Opioids can cause hypotension primarily through which mechanism?

• A. Increased heart rate
• B. Peripheral vasodilation
• C. Vasoconstriction
• D. Fluid retention

Answer: (B)

Opioids lower blood pressure mainly because they cause peripheral vasodilation, which reduces systemic vascular resistance. This effect is often due to histamine release from mast cells in response to some opioids (like morphine), leading to dilation of both arteries and veins. When vessels widen, blood pools in the periphery and venous return to the heart drops, along with a drop in afterload, so the mean arterial pressure falls. Some opioids may also dampen sympathetic tone, contributing to the drop, but the dominant mechanism is vasodilation. The other options imply mechanisms that would either raise blood pressure (vasoconstriction, increased heart rate) or increase fluid volume (fluid retention), so they don’t explain the hypotension as effectively.