Comment by dane-pgp

It's worth noting that drug laws don't necessarily treat substances as being in your possession once they have been consumed, and although they might criminalize the "use" of drugs, that can require proving intent, which is not necessarily possible to establish solely from the presence of the substances (or their metabolites) in the suspect's blood.

The 1993 case State v. Lowe gives a good explanation of the legal reasoning:

"The absence of proof to evince knowledgeable possession is the key. The drug might have been injected involuntarily, or introduced by artifice, into the defendant's system."

https://www.leagle.com/decision/199383586ohioapp3d7491724