When adenosine levels are low, caffeine ingestion is less likely to cause vasoconstriction and may lead to vasodilation.

“caffeine occupies The receptors for something called adenosine adenosine is a molecule that builds up in the brain and body more and more the longer we've been awake it's one of the things that makes us feel sleepy so when we drink caffeine that caffeine occupies the adenosine receptor and the adenosine cannot have its normal effect of making us sleepy when that caffeine wears off the adenosine combine and we feel sleepy adenosine is a vasodilator so when we drink caffeine because it blocks the effects of adenosine there is a vasoconstriction associated with drinking caffeine”

“caffeine is also a vasodilator caffeine has the ability to impinge on the so-called no pathway the nitric oxide pathway which is a nerve to blood pathway that causes dilation of the blood vessels”

“if however you haven't slept well or it's late in the day and you've been up for a long time drinking caffeine is likely to have more of a vasoconstriction effect”