**Question:** The WRONG statement of sumatriptan is that it -

A. does not act specifically on the serotonin receptors
B. does not cross the blood-brain barrier
C. causes vasoconstriction
D. is an opioid receptor agonist

**Core Concept:**
Sumatriptan is a medication primarily used for the treatment of migraine headaches. It belongs to a class of drugs known as triptans, which are selective serotonin receptor agonists. In this case, sumatriptan acts specifically on the 5-HT1B/1D receptors found on the smooth muscle cells of the meninges, which are the protective membranes covering the brain and spinal cord.

**Why the Correct Answer is Right:**
Sumatriptan is a highly specific serotonin receptor agonist targeting the 5-HT1B/1D receptors. This specificity allows it to constrict the blood vessels in the meninges, thereby reducing the intensity and duration of migraine headaches.

**Why Each Wrong Option is Incorrect:**
A. The statement "does not act specifically on the serotonin receptors" is incorrect because sumatriptan does indeed act specifically on the 5-HT1B/1D receptors, as mentioned above. This specificity is essential for its therapeutic effect on migraines.

B. Sumatriptan does cross the blood-brain barrier, which is the protective barrier that separates the blood from the central nervous system (CNS). Although it does not reach the CNS, it does exert its effects on the meningeal blood vessels, which are part of the peripheral nervous system (PNS).

C. The statement "causes vasoconstriction" is partially correct, as sumatriptan does constrict the blood vessels in the meninges. However, the correct term is "vasoconstriction," not "vasoconstriction," which is a less specific term.

D. Sumatriptan is not an opioid receptor agonist. Opioid receptors are a different class of receptors found in the CNS, while sumatriptan specifically acts on the 5-HT1B/1D receptors in the PNS.

**Clinical Pearls:**
Sumatriptan is a valuable medication for treating migraine headaches. Understanding the pharmacology of this medication allows for proper patient management and treatment decisions. Misunderstanding its pharmacology can lead to incorrect patient management and potential harm. Always ensure a deep understanding of a medication's mechanism of action before prescribing or administering it to a patient.