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Efficacy is the desired effect (e.g. analgesia). Some drugs (e.g. morphine) have greater analgesic effect than others (e.g. paracetamol).

Each drug has its own Emax and EC50. The Emax of paracetamol is lower than the Emax of morphine.

Move the slider to see what happens when efficacy changes but potency remains constant.

Effect (%)

Concentration (log)

Low High