10:18 Apr 27, 2011 

Strength, potency, and effectiveness
· Strength is the amount of drug in a given dosage form, for example, 500 mg/tablet.
· Potency refers to the relative strengths of medications that can produce the same effect. The drug with the
lowest strength to produce the effect is said to be the most potent. Strength is often used interchangeably with
potency, but they are not the same thing. Potency starts with the effect and examines the relative strengths of
different drugs able to produce that effect, while the word “strength” itself does not imply anything about effect.
· Effectiveness refers to the percent of patients who will have a desired response to a drug. Strength can be
confused with effectiveness when a patient asks if one drug is stronger than another. What the patient really
wants to know is whether one drug is more likely to produce a desired effect compared to the other.