The relationship between the doses of a drug required to produce undesired and desired effects.

A general way of measuring an effective dose of a drug and its toxicity.

Ratio between toxic and therapeutic doses (the higher the ratio, the greater the safety of the therapeutic dose)

The ratio of the dose required to produce toxic or lethal effect to dose required to produce nonadverse or therapeutic response.

an index based on the ratio of tumor control probability (TCP) to normal tissue complication probability (NTCP) used in radiation therapy to assess the likelihood of effective treatment vs. the likelihood damage to surrounding tissues

The therapeutic index (also known as therapeutic ratio or margin of safety), is a comparison of the amount of a therapeutic agent that causes the therapeutic effect to the amount that causes toxic effects. Quantitatively, it is the ratio given by the dose required to produce the toxic effect divided by the therapeutic dose. A commonly used measure of therapeutic index is the lethal dose of a drug for 50% of the population (LD50) divided by the effective dose for 50% of the population (ED50).