Studies in humans and animals have found that certain antihistamines may affect testicular function in males.
A review of research on the topic, published in the journal Reproduction, found that in animal studies, antihistamines were likely to affect the production of male sex hormones in the testes. This could lead to altered morphology and decreased motility of sperm, as well as a lower sperm count.
'The average sperm quality in the population has been reducing over the last few decades, so it is always important to consider that common (and increasingly used) medications may be partly responsible,' said Dr Channa Jayasena, senior clinical lecturer at Imperial College London and a member of the Society for Endocrinology, who was not involved in the study.
However, only certain classes of antihistamines may harm male fertility, the review found. Those that could cause changes in testicular activity were not the commonly used over-the-counter medications often used to treat allergies, noted Dr Richard Quinton, senior lecturer in endocrinology at Newcastle University, who was not involved in the study. These are H1-blockers, which were not linked to the potentially harmful testicular effects.
'In relation to drug effects in humans, the concerns only really arise in relation to the H2 blockers (and one in particular - Cimetidine),' Dr Quinton said. 'The findings of this paper aren't likely to be relevant to the antihistamines we take for allergies, even though it's a great paper overall.'
Much of the research reviewed in the study was in animals such as mice, rats and bulls. There is so far a lack of studies to see if the same effects apply in humans, the review noted.
'For now, I see no reason why men who need to use anti-histamines should not continue to do so,' said Allan Pacey, professor of andrology at the University of Sheffield, who was not involved in the study.
Darren Griffin, professor of genetics at the University of Kent, who also was not involved, added: 'Persistent sneezing is not a particularly good reproductive strategy either so perhaps taking the antihistamines, when necessary, is the lesser of two evils.'
Histamine is a chemical released in the body as a response to an infection. In people with allergies, the body mistakes something harmless, such as pollen, for a threat and consequently releases histamine, leading to an onset of symptoms such as, rashes, runny nose and sneezing.
Antihistamines stop histamine affecting the cells in the body, which reduces allergy symptoms. They have also been shown to prevent motion sickness and as a short-term treatment for insomnia.
The study authors concluded that the review was a first step to understanding how certain antihistamines may affect human fertility.
'The data compiled in this review indicates the crucial involvement of histamine in orchestrating testicular functions, but even so there is still much to learn about the implicated mechanisms,' said Dr Carolina Mondillo from the Institute of Experimental Biology and Medicine in Argentina and a study author.