Your body's membranes absorb caffeine very quickly, so you should feel the effects of caffeine within 15 to 45 minutes of consuming caffeine, but depending on the physiology of a person, it has been known for caffeine to affect some people within just 5 minutes.
How does the body process caffeine?
After the body’s membranes have done the work of absorbing the caffeine, a group of enzymes in the liver metabolize and degrade the caffeine.
Your genetic makeup determines how much of the enzyme you produce, so this means that while some individuals metabolize (or break down) caffeine extremely slowly, others do so quickly that they hardly notice its stimulating effects. It really depends on the individual!
You can only truly understand how you process caffeine by actually drinking it and watching what happens. The "coffee jitters," which can include heart palpitations, nausea, diarrhoea, restlessness, anxiety, and irritability, could be experienced by people who are hypersensitive to caffeine, even in small doses (like half a cup of coffee).
Whereas, if you are hyposensitive, this means that caffeine does not have a strong effect on you a normal dose won't have much of a stimulating effect, even if you've never had coffee before.