Antihistamines, commonly available over the counter and used to treat allergies, may contribute to male infertility, according to the results of a new systematic review.

The authors of the new paper argue that more studies examining this link are required, and they suggest that people be warned about overusing these drugs.

Study co-author Dr. Carolina Mondillo and team are due to report their results in the journal Reproduction.

Histamine is a molecule that the body produces when the immune system is activated by a perceived threat.

Histamines attempt to remove allergens from the body by inducing sneezing, itching, or making the eyes water.

This is part of the standard defense system of the body—but in some people, the immune system overreacts to triggers, such as pollen, pet dander, or dust, and it prompts histamines to create excessive sneezing or eye-watering, as with hay fever.

Antihistamines are the most commonly used medicine for reducing these symptoms. However, as well as acting on histamine, antihistamines have also been found to affect other areas of health, creating unwanted side effects linked to sleep-wake behavior, sexual function, and fertility.

Because allergies are becoming increasingly common in industrialized countries, antihistamine use is also increasing, so it is important that scientists and doctors better understand any side effects tied to these over-the-counter drugs.

Antihistamines reduce sperm quality

The researchers, from the Instituto de Biologia y Medicina Experimental in Buenos Aires, Argentina, conducted a systematic review of animal studies that investigated associations between histamines and fertility. They looked at both small- and large-scale studies that had taken place over the past 4 decades.

The review found that several of the studies reported an association between antihistamine use in male animals and impaired function of the testicles.

The study authors suggest, then, that antihistamines seem to interfere with the production of sex hormones in the testicles, leading to misshapen sperm, poor-swimming sperm, or a low sperm count.

It is important to bear in mind that all of the studies that Dr. Mondillo and colleagues looked at were conducted in animals. Studies in humans looking at the association between antihistamine use and male fertility are limited, so it is difficult to generalize these findings to humans.

Further studies are now needed

Further research will also be needed before the mechanisms behind this association can be fully understood.

"More large-scale trials are needed to evaluate the possible negative effects of antihistamine on reproductive and sexual health," says Dr. Mondillo. "This can then lead to developing novel treatments to relieve allergy symptoms without compromising fertility."

The researchers say that they will now begin to evaluate how histamines impact testicular tumors.

In previous studies, some other common medicines have also been associated with male infertility, such as calcium channel blockers, tricyclic antidepressants, and anabolic steroids.