ED 50 is a measure of:
Potency can be defined as the concentration of drug EC50 or dose ED50 of a drug required to produce fifty percent of that drug's maximum Therapeutic effect. Ref: KDT, 6th Edition, Pages 53, 54; Basic and Clinical Pharmacology By Beram Katzung, 10th Edition, Page 28; Pahrmacology By Gary. C. Rosenfeld, David S. Loose, 4th Edition, Page 5
Toxicity
Safety
Potency
Efficacy