Hi, would I be correct in saying that while someone is under the influence of a recreational type drug this would alter the persons Blood Pressure?

The reason I ask this is I recently failed a drug-test, however I hadn't taken any drugs for at least 6 months prior to the test yet it registered quite a large amount. I believe its a false reading, but i need proof.

During the drug-test I had my blood pressure taken and my heart rate checked and these both checked perfect, and i am generally a very fit person.

If i was under the influence of drugs (amphetamines according to the result) then this would mean my blood pressure and heart rate would be altered quite significantly. But they were normal, which would lead me to believe its impossible that i was under any influence of drugs.

Is this correct???