An OTC drug label indicates that adults with cold symptoms should take two teaspoons of the medicine every four hours. The frequency of this dosing schedule is determined by the drug’s

A drug’s half-life is the time it takes for the amount of the drug in the body to decrease by half. It helps determine how often a dose must be taken to maintain an effective level, so the four-hour schedule is determined by the drug’s half-life. A frequency distribution and median toxicity do not set dosing intervals, and off-label use means using a drug in a way not specified by its approved labeling.

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