coffee and other caffeine containing products such as tea, soda, and even chocolates are vasoconstrictors.meaning they constrict your veins that s why you get high blood pressure.they re actually stimulants that s why people are refrained from consuming those things at night. for how long, well it depends to the person whose drinking.some people are not really affected because they are some what immuned to the effect of cxaffeine while others are not. but drinking 1 cup of coffee doesn t necessarily mean that you would immediately get a hugh blood pressure at once.