Are roadside drug field tests reliable?

Roadside field tests are screening tools. They aren't the same thing as a confirmatory laboratory analysis, and they can produce errors from contamination, from interpretation, or from cross-reactivity with substances that aren't controlled at all.

Two examples from actual cases make the point better than any general description. Tylenol has field tested positive for fentanyl. And actual controlled substances have field tested negative, only to come back positive from the lab later.

Errors run in both directions, which is the part people miss. A positive field test is not proof, and a negative one is not clearance.

That's why a serious drug case has to be evaluated using the actual lab result and the chain of custody, rather than the roadside result that produced the arrest. The field test justified a decision at the scene. It isn't the evidence the case gets tried on.

If a field test has come back positive or negative in your case, that's the moment to involve counsel.