Glossary

One of the small molecules that link together in a chain to form peptides and proteins.

Twenty amino acids make up almost everything in human biology. The order they appear in determines what the finished peptide or protein does.

An enzyme that acts as the cell's fuel gauge — when energy runs low, it switches the cell from storing energy to producing it.

AMPK is activated by things that deplete cellular energy, including exercise and fasting. Because so many interventions converge on it, 'activates AMPK' on its own says very little about whether something is useful — it describes a mechanism, not an outcome.

Sterile water containing a preservative that inhibits bacterial growth, used as a diluent in research settings.

It is distinguished from plain sterile water by the preservative, which is what allows a reconstituted vial to be used more than once. Which diluent a given protocol specifies is a detail worth checking rather than assuming.

How much of a substance actually reaches the bloodstream in a form the body can use.

Bioavailability is a recurring problem for peptides specifically: they are chains of amino acids, and the digestive system is very good at breaking chains of amino acids apart.

How much of a substance is present in a given volume of liquid — for example, milligrams per millilitre.

Concentration is what turns an amount into a volume you can actually measure. Two vials containing different amounts can produce identical concentrations, and identical vials can produce different ones, depending entirely on how much liquid was added.

A label describing how much confidence a body of research actually supports.

Pep My Life grades every compound and claim on a five-step scale, from mechanistic reasoning through to established human trials. The scale is explained in full on the research methodology page.

Latin for 'in glass' — research done on cells or tissue in a dish rather than in a living body.

In vitro results are the furthest removed from real-world outcomes. A compound can behave one way in isolated cells and behave completely differently once digestion, circulation and the immune system are involved.

Research carried out in a living organism — an animal or a person.

Structures inside almost every cell that convert food and oxygen into usable energy.

Mitochondria are unusual because they carry their own small set of DNA, separate from the DNA in the cell nucleus. That quirk is what makes mitochondrial-derived peptides possible.

A peptide whose instructions are written in mitochondrial DNA rather than in the cell's main genome.

This category is small and relatively recently described. It matters because it suggests mitochondria do not only produce energy — they may also send chemical messages to the rest of the body.

A study that watches what happens naturally instead of changing something and measuring the result.

Observational studies can show that two things occur together. They cannot on their own show that one caused the other — that requires an intervention with a comparison group.

A short chain of amino acids — the same building blocks proteins are made from, just far fewer of them.

The line between a peptide and a protein is a matter of convention rather than chemistry: chains of roughly fifty amino acids or fewer are usually called peptides. Because they are short, many peptides act as signals — they tell cells to do something rather than doing structural work themselves.

Research done before human testing begins — usually in cells or in animals.

Preclinical work is how almost every idea starts, and most ideas stop there. A promising preclinical result is a reason to keep investigating, not evidence that something works in people.

A study where participants are randomly assigned to receive either the thing being tested or a comparison, so the two groups can be fairly compared.

Randomisation is what makes it possible to attribute a difference to the intervention rather than to who happened to be in each group. It is the strongest routine tool for establishing cause.

Adding liquid to a freeze-dried vial so its contents become a measurable solution.

The volume of liquid added determines the concentration of the result. The same vial reconstituted with different volumes produces different concentrations, which is why practical guidance has to be specific about both the vial strength and the volume.

The total amount of compound contained in a single vial before any liquid is added.

Vial strength is the starting point for every calculation that follows it. Guidance written for one strength does not transfer to another, which is why practical guides on this site are published per strength rather than per compound.