Potency refers to the relative strength of a medication. It’s not to be confused with “efficacy,” or how well the medication works. The question of potency most frequently gets raised when people are either starting a new medication or are switching between medications in the same class.
For instance, if someone is on the high potency antipsychotic medication risperidone (Risperdal), he’s likely taking a few milligrams a day, on the order of 1–6. If he’s being switched to a low-potency antipsychotic such as quetiapine (Seroquel) he could expect to be on a few hundred milligrams.
Both drugs are equally efficacious, but their relative potencies are different. In other words, even though the doses look quite different they do the same thing.