Stay away from 23andme if you have any privacy concerns. I've worked with providers of DNA insights and advice that don't build their revenue model on selling your data. For example DNAPal.me
They do not sell your data; Facebook and Google also don't sell your data.
Your DNA is worthless[0] and impossible to hide. If someone did want your DNA there is nothing you could do to stop them. You leave it everywhere you go.
[0] except to your children you don't know you have
Yeah, but why not support companies doing "the right thing" and nudge the trend towards companies that respect and preserve the privacy interests of their customers.
I really wish there were more outlets like how for the legal/news junkie circuit we have things like MeidasTouch or whatever its called and the other YouTuber journalists (they deserve that umofficial title because what they do is top shelf journalism or at least investigative YouTubing.
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.
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.
Then look at CYP1A2, see if you have the C/C genotype.
Definitely read the Genetic Life Hacks article that I linked to above.