What term describes a drug's effectiveness?

The term that describes a drug's effectiveness is efficacy. Efficacy refers to the ability of a drug to produce the intended therapeutic effect under ideal circumstances. It indicates how well a drug works when given to patients in clinical trials. Efficacy is measured by various parameters, including how much of the drug is needed to produce the desired response, usually in controlled settings.

Potency, while related to the effectiveness of a drug, specifically refers to the amount of the drug needed to achieve a particular effect. A more potent drug requires a lower dose to produce the same effect as a less potent drug.

Bioavailability is concerned with the proportion of the drug that enters the systemic circulation when introduced into the body and is available for action. It does not directly measure the drug's effectiveness.

Toxicity refers to the degree to which a substance can harm humans or animals and is not a measure of effectiveness.

Thus, efficacy focuses on the drug's ability to achieve the desired therapeutic outcomes, making it the correct term to describe a drug's effectiveness.