Is there a drug/substance, that...

[0utrider]

Is there a drug or substance that can be administered, preferably orally, that is or would reasonably considered a "drug" (in the intoxicating sense) that nevertheless won't actually pass the BBB into the Brain, yet is relatively unkown OR is also possible to be consumed in a way that it does cross the BBB but also in a way that it doesn't?
legally speaking, a blood test on let's say drug XYZ, which can be consumed nasally and ends up in the brain (and blood) can also be consumed orally and only ends up in the bloodstream but not in the brain, thus leading to conclusions for the law enforcement that one is intoxicated while he actually isn't. Is there such thing?
SWIM was thinking about either drugs that can only effectively be consumed nasally and otherwise won't cross the BBB but are still in the bloodstream? What would that be? DMT? Or a drug that mimmicks a different drug that it is closely related to and/or has the same metabolites but actually is not potent itself. let's say melatonin which is awfully close to certain tryptamines, or maybe phenetylalanine, which is active but comparatively weak.. could it be confused for an "actual" (in the stigmatizing sense) drug by merely testing the blood?