Peptide glossary

Agonist

A substance that switches a receptor on, mimicking a natural hormone or signal. Semaglutide is a GLP-1 receptor agonist.

Amino acid

The building blocks of peptides and proteins. Peptides are short chains of amino acids; proteins are long ones.

Analogue

Also: Analog

A modified version of a natural molecule, changed to last longer or work more strongly. Tesamorelin is an analogue of growth-hormone-releasing hormone.

Bacteriostatic water

Also: BAC water

Sterile water with a small amount of benzyl alcohol that stops bacteria growing, so a mixed vial can be used more than once. Not the same as plain sterile water.

Beyond-use date

The date after which a mixed (reconstituted) vial shouldn't be used, because the peptide may break down or the vial may become contaminated.

Blend

A vial that contains more than one peptide, such as GLOW. Every dose drawn from it contains all of them, in the same ratio.

Compounding

When a pharmacy makes a version of a medicine itself instead of using a manufacturer's product. Rules on which substances can be compounded vary by country and change over time.

Concentration

How much peptide is in each mL of liquid after mixing, in mg/mL. It equals the amount in the vial divided by the water added.

Contraindication

A reason not to use a medicine, such as a medical condition or another medicine that makes it unsafe.

GLP-1

Also: Glucagon-like peptide-1

Glucagon-like peptide-1, a gut hormone released after eating. It increases insulin when blood sugar is high, slows the stomach and reduces appetite. Drugs like semaglutide copy it.

Growth hormone secretagogue

Also: GHS

Anything that makes the pituitary gland release growth hormone, such as ipamorelin, GHRP-2 or MK-677.

Half-life

How long it takes for the amount in the body to fall by half. A longer half-life usually means less frequent doses.

IGF-1

Also: Insulin-like growth factor 1

Insulin-like growth factor 1, made mainly by the liver in response to growth hormone. It drives many of growth hormone's effects on muscle and bone.

Intramuscular (IM)

Also: IM

An injection into a muscle, such as the thigh or shoulder.

Lyophilised

Also: Lyophilized, Freeze-dried

Freeze-dried. Many peptides come as a dry powder or 'cake' in the vial, which keeps them stable until water is added.

mcg and mg

Also: Microgram, Milligram, µg

Units of weight. 1 mg (milligram) = 1,000 mcg (micrograms). Peptide doses are often in mcg; vial sizes are usually in mg.

Off-label

Using an approved medicine for a condition, dose or group of people it isn't officially licensed for. Doctors can prescribe off-label, but the evidence is often weaker.

Peptide

A short chain of amino acids, usually 2 to 50. Many hormones, such as insulin and oxytocin, are peptides.

Phase 1, 2 and 3 trials

Also: Clinical trial phases

The stages of testing a new medicine in people. Phase 1 checks safety in small groups, phase 2 tests whether it works and at what dose, and phase 3 compares it with existing treatment or placebo in large groups.

Placebo

A dummy treatment with no active ingredient, used in trials to show whether a medicine works better than expectation alone.

Randomised controlled trial (RCT)

Also: RCT, Randomized controlled trial

A study where people are randomly given the treatment or a comparison (often placebo). It is the strongest single type of evidence for whether a treatment works.

Receptor

A protein on or in a cell that a hormone or drug binds to, triggering an effect. Each peptide works through specific receptors.

Reconstitution

Mixing a freeze-dried powder with a liquid, usually bacteriostatic water, so it can be injected.

Research chemical

A label sellers use for compounds that aren't approved as medicines. They aren't made or checked to medicine standards, so purity and contents can vary.

Subcutaneous (SC)

Also: SC, SubQ

An injection into the fatty layer just under the skin, such as the belly or thigh. Most peptides are given this way.

U-100 insulin syringe

Also: Insulin syringe, Units

A syringe marked in units, where 100 units = 1 mL. So 1 unit is 0.01 mL, whatever the syringe's total size (30, 50 or 100 units).

WADA

Also: World Anti-Doping Agency

The World Anti-Doping Agency, which publishes the list of substances banned in sport. Many peptides, including BPC-157 and growth hormone releasers, are on it.