High Antihistamine Levels May Impair Fitness Progress, Research Reveals

Recent research from the University of Oregon highlights an intriguing connection between antihistamine medication and exercise adaptation. While antihistamines like Claritin and Zyrtec are commonly used to alleviate allergy symptoms by blocking histamine, their high-dose use during physical activity appears to hinder gains in aerobic fitness.

Histamine is a versatile signaling molecule that plays a crucial role beyond allergic reactions—involved in stress response and tissue adaptation. During exercise, histamine facilitates increased blood flow to muscles, promotes beneficial inflammation necessary for muscle repair, and activates genes that support recovery and growth. These processes collectively contribute to improved physical fitness.

The study involved 16 participants who engaged in a six-week cycling program, training three to four times weekly. Participants received either antihistamine medication or a placebo before each session. Results showed the placebo group experienced approximately double the improvement in cycling performance and blood flow compared to the antihistamine group. Interestingly, no significant difference was observed in maximum oxygen consumption (VO2 max) between the groups, possibly due to the study’s duration or sample size.

Histamine release originates from mast cells in skeletal muscles during activity, where it leads to blood vessel dilation and immune responses facilitating muscle remodeling. Blocking histamine appears to disrupt these critical adaptive mechanisms, reducing the effectiveness of endurance training.

While the study utilized higher-than-typical antihistamine doses, it raises questions about the impact of lower, everyday doses—such as those taken for seasonal allergies—on fitness development. Further research is necessary to determine if standard allergy medications could interfere with training results.

Overall, these findings suggest that antihistamine use, especially at high doses, might compromise the body’s ability to adapt to aerobic exercise. Athletes and individuals aiming to optimize fitness should consider the possible effects of antihistamines on their training progress.

Source: https://medicalxpress.com/news/2025-06-high-antihistamine-drugs-gains.html