A little less jargon.

A health problem recorded during or after treatment, whether or not treatment caused it. An untoward medical occurrence during or after treatment or research, whether or not it was caused by the intervention. An adverse reaction is a separate causality judgement.

How strongly a molecule binds to a particular target under specified conditions. A measure of how strongly a molecule binds a particular target under specified conditions. Affinity is not the same as potency, efficacy, selectivity, or clinical benefit.

A substance that can activate a receptor’s response in a particular setting. A ligand that activates a receptor and produces a receptor-mediated response in a defined biological system. The response depends on the receptor, pathway, tissue, and assay.

A substance that can block or reduce another substance’s effect on a receptor. A ligand that reduces or prevents an agonist’s receptor-mediated effect without producing that same activation in the system being studied. Competitive, allosteric, and other forms exist.

How much of a medicine becomes available to act, and how quickly. The rate and extent to which an active ingredient becomes available at its site of action. For many systemic medicines, blood exposure is used to assess this; it does not directly measure concentration in every tissue.

A planned study in people that assigns or evaluates an intervention and prespecified outcomes according to a protocol. Not every study in people is a clinical trial.

What researchers compare a treatment against. The treatment, placebo or other strategy against which an intervention is assessed. The choice determines part of the question the study can answer.

What researchers measure, and when, to answer a study question. A defined measure and time point used to evaluate a study question. Primary, secondary, exploratory, clinical, and surrogate endpoints have different roles and limits.

A biological catalyst that helps a chemical reaction occur. Enzymes are one kind of medicine target.

How much of a substance reaches a part of the body over time. The amount or concentration of a substance to which the body, tissue, or target is exposed over time. It is different from the amount administered.

The time for a concentration to decrease by half in a specified model or part of a concentration curve. It is not necessarily the duration of an effect.

A chemical messenger made by cells that can act on cells with the machinery to respond. Many hormones travel through the bloodstream, while others act locally.

In plain English, a substance that fits into and binds a molecular target. A molecule that binds a molecular target, such as a receptor. Binding alone does not say whether it activates, blocks, or changes the target’s activity.

A molecular structure a substance is intended or observed to interact with, such as a receptor, enzyme, ion channel, or transporter. Target engagement is not proof of clinical benefit.

A chemical messenger released by a neuron that changes the activity of a receiving neuron, muscle cell, gland cell, or another target cell.

The characteristic or event measured to answer a research question. Its definition and time point belong with the result.

A substance that activates a receptor but produces a smaller maximum response than a full agonist in the same tested system. An agonist that produces a lower maximum response than a full agonist at saturating concentrations in a specified system. This does not mean half a dose.

A chain of amino acids joined by peptide bonds. The category does not establish a substance’s safety, effectiveness or regulatory status.

The study of a substance’s effects on the body, including concentration–effect relationships and intended or unintended responses. It is distinct from, but linked to, pharmacokinetics.

What the body does to a substance over time. The study of how the body handles a substance over time, including absorption, distribution, metabolism and excretion. It does not by itself show whether a treatment works.

A look-alike comparison treatment without the active component being tested. A comparison intervention designed to resemble the treatment while omitting its hypothesised active component. Expectations, care, and side effects can still affect outcomes.

How much of a substance is needed to produce a specified effect in a defined setting. The concentration or amount needed to produce a specified level of an effect in a defined system. Potency depends on the assay and does not by itself establish efficacy, safety, or treatment value.

A biological macromolecule made from one or more amino-acid chains whose sequence and three-dimensional structure help determine its functions. Many receptors and enzymes are proteins.

Assigning participants to study groups by chance. Allocating study participants by chance to help make the treatment comparison less vulnerable to systematic selection differences.

In plain English, a cell’s message receiver. Usually a protein in or on a cell that recognises and binds particular substances and can change cell signalling or activity. Binding, activation, and a clinical effect are different questions.

A linked set of molecular events by which a signal is detected, relayed, integrated, and terminated. Pathways can branch, interact, and act across cellular compartments.

A reduced response after repeated exposure, in the context being discussed. It should not be confused automatically with dependence or addiction.