Many people have a love-hate relationship with spring. The winter cold is finally melting into warmer weather, but along with higher temperatures comes pollen, and with the irritating yellow powder comes allergies. Those struggling with the seasonal symptoms can squelch puffy eyes and skin rashes by taking antihistamines — an easy choice, since they reduce the unnecessary immune activity, and the worst listed side effect is a bit of drowsiness. Researchers have uncovered another possible consequence of the drug, however, and it may be killing your workout game.

A team from the University of Oregon believes that high doses of antihistamines can blunt gene responses responsible for helping muscles recover after vigorous exercise, potentially causing problems. Back in 2005, Professor John R. Halliwill discovered that histamines, in addition to their known immunological duties, also relax blood vessels and increase blood flow during post-exercise recovery. He also found a link between the overactivation of certain histamine receptors and drops in blood pressure.

In the new study, led by doctoral student Steven A. Romero, the team expanded this research by looking at genetic activity. The researchers sequenced RNA, molecules crucial for protein synthesis and signaling between genes, to get a good look at exactly how histamine changed the body after exercise.

“We were looking for pathways associated with the growth of new blood vessels,” said Halliwill in a statement. “We saw evidence of that, but we also saw gene expression associated with glucose uptake by muscles, restructuring of muscle in response to exercise, immune responses, and intracellular communications.”

After an intense workout, about 3,000 genes work hard to aid recovery by giving muscles and blood vessels a boost. To determine histamine’s role in this, the researchers gave 10 physically active participants 540 milligrams of fexofenadine and 300 milligrams of ranitidine — both antihistamines that target one of the two known histamine receptors involved in recovery responses. The doses, though, were nearly three times what is recommended for over-the-counter histamines.

Researchers took biopsy samples from the quadriceps of all participants before, immediately after, and three hours after the subjects worked out for an hour. Before exercise, the antihistamines had no effect, and immediately after the workout their influence was still very low. Three hours after the workout, however, 795 genes usually involved in muscle recovery responded with lower levels of expression.

“Histamine, a substance that we typically think of negatively and is most often associated with seasonal allergies, is an important substance contributing to the normal day-to-day response to exercise in humans,” said Romero, who is now on a postdoctoral fellowship at the University of Texas Southwestern Medical Center.

The authors noted that the study only looked at a small portion of the genes involved in pathways influenced by histamine receptor activation.

“Our data really highlight that there remain many unanswered questions regarding the use of exercise to promote beneficial adaptations in humans,” Romero said. “Integrative physiologists from across the world have spent a great deal of effort conducting elegant studies in humans and yet we still have much work to do.”

Halliwill added that it is too early to say whether it’s a bad idea to take antihistamines before exercise.

“We need to do a training study in which we put people on histamine blockers and see if their adaptations to exercise training are as robust or diminished.”

Source: Romero S, Hocker A, Mangum J, Lutterell M, Turnbull D, Struck A, et al. Evidence of a Broad Histamine Footprint on the Human Exercise Transcriptome. The Journal of Physiology. 2016.