Caffeine is a central nervous system stimulant.
Caffeine is a stimulant, and a stimulant constricts blood vessels.
Caffeine constricts blood vessels.
What does caffeine do to blood vessels?

[1] It expands
[2] looseness
[3] hydrate their cells
[4] Constrict them
[5] sweating
[6] Dehydration
[7] They may not survive.
[8] Damages them