABG) surgery. NSAIDs have also been associated with allergic-type reactions and can interact with other medications including angiotensin converting enzyme (ACE) inhibitors, angiotensin-II receptor blockers (ARBs), diuretics, clopidogrel, warfarin, dabigatran, and aspirin.

The 2015 study cited above also found that the risk of hospitalization for GI adverse events was significantly increased when acetaminophen and NSAIDs such as ibuprofen were combined. However, many experts still consider it safe to take acetaminophen and ibuprofen together for short periods of time (such as a couple of days) provided recommended dosages are not exceeded. To reduce the risk of side effects, it may be better to do alternate dosing, for example, acetaminophen at 8.00am, ibuprofen at 12 noon, acetaminophen at 4pm, ibuprofen at 8pm).

How to take them safely

• For acetaminophen, the generally recommended maximum daily dose for the average healthy adult is no more than 4000mg (4 grams) a day, from any source (acetaminophen is also contained in many combination cold and flu remedies, and in combination opioids such as Vicodin and Percocet). However, in some people, dosages close to 4000 mg/day could still be toxic to the liver. Consider erring on the side of caution, particularly if you are small or frail in stature, and take no more than 3000 mg/day.
• Do not assume that each brand of acetaminophen or ibuprofen contains the same dosage of a drug or has the same dosing instructions. For example, regular strength Tylenol contains 325mg acetaminophen per tablet and extra strength Tylenol contains 500mg acetaminophen per tablet. The maximum dose for extra strength Tylenol is 6 pills per day (3000 mg/day) and extra strength Tylenol should not be taken more often than every 6 hours.
• Don't drink too much alcohol (no more than 2 standard drinks/day for men and one drink per day for women) if you are taking acetaminophen as this can cause the liver to convert more acetaminophen into toxic byproducts. If you are taking any other medicines, check with your doctor or pharmacist before taking acetaminophen.
• When taking ibuprofen, take only the lowest possible dose for the shortest possible time (total daily dose should not exceed 1200mg).
• Do not take any other NSAID-containing products while being treated with ibuprofen, such as naproxen. Do not double up on acetaminophen-containing products.
• In people with pre-existing heart disease or who have suffered a heart attack or stroke, ibuprofen should be used with caution and only under a doctor's supervision.
• Older patients, patients with type 2 diabetes or with a history of stomach ulcers, kidney problems or at risk for heart disease are more likely to suffer from NSAID-related complications such as GI side effects, cardiovascular events, and kidney toxicity. Ibuprofen should be avoided unless your doctor recommends it and is monitoring you.