Acetaminophen is a popular pain reliever sold under the brand name Tylenol and around the world as paracetamol. A new analysis of research shows that it may not work as well as expected for some common conditions (BMJ, online, March 31, 2015).
Back Pain
Australian researchers conducted a meta-analysis of studies comparing acetaminophen to placebo for the treatment of back pain. They also examined studies comparing the drug to placebo treatment of osteoarthritis of the knee or hip.
The investigators did statistical analyses covering 13 clinical trials: 10 on osteoarthritis pain and 3 on lower back pain. The hip and knee arthritis trials included 3,541 patients. The trials for lower back pain included 1,825 subjects. The longest follow-up on any of these trials was six months, so it is not possible to draw any conclusions about acetaminophen over the long term.
What they found from these studies was discouraging, however. The scientists concluded:
“Paracetamol [acetaminophen] is ineffective in the treatment of low back pain and provides minimal short term benefit for people with osteoarthritis.”
They urge that recommendations to use this drug for lower back pain or arthritic knees and hips should be re-evaluated.
In other words, acetaminophen just doesn’t work as well as many health professionals and patients believe. It is often recommended as an alternative to NSAIDs for pain relief. That is because it is far less likely to damage the digestive tract than drugs like aspirin, diclofenac, ibuprofen, meloxicam or naproxen.
What Is the Effect on the Liver?
The Australians found no significant differences in patient-reported side effects between acetaminophen and placebo. They did find, however, that people on acetaminophen were four times more likely to have elevated liver enzymes, a red flag for liver damage.
For years the makers of Tylenol have emphasized the drug’s safety record. In ad campaigns, viewers were told, “Tylenol is the pain reliever hospitals use most. I can’t think of a better reason to trust Tylenol.” More recently the company has stressed that “Tylenol has been the #1 doctor recommended brand of pain reliever for over 20 years.”
But researchers have long known that high doses of acetaminophen can be toxic to the liver. An investigation by ProPublica in 2013 revealed that more than 1,500 people had died as a consequence of complications of acetaminophen use during the preceding decade. Most of these deaths were due to liver problems.
People who drink alcohol may be especially susceptible to liver injury if they also take acetaminophen.
Asthma & Other Problems
Acetaminophen use has also been linked to higher risk of asthma (Chest, Nov., 2009) and hearing loss (Otolaryngology–Head and Neck Surgery, March, 2015). Other side effects include elevated blood pressure, nausea, headache, rash, kidney damage, anemia and a potentially life-threatening allergic reaction called anaphylaxis.
Serious Skin Reactions
In 2013 the FDA warned about a new set of complications. Skin reactions called Stevens-Johnson syndrome, toxic epidermal necrolysis or acute generalized exanthematous pustulosis can occur at any time acetaminophen is taken. While rare, such adverse effects can be fatal.
Based on the latest meta-analysis, it is hard not to conclude that acetaminophen is less effective than most of us imagined. It also has more serious side effects than is generally appreciated.
