Peptide glossary

Terms

Agonist

A substance that switches on a receptor in the body. GLP-1 medicines are GLP-1 receptor agonists: they act like the natural hormone.

Amylin

A hormone released with insulin that is involved in fullness. Pramlintide and cagrilintide are man-made versions.

Bacteriostatic water

Sterile water with a preservative that slows the growth of bacteria. It is often used to mix freeze-dried powders. Use what your product instructions call for.

Compounded medicine

A medicine a pharmacy makes for a patient, instead of an approved product. The FDA says compounded drugs do not go through its approval process, so it does not check their safety, effectiveness or quality before they reach the market.

Concentration

How much of a substance is in each mL of liquid, for example 5 mg/mL. It changes if you add a different amount of water to a vial, so write it down.

Dose escalation

Raising a dose in steps over time. Also called titration. The steps come from the label and your prescriber.

Elimination half-life

The time it takes for the amount of a medicine in the body to fall by half. The U.S. labels give about 1 week for semaglutide, and about 5 days for tirzepatide.

Eructation

The medical word for burping. It is the term used on GLP-1 labels.

GIP

Glucose-dependent insulinotropic polypeptide, a gut hormone. Tirzepatide acts on GIP and GLP-1 receptors.

GLP-1

Glucagon-like peptide-1, a gut hormone involved in blood sugar and appetite. Semaglutide and liraglutide act on its receptor.

Glucagon

A hormone that raises blood sugar. Retatrutide and survodutide are studied for acting on its receptor as well as GLP-1.

HbA1c

A blood test showing average blood sugar over about the past three months. Diabetes trials often report it.

Intramuscular

Into a muscle. Many hormone injections in oil are given this way.

Investigational

Being studied in clinical trials and not yet approved for general use.

Label

The official prescribing information for an approved medicine. In the U.S. you can read labels on DailyMed. It is the first place to check a fact about a medicine.

Lean mass

Everything in the body except fat, which includes muscle, water and organs. It is not the same as muscle.

Lyophilised

Freeze-dried into a powder, to be mixed with liquid before use. Many peptides are sold this way.

Maintenance dose

The dose a person stays on after any dose increases. It comes from the label and your prescriber.

mcg and mg

Both are units of weight. 1 mg is 1,000 mcg, so mixing them up is a 1,000-fold error. Write the unit next to every number.

Microdosing

An informal word for taking less than a labeled dose. It is not a term on the labels, and it is not a dose schedule from a regulator. Ask your prescriber.

Off-label

Using an approved medicine for a purpose, or in a way, that its label does not list.

Peptide

A short chain of amino acids, the building blocks of proteins. Some peptides are approved medicines, such as semaglutide, and many are not.

Placebo

A dummy treatment with no active medicine, used in trials to show what happens without the medicine.

Priming

Pushing a small amount of medicine through a pen before injecting, to clear air and check that it works. Follow your pen's instructions.

Reconstitution

Mixing a freeze-dried powder with a liquid to make a solution. See the reconstitution calculator.

Research use only

A label on products sold for laboratory work. It does not mean a product is approved or checked for use in people.

Secretagogue

A substance that prompts the body to release something. Growth hormone secretagogues prompt the release of growth hormone.

Steady state

When the amount of a medicine in the body settles into a regular pattern with repeat doses. The labels give about 4 to 5 weeks for weekly semaglutide on Ozempic, and 4 weeks for tirzepatide.

Subcutaneous

Under the skin. GLP-1 pens are injected this way, usually in the abdomen or thigh, or the upper arm for some products.

Titration

Changing a dose in steps until reaching the intended dose. See the titration planner.

U-100 syringe

A syringe marked so that 100 units equal 1 mL. Units measure volume on the syringe, not the amount of medicine. See the units calculator.

Vial

A small sealed bottle of medicine. Unlike a pen, the dose you draw depends on the strength on its label and your syringe. See the vial tracker.

Compounds

See the status of more than 50 compounds, from approved medicines to research chemicals.

Useful pages

Reko records what you and your prescriber decide. It never suggests a dose, and this page is not medical advice.