Caffeine

Caffeine causes vasoconstriction that reduces cerebral blood flow by 27%. [1][3]
Caffeine is also able to reduce myocardial blood floow. [3]
Chronic moderate(405mg/day) use results an adaptation for the vasoconstriction. [1]
Caffeine significantly decrease reaction times in auditory and visual choice tasks. [2]
Moderate use of caffeine elevates mood and increases self-ratings of tension or anxiety for at least 3 hours. [2][3]
Moderate use of caffeine significantly increases latency to sleep and improves daytime alertness. [2][3]
Caffeine decreases vitamin D receptor protein expression.