Glossary
Terms, in plain language
21 terms used across the library, explained without assuming a biochemistry degree.
- Agonist
- A molecule that binds a receptor and switches it on. Semaglutide is a GLP-1 receptor agonist: it activates the same receptor as the body's own GLP-1.
- Amino acid
- The building block of peptides and proteins. Twenty standard amino acids are linked together in a specific order, and that order determines what the peptide does.
- Anecdotal evidence
- Reports of personal experience without a controlled comparison. It cannot separate a real effect from expectation, natural recovery or coincidence.
- Antagonist
- A molecule that binds a receptor and blocks it, preventing activation rather than causing it.
- Bioavailability
- The fraction of a dose that actually reaches the bloodstream in active form. Most peptides have very low oral bioavailability because digestive enzymes break them down.
- GIP
- Glucose-dependent insulinotropic polypeptide, the other main incretin hormone. Tirzepatide activates both GIP and GLP-1 receptors.
- GLP-1
- Glucagon-like peptide-1, a hormone released from the gut after meals. It boosts insulin release, slows stomach emptying and reduces appetite.
- Half-life
- The time it takes for half of a substance to be cleared from the blood. A short half-life means frequent dosing; a long one allows weekly dosing.
- IGF-1
- Insulin-like growth factor 1, a hormone made mainly in the liver in response to growth hormone. It is often measured as a downstream marker of growth hormone activity.
- Incretin
- A gut hormone released after eating that increases insulin release. GLP-1 and GIP are the two main incretins, and both are targets of modern diabetes drugs.
- Off-label use
- Using an approved medicine for a condition, dose or route it was not approved for. It can be legal and sometimes evidence-based, but it is not the same as proven use.
- Peptide
- A short chain of amino acids, usually fewer than 50. Proteins are longer chains; the boundary is rough. Many hormones and signalling molecules in the body are peptides.
- Peptide bond
- The chemical link between two amino acids. It forms when one amino acid's acid group joins the next one's nitrogen group, releasing water.
- Pharmacokinetics
- What the body does to a substance: how fast it is absorbed, where it goes, how it is broken down and how it leaves. Usually summarised as absorption, distribution, metabolism and excretion.
- Placebo-controlled trial
- A study in which one group receives the treatment and another receives an inactive dummy, with neither knowing which is which. It is the standard way to show a real effect.
- Randomised trial
- A study in which participants are assigned to treatment or control by chance. Randomisation prevents bias in who gets which treatment.
- Receptor
- A protein on or inside a cell that recognises a specific molecule and passes its signal inward. A peptide usually works by binding to one or more receptors.
- Research chemical
- A substance sold for laboratory research rather than human use. It is not quality-controlled for human use, and purity is the buyer's risk.
- Secretagogue
- A substance that stimulates another cell to secrete something. A growth hormone secretagogue triggers the pituitary to release growth hormone.
- Somatostatin
- A hormone that inhibits growth hormone release. Drugs called somatostatin analogues act as a brake on the same system that secretagogues push.
- Subcutaneous injection
- An injection into the fat layer just under the skin. It is the most common route for peptide medicines because it gives slow, predictable absorption.