6 Antihistamine Side Effects You Should Know

Bad reaction? Here’s how to choose your allergy medication wisely.

- Sarah Jacoby

Like most allergy sufferers, I rely on medication to manage my symptoms. But antihistamine side effects – some of which may be unexpected – can make the experience as unique as the individual who’s taking them. Of course, all meds come with the risk of some side effects, and even with those side effects, the benefits of taking medication may still be worth it. But it’s always better not to be surprised by them.

How do they work? By targeting the body’s histamine-production system, which generates many of the symptoms we think of as ‘allergies’. Usually, when you expose your body to an allergen that you’re sensitive to – tree pollen, cat dander or dust, as an example – it erroneously interprets that substance as a threat and your immune system responds to combat it. This happens when the proteins in an allergen bind to IgE antibodies on the surface of mast cells, which causes the cell to release histamine, says Dr Charles Joseph Lane, a board-certified allergist. That histamine goes on to bind to histamine receptors, which then sets off reactions such as a runny nose, watery eyes, and other classic allergy symptoms.