[_yb2s]

CYP1A2 is the whole gene- you need to look at marker rs762551 within CYP1A2. Both the C/C and A/C genotype are slow caffeine metabolizers. The most common genotype is A/A, which is a fast metabolizer.

https://www.ncbi.nlm.nih.gov/snp/rs762551

[jamroom]

Do you have a link to one that shows A/C? I'm only seeing C/C (I'm A/C so curious). Thanks!

[_yb2s]

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2014233/

This seems to be the original paper. I don't find this paper particularly meaningful, but the effects they did observe showed A/C and C/C to be about the same, and both different than A/A.

This is based on a 5 hour after caffeine ingestion blood test in smokers. They found no differences in the non-smokers, but those were urine tests taken at variable times (whenever they peed), which seems sketchy to me.

Based on this study, subsequent studies (e.g. https://pubmed.ncbi.nlm.nih.gov/16522833/) seem to group A/C and C/C together, and not look at them independently. C/C is rare enough that studies have trouble getting many individuals from that group.