How do they do genetic testing for drugs when they swab your mouth?

Possible:metabolites: of some drugs. More commonly promoted for genetic patterns associated with known drug clearance pathways; rates of metabolism/ clearance of certain drugs. Theory: such knowledge could help predict/guide effective/safer dosages. However, still expensive & testing for many agents you will never use=of unclear value vs. careful use/trials of agents likely to be helpful for your actual issue(s).

DNA analysis: There are saliva tests for drugs where one can actually detect the drug or metabolites of the drug in saliva. This type of testing is NOT genetic testing. In genetic testing, we are usually doing DNA testing to see how one metabolizes drugs. This is based on a DNA profile. Since your DNA is found in all of your cells, we can get cells from really anywhere but saliva tends to be easy