A drug that shifts dose response curve to left has:

Ans. B. More potencyPosition of curve indicates potency and height of curve indicates efficacy. Left ward shift indicates increase in potency of the drug.Potency: amount of drug necessary to produce a given response.a. EC50 - The concentration of drug producing an effect that is 50 percent of the maximum is used to determine potency and is commonly designated as the EC50 . The smaller the EC50 , more is the potency of a drugb. Potency is given by position on DRC. The more leftward the curve, the more potent is drugEfficacy: maximum response produced by any dose of a druga. It is analogous to the maximal velocity (Vmax ) for a reactionb. In clinical setting, efficacy is more important than drug potencyc. Efficacy is given by height of DRC. Higher the curve, more efficacious is the drug