Do antihistamines lose their effectiveness over time?

Contrary to popular belief, antihistamines do not cause either habituation or loss of effectiveness over time.

However, some individuals may experience a decrease in their effects, a phenomenon that can be explained by various factors.

• An increased exposure to allergens.

  One of the main causes of an apparent decrease in the effectiveness of antihistamines is related to the increase in exposure to allergens in the environment. Certain periods conducive to allergies, such as windy summer weeks when pollens are abundant in the air, can intensify exposure to allergens and overload the immune system. The production of histamine in the body then becomes too significant for antihistamines to continue to function correctly and effectively block symptoms. This situation is not a loss of drug effectiveness, but an imbalance between the amount of allergens released and the treatment. In this case, it is advisable to adapt one's allergy management, for example, by avoiding drying laundry outside and closing windows during the day.

• An evolution of allergy.

  Allergies can evolve over time, and many individuals develop poly-sensitization, which is an increased reactivity to several different allergens. Patients initially allergic to a single substance may become sensitive to other elements in their environment, thereby increasing the overall allergenic load. When exposed to these new substances, symptoms may appear despite the use of antihistamines. Indeed, this new sensitization intensifies the release of histamine, which becomes too significant for the antihistamines taken to act effectively. There is again an imbalance between the amount of histamine in the body and the medication, this time due to a change in the allergic profile.

• A non-allergic reaction.

  Pollution, tobacco smoke, or certain chemicals can cause symptoms similar to those experienced during an allergic reaction, even though they are not considered allergens. Indeed, unlike true allergens, these substances do not provoke the release of histamine. Therefore, antihistamines, which specifically block the effects of histamine, cannot alleviate these reactions. If a person perceives a decrease in the effectiveness of their antihistamine treatment without a clearly identified allergic cause, it is possible that other non-allergenic irritating factors are involved. In this case, taking antihistamines will not produce the expected effect and it will then be essential to identify the source of the irritation to stop the reaction.

If you feel that your antihistamines are not effective enough, do not hesitate to seek advice from your doctor, so they can guide you towards a more suitable treatment.