Maximum response a drug can produce regardless of its dose is known as:

It is the maximum effect produced by a drug. The upper limit of DRC is the index of drug efficacy and refers to the maximal response that can be elicited by the drug, e.g. morphine produces a degree of analgesia not obtainable with any dose of aspirin-morphine is more efficacious than aspirin. Efficacy is a more decisive factor in the choice of a drug.