A researcher analyzes the interaction between two investigational drugs. He begins by plotting the dose–response curve for the first drug, administered alone. He then administers both drugs in combination and plots a second dose–response curve. When the two drugs are co-administered, the dose–response curve is shifted significantly to the right. He concludes, therefore, that the interaction between the two drugs is:__________

A researcher analyzes the interaction between two investigational drugs. He begins by plotting the dose–response curve for the first drug, administered alone. He then administers both drugs in combination and plots a second dose–response curve. When the two drugs are co-administered, the dose–response curve is shifted significantly to the right. He concludes, therefore, that the interaction between the two drugs is antagonistic.

An antagonist is sometimes called blockers and it is simply referred to as a type of drug that avoids a biological reaction. An antagonist doesn't activate when it binds to the receptor but what it does is that it blocks the receptor. From the question, we are told that when the two drugs are co-administered, the dose–response curve is shifted significantly to the right, this implies that the interaction is antagonistic.