<prompt> Drug H is most likeEpinephrineIsoproterenolNorepinephrinePhenylephrine  <response>: The effects of Drug H are changed by treatment with either an alpha or beta blocker, so Drug H must have activity at both receptors choices B, D, and E are ruled out. Reversal of a pressor effect can only occur if the drug has beta2 activity choice C is ruled out. Drug H is epinephrine. 