Which of the following symptoms would most likely indicate a side effect of nitrates?

Nitrates are commonly used as antianginal agents to relieve angina by dilating blood vessels, which can lead to a number of side effects due to their vasodilatory effects. One of the most frequently reported side effects of nitrates is headache. This occurs because the expansion of blood vessels can lead to increased pressure and distention of intracranial blood vessels, resulting in a headache.

Patients often experience this side effect when they first start treatment with nitrates or when the dosage is increased. It is usually not severe and may diminish as the body adjusts to the medication.

In contrast, while dry mouth, weight gain, and rash may occur with various medications or conditions, they are not typical side effects associated with nitrates. Dry mouth is more commonly linked to other classes of drugs, weight gain is not a known reaction to nitrates, and while rashes can occur with many medications, they are not characteristic of nitrate therapy.