Potency vs. Strength — What's the Difference?

Potency measures how much of a drug is required to produce a desired effect. A highly potent drug achieves its therapeutic effect at a low dose, meaning less of the drug is needed to elicit the same response. For example, a potent painkiller like fentanyl requires only a small dose to relieve pain compared to less potent drugs. On the other hand, strength refers to the concentration of the active ingredient in a drug formulation. It is typically expressed in milligrams (mg) or other units per dose. For instance, a medication might have a strength of 500 mg per tablet, indicating the amount of active substance present.

In pharmacology, potency is crucial when determining the dosage needed for treatment. A drug with higher potency will require a lower dose to achieve the same effect as a drug with lower potency. Strength, however, helps in formulating the drug and ensures consistent delivery of the active ingredient in each dose. Both are essential for effective treatment, but they address different aspects of drug efficacy and formulation.

Potency also plays a role in drug comparison. Two drugs can have the same therapeutic effect, but the one with higher potency will do so at a lower dose. Conversely, strength is used to specify the amount of drug in a particular dosage form, which is important for accurate prescribing and dispensing.

In terms of side effects, a drug with higher potency might have a higher risk of side effects at therapeutic doses if not carefully monitored. Strength impacts how a drug is administered and how often it needs to be taken, which affects patient compliance and convenience.