March 21, 2000 (Cleveland) -- Acetaminophen, the active ingredient in painkillers such as Tylenol, may worsen breathing difficulties in people with asthma and may make it more likely for anyone to develop symptoms of asthma, according to a new study. Researchers found that daily users of the painkiller were more than twice as likely to have an asthma attack as people who did not take the drug at all.
Current guidelines from a national asthma education program recommend that asthma patients use Tylenol instead of aspirin because in some people with asthma, aspirin can cause difficulty breathing, says Anthony Temple, MD, vice president for medical affairs for MacNeil Consumer Products. MacNeil is the maker of the Tylenol brand of acetaminophen. He says it is likely that Tylenol use is high among asthmatics and that he knows of no other study linking use of the painkiller to worsening asthma.
The researchers looked at more than 1,500 people with and without asthma. In the British study, asthmatics who took paracetamol -- the equivalent of acetaminophen in England -- every day were likely to have more severe asthma than asthmatics who rarely took the painkiller. The study is reported in the March issue of the journal Thorax.
Researcher Jonathan A.C. Sterne, PhD, tells WebMD that the more paracetamol the study participants took, the worse their asthma got. In spite of previous known associations between aspirin and asthma, these researchers did not see any worsening of asthma among those who took aspirin regularly. Sterne is senior lecturer in medical statistics at the University of Bristol in England.
Among the people with asthma at the beginning of the study, Sterne and colleagues found that frequent users of paracetamol had more severe asthma attacks.
Sterne says that people who took paracetamol weekly were 80% more likely to have asthma than people who never used paracetamol. People who used the painkiller daily were twice as likely to have asthma, he says. The researchers also found that paracetamol was associated with increased nasal congestion but aspirin was not.
Sterne, who worked at Guy's, King's and St. Thomas's School of Medicine in London when the study was conducted, says it is too early to make recommendations based on these findings. He says that asthmatics are "cautioned to avoid aspirin" so it is likely that they would be more frequent users of acetaminophen. "But we don't think anyone is in the position to advise against using paracetamol at this point," Sterne says. This study is the first to report an association between acetaminophen and worsening asthma, he says, and "these findings need to be confirmed" before clinical recommendations can be issued.
"We think the findings should be interpreted with very much caution. We are concerned that there are some inherent flaws in the study, but I'm not prepared to elaborate at this time," says Temple. One possible flaw, he says, is that the study doesn't show that acetaminophen causes worsening asthma, it just shows "an association" between acetaminophen use and worsening asthma.
The authors speculate that frequent paracetamol use may deplete the lung of an antioxidant called glutathione. Researchers think glutathione, which is found in the lining of airways, may play an important role in preventing damage to the lungs.
People with asthma are especially susceptible to airway damage due to substances such as pollutants and smoke, so depleting the body's natural protection against them could, theoretically, worsen asthma symptoms. In laboratory studies and in animal studies, paracetamol has been shown to decrease glutathione. But more studies are needed to determine what effect paracetamol has on glutathione in humans, says Sterne.
So right now, the best advice for people with asthma who are daily users of Tylenol is to try to cut back, Sterne says.
- British researchers report that patients taking England's equivalent form of acetaminophen had more trouble with their asthma symptoms. Also, taking the painkiller, which is commonly sold as Tylenol in this country, makes it more likely anyone could begin to have asthma symptoms.
- The vice president of medical affairs at Tylenol's manufacturer counters that national asthma guidelines promote the use of Tylenol over aspirin, as aspirin could make breathing more difficult in some asthma patients. He added he did not know of any other study linking Tylenol and problems with asthma.
- The authors of this study did not find that aspirin worsened the symptoms of asthma patients. They recommend asthma patients cut back on their use of Tylenol if they use it daily.