Although researchers were quick to point out that the findings from this study are preliminary and do not show that antihistamines cause brain tumors, there appears to be a link between the use of such medications and an increased risk of developing certain brain cancers.
Clearly, since so many people use antihistamines for things like sneezing, itching, dry mouth, hay fever, other allergy-related symptoms, Â the incidence of brain tumors would be significantly higher if these drugs actually caused the cancers.
What is apparent, however, is that prior studies have indicated that people with allergies or asthma have a lower risk of glioblastoma, the most deadly variety of brain tumor.
The theory is that allergies and asthma may be responsible for producing sufficient inflammation in the brain to keep immune system cells active and working to prevent these cancers.
Thus, the team was curious to see if  the use of antihistamines to eliminate allergy-related symtoms might also negate the protective effect the allergies produce.
According to the researchers, glioblastomas account for up to 50% to 60% of the new (about 17,000) U.S. cases of brain cancers each year and kill some 17,000 others. What actually causes these cancers remains largely a mystery, however.
The team was surprised to find that, while the use of antihistamines had no effect on the risk of developing glioblastomas, they were associated with of other types of brain tumors.
For example, antihistamine users were 2.8 times more likely to develop lesser-grade anaplastic astrocytoma brain tumors and 86% more likely to develop low-grade glioma brain tumors than non-users.
Though both of these types of tumors are “low-grade,†these low-risk brain forms of tumors are often deadly as well.
The data also reconfirmed the prior findings that anti-inflammatory drugs and chickenpox confer protection against glioblastoma. It appears that once a person has had chickenpox, the virus remains dormant in the brain forever. As a result, the team believes that the latent virus continues to cause the low levels of inflammation associated with the development of a “variety†of cancers.
The study used data from two other studies in which participants were asked about their use of antihistamines and anti-inflammatory drugs. Â The final group that was analyzed included 610 people with brain tumors and 831 people without cancer.
Experts stress that people who use antihistamines should not stop taking the drugs if and when they need them. While the data shows that the inflammatory process is involved in the development of cancer, it does not indicate that drugs themselves cause cancer.
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