One enzyme does most of the clearing
Roughly 95 percent of caffeine is broken down in the liver by the enzyme CYP1A2, and a common variant in the CYP1A2 gene influences how fast that enzyme works. People carrying the AA genotype are generally classified as fast metabolizers who clear caffeine quickly, while those with AC or CC genotypes tend to be slower metabolizers in whom caffeine lingers longer.
This genetic difference helps explain why the same espresso leaves one person calm and another jittery hours later.
Slow metabolizers and cardiovascular risk
Some observational research suggests slow metabolizers who drink larger amounts of coffee may carry a higher cardiovascular risk than fast metabolizers at the same intake, while moderate intake appears broadly safe for most people. These associations come from population studies and do not prove that a given individual will be harmed, and a single gene does not capture the full picture of caffeine response.
This is general educational information, not medical advice. Genotype-based decisions about caffeine, especially with existing heart concerns, should be made with a qualified professional rather than from a chart alone.