Which of the following is NOT a side effect of nitroglycerin?

Tachycardia is not considered a typical side effect of nitroglycerin. Instead, nitroglycerin is primarily used to relieve chest pain (angina) by dilating blood vessels, which generally leads to a reduction in blood pressure. As a result of this vasodilation, the body often compensates by increasing heart rate in the attempt to maintain adequate blood flow and pressure. However, tachycardia itself is not a direct side effect of the medication; it's rather a compensatory response that might occur when blood pressure drops due to vasodilation.

In contrast, dizziness, burning under the tongue, and a drop in blood pressure are all common side effects associated with nitroglycerin. Dizziness can occur due to the lowered blood pressure that results from the medication. The sensation of burning under the tongue is a physiological response to the sublingual administration of nitroglycerin, as it is absorbed directly into the bloodstream through the mucous membranes. Lastly, the drop in blood pressure is a direct effect of the vasodilatory action of nitroglycerin, which can lead to symptoms of hypotension.