What is NOT a primary effect of antihistamines?

Antihistamines primarily work by blocking the effects of histamine, a substance in the body that plays a crucial role in allergic reactions. By inhibiting histamine from binding to its receptors, antihistamines effectively reduce allergic symptoms such as sneezing, itching, and runny nose. They can also induce drowsiness, particularly the first-generation antihistamines, which have sedative effects due to their ability to cross the blood-brain barrier and affect the central nervous system.

In the context of this question, lowering blood pressure is not a primary effect of antihistamines. While some medications may influence blood pressure indirectly in certain circumstances, antihistamines do not primarily serve this function and should not be relied upon for blood pressure management. Therefore, this option stands out as not being a primary effect associated with antihistamine use.