Which is NOT an adverse effect of Sumatriptan (Imitrex)?

• A. NAION
• B. Retinal artery occlusion
• C. Systemic Vasodilation
• D. Retinal venous thromboses

Answer: (C)

Sumatriptan acts by stimulating 5-HT1B/1D receptors on blood vessels, causing vasoconstriction of intracranial and retinal vessels. This tendency toward reduced blood flow explains adverse events that are related to vasospasm in the eye or heart, such as non-arteritic anterior ischemic optic neuropathy or retinal artery occlusion, and even rare retinal venous thrombosis reported in some cases. Since the drug promotes constriction rather than dilation, systemic vasodilation would not be expected as an adverse effect. So, systemic vasodilation is the option that does not fit with sumatriptan’s vasoconstrictive action.