Absorption: The first stage of pharmacokinetics; medications enter the body and travel from site of administration into the body’s circulation.

Adverse effect: An unintended and potentially dangerous pharmacological effect that occurs when a medication is administered correctly.

Affinity: The strength of binding between drug and receptor.

Agonist: A drug that binds to a “receptor” and produces an effect.

Antagonist: A molecule that prevents the action of other molecules, often by competing for a cellular receptor; opposite of agonist.

Bioavailability: The presence of a drug in the bloodstream after it is administered.

Blood-brain barrier: A nearly impenetrable barricade that is built from a tightly woven mesh of capillaries cemented together to protect the brain from potentially dangerous substances such as poisons or viruses.

Distribution: The second stage of pharmacokinetics; the process by which medication is distributed throughout the body.

Dose-response: As the dose of a drug increases, the response should also increase. The slope of the curve is characteristic of the particular drug-receptor interaction.

Duration: The length of time that a medication is producing its desired therapeutic effect.

Efficacy: The maximum effect of which the drug is capable.

Excretion: The final stage of pharmacokinetics; the process whereby drug byproducts and metabolites are eliminated from the body.

First-pass effect: The inactivation of orally or enterally administered drugs in the liver and intestines.

Mechanism of action: How a medication works at a cellular level within the body.

Metabolism: The breakdown of a drug molecule via enzymes in the liver (primarily) or intestines (secondarily).

Onset: When a medication first begins to work and exerts a therapeutic effect.

Peak: When the maximum concentration of a drug is in the bloodstream.

Pharmacodynamics: The study of how drugs act at target sites of action in the body.

Pharmacogenetics: The study of how a person’s genetic makeup affects their response to medicines.

Pharmacokinetics: The study of how the body absorbs, distributes, metabolizes, and eliminates drugs.

Pharmacology: The science dealing with actions of drugs on the body.

Pharmacy: The science of the preparation of drugs.

Potency: The drug dose required to produce a specific intensity of effect.

Selectivity: A “selective” drug binds to a primary and predictable site creating one desired effect. A “nonselective” drug can bind to many different and unpredictable receptor sites with potential side effects.

Side effect: Effect of a drug, other than the desired effect, sometimes in an organ other than the target organ.

Therapeutic index: A quantitative measurement of the relative safety of a drug that compares the amount of drug that produces a therapeutic effect versus the amount of drug that produces a toxic effect. Medication with a large therapeutic index is safer than a medication with a small therapeutic index.

Therapeutic window: The dosing window in which the safest and most effective treatment will occur.