Cytochrome P450 1A2 (CYP1A2) is involved in drug metabolism. This enzyme is responsible for the break down of 95% of the caffeine in the body.

Many genetic forms of the gene CYP1A2, which produces cytochrome P450 1A2, have been identified. Differences in caffeine sensitivity are due to the presence of two of these genetic forms – CYP1A^*1A and CYP1A^*1F.

People with the CYP1A2^*1A versionproduce more enzyme and are “fast” caffeine metabolizers. Whereas individuals with the CYP1A2^*1F version produce lower levels of enzyme and are “slow” metabolizers. Inheriting the *1F version makes you sensitive to caffeine.