An estimated 50 million Americans have allergies and anywhere from 35 percent to 50 percent use antihistamines.
In a recent study of 867 U.S. adults, researchers at Yale University in New Haven, Connecticut, found that prescription antihistamine users were more likely to be overweight or obese than non-users.
Among the 268 antihistamine users, 45 percent were overweight, versus 30 percent of the 599 study participants not on the medications.
Researchers were interested in looking at the relationship between antihistamines and weight because of what's known about medications called atypical antipsychotics. Drugs, such as olanzapine (Zyprexa) and risperidone (Risperdal) are used to treat schizophrenia and other mental illnesses and carry the side effect of weight gain. They also have antihistamine effects.
Histamine is a chemical produced in the body that is best known for its role in promoting the inflammation associated with allergic responses. Blocking histamine is a good thing when it comes to relieving hay fever symptoms.
Cells throughout the brain have receptors for histamine and the chemical appears to play a role in a number of physiological functions. Appetite control and calorie burning are among them.
So in theory, antihistamines could contribute to overeating and slower fat breakdown.
On average, antihistamine users had a higher body mass index (BMI). That compared with a BMI of about 28 among non-users, which correlates to being moderately overweight. BMI is a standard measure of weight in relation to height used to gauge obesity.
When the researchers accounted for participants' age and sex, antihistamine use was linked to a 55 percent increase in the odds of being overweight versus non-use. The medications were not linked to higher odds of elevated blood sugar, insulin or cholesterol, however.
More studies are needed to see whether antihistamines do in fact have an effect on body weight.
Experts recommended that people with allergies talk with their doctors about all the potential side effects of the different treatment options and try to find one that works best for them.