Which of the following is a common side effect of expectorants?

Expectorants are medications designed to help clear mucus from the respiratory tract by thinning and loosening phlegm. A common side effect associated with the use of expectorants is dry mouth. This occurs because some expectorants can reduce saliva production or result in mucosal dryness as they work to stimulate secretions in the airways.

In contrast, other side effects like constipation, blurred vision, or headache are not typically associated with the use of expectorants. Constipation is often linked to medications that cause a slowing of gut motility, blurred vision may relate to other medication classes affecting the eye, and headaches can arise from a variety of causes, including dehydration or tension, neither of which are directly tied to the effects of expectorants. Thus, dry mouth stands out as a recognized and common side effect of this category of medication.