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Glossary

The vocabulary you meet in the entries, explained briefly. Where a term is contested or used loosely outside clinical medicine, the entry says so.

52 terms

Basics

Agonist: A molecule that binds a receptor and activates it, producing the same kind of response as the body's own signalling molecule. An antagonist binds the same receptor but blocks it instead.
Amino acid: The building block of peptides and proteins. Twenty standard amino acids are encoded genetically; the order in which they are linked determines a peptide's shape and what it binds to.
Infradian rhythm: A biological cycle longer than 24 hours — the menstrual cycle is the standard example — as opposed to a circadian rhythm, which is roughly daily. The term is descriptive and carries no therapeutic implication on its own.
Lyophilized: Freeze-dried. Water is removed from a frozen solution under vacuum, leaving a dry powder that is more stable in storage than a liquid. A lyophilized peptide must be reconstituted with a suitable diluent before it can be used.
Mitochondria: Organelles that generate most of a cell's ATP through oxidative phosphorylation. They carry their own small genome, and their function is a recurring theme in metabolic and longevity research.
NSAIDs: Non-steroidal anti-inflammatory drugs, such as ibuprofen and naproxen, which reduce inflammation and pain by inhibiting cyclooxygenase enzymes. They appear in peptide literature mainly as comparators in tissue-healing studies.
Peptide: A short chain of amino acids joined by peptide bonds, conventionally up to about 50 residues; longer chains are called proteins. Many peptides act as signalling molecules, binding a receptor to trigger a specific cellular response.

Administration

Bacteriostatic water: Sterile water containing a preservative, usually 0.9% benzyl alcohol, which inhibits bacterial growth and allows a vial to be entered more than once. It is distinct from plain sterile water, which has no preservative.
Intramuscular (IM): Into a muscle. The richer blood supply generally gives faster absorption than a subcutaneous injection. Some approved products, such as chorionic gonadotropin, specify this route exclusively.
ISR (injection-site reaction): A local reaction where an injection was given — redness, swelling, itching, induration or pain. Injection-site reactions are recorded as adverse events in clinical trials and appear on approved labels.
Local: Acting at or near the site of application rather than throughout the body. Whether a given compound genuinely stays local is an empirical question, not something the route guarantees.
PIP (post-injection pain): Pain at an injection site in the hours or days after an injection. It is a colloquial term from user communities rather than a clinical classification.
Reconstitution: Dissolving a lyophilized powder in a liquid to produce a solution. The choice and volume of diluent determine the final concentration, so the same vial can yield very different amounts per unit volume.
Subcutaneous (SubQ): Into the fatty layer just beneath the skin. Absorption is slower and steadier than from a muscle, which is why most approved peptide medicines are given this way.
Systemic: Acting throughout the body after reaching the general circulation, as opposed to acting only where it was applied.
Titration: Adjusting a dose in steps toward a target, typically starting low to improve tolerability. Approved GLP-1 medicines are titrated over weeks, and their labels state that the starting dose is not a maintenance dose.

Technical & analysis

Bioavailability: The fraction of an administered dose that reaches the systemic circulation unchanged. Peptides taken by mouth generally have very low bioavailability because digestive enzymes break them down, which is why most are injected.
COA (certificate of analysis): A document reporting laboratory testing of a specific batch, typically identity and purity. A certificate is only as good as the laboratory that issued it and the chain of custody linking it to the vial in hand.
Downregulation: A decrease in receptor number or in gene or protein expression, reducing sensitivity or output. Sustained receptor stimulation can itself drive downregulation.
Exosomes: Small membrane-bound vesicles released by cells, carrying proteins and nucleic acids between them. They are an active research area in cell signalling; marketed exosome products are largely unapproved.
Half-life: The time taken for the concentration of a substance in plasma to fall by half. It governs dosing frequency, and it is route- and formulation-dependent — the same molecule can show very different half-lives as a free peptide and as a controlled-release implant.
HPLC: High-performance liquid chromatography, a technique that separates the components of a mixture so their relative amounts can be measured. It is the usual basis for a stated purity percentage.
Mass spectrometry: A technique that measures mass-to-charge ratio to identify what a sample contains. Where chromatography shows how much of something is present, mass spectrometry addresses whether it is the intended molecule at all.
Upregulation: An increase in the number of receptors on a cell, or in the expression of a gene or protein, raising sensitivity or output.

Healing

Actin: A structural protein that forms filaments in the cytoskeleton, driving cell shape, movement and division. F-actin is the filamentous form; cell migration in healing assays depends on it.
Angiogenesis: The formation of new blood vessels from existing ones. It supports tissue repair by improving blood supply, and it is the mechanism most often proposed for peptides studied in healing models — the same mechanism that raises theoretical caution about tumour blood supply.
Fibroblast: The connective-tissue cell that produces collagen and other extracellular matrix components. Fibroblast migration and survival are common endpoints in tendon and wound-healing studies.
Proliferation: Cell division and growth in number. In wound healing it names the phase in which new tissue and vasculature are laid down, following the inflammatory phase.
Remodeling: The final and longest phase of wound healing, in which newly deposited collagen is reorganised and cross-linked, gradually increasing tensile strength. Repaired tissue rarely regains the properties of the original.

Metabolic

ATP: Adenosine triphosphate, the molecule cells use to carry chemical energy. Most is produced in mitochondria, and its turnover is rapid rather than stored in quantity.
Autophagy: A cellular recycling process in which damaged components are enclosed and delivered to lysosomes for breakdown. It is heavily studied in ageing and metabolic research, though translating it into human outcomes remains difficult.
Gastroparesis: Delayed emptying of the stomach without a mechanical obstruction, causing nausea, early fullness and vomiting. Because GLP-1 receptor agonists slow gastric emptying by design, this is a recognised safety consideration for that class.
GIP: Glucose-dependent insulinotropic polypeptide, the other major incretin hormone alongside GLP-1. Tirzepatide acts at both the GIP and GLP-1 receptors.
GLP-1: Glucagon-like peptide-1, a hormone released from the gut after eating that stimulates insulin secretion in a glucose-dependent way, suppresses glucagon, slows gastric emptying and reduces appetite. Approved GLP-1 receptor agonists are the basis of several diabetes and obesity medicines.
Lipolysis: The breakdown of stored triglycerides into fatty acids and glycerol for use as fuel. Increased lipolysis is not the same as fat loss, which depends on whether the released fatty acids are ultimately oxidised.
ROS: Reactive oxygen species — oxygen-containing molecules that readily react with cellular components. They cause oxidative damage in excess but also serve as normal signalling molecules, so suppressing them indiscriminately is not straightforwardly beneficial.

Cognitive

Anhedonia: Reduced ability to feel pleasure from activities that would normally be rewarding. It is a recognised symptom in depression and several other conditions, assessed clinically rather than by any biomarker.
BDNF: Brain-derived neurotrophic factor, a protein supporting neuron survival, growth and synaptic plasticity. It is frequently measured as a surrogate marker in cognitive research; a change in BDNF is not itself a change in cognition.
NGF: Nerve growth factor, a neurotrophin required for the survival and maintenance of certain sensory and sympathetic neurons. It was the first neurotrophic factor identified.
Synaptogenesis: The formation of new synapses between neurons. It occurs throughout life, not only during development, and underlies much of what is meant by neuroplasticity.
TBI: Traumatic brain injury — an injury to the brain caused by an external force, ranging from concussion to severe injury. Recovery trajectories vary widely, which makes small uncontrolled studies in this area particularly hard to interpret.

Bioregulators

Bioregulator: A term used for a family of very short peptides, mostly two to four amino acids, developed largely in Russian research and proposed to act on tissue-specific gene expression. The concept originates in a specific research tradition and is not an established pharmacological class internationally; supporting evidence is mostly published outside the mainstream English-language literature.

Longevity

Apoptosis: Programmed cell death — an orderly, energy-dependent process by which a cell dismantles itself without spilling its contents and provoking inflammation, in contrast to necrosis.
SASP: The senescence-associated secretory phenotype — the mix of inflammatory cytokines, growth factors and proteases released by senescent cells, through which a relatively small number of cells can affect surrounding tissue.
Senescent cell: A cell that has permanently stopped dividing but has not died, and which often secretes inflammatory signals. Accumulation of these cells with age is a leading hypothesis in ageing biology.
Senolytic: An agent intended to selectively eliminate senescent cells. The approach is under active investigation; no senolytic is approved for an ageing-related indication.

Immune

GALT: Gut-associated lymphoid tissue — the immune tissue of the intestinal wall, including Peyer's patches. It represents a large share of the body's immune cells and is where gut and immune function most directly meet.
Hashimoto's thyroiditis: An autoimmune disease in which the immune system attacks the thyroid gland, commonly leading to hypothyroidism. It is usually identified by thyroid antibodies together with thyroid function tests, and treated by replacing the missing hormone.
Herxheimer reaction: A short-lived worsening of symptoms with fever and chills after starting antimicrobial treatment, classically described in syphilis and other spirochaetal infections and attributed to the release of bacterial components. The term is often borrowed to explain feeling worse after starting an unrelated supplement or peptide, where it has no established basis.
Leaky gut: A popular term for increased intestinal permeability. Increased permeability is a real, measurable phenomenon observed in conditions such as coeliac disease and inflammatory bowel disease. What remains unsettled is the wider claim that it independently causes a broad range of unrelated systemic symptoms — that is a hypothesis, not established clinical fact.
MCAS: Mast cell activation syndrome — repeated episodes of mast-cell mediator release affecting multiple organ systems. Formal diagnostic criteria exist and require objective evidence such as a rise in serum tryptase during an episode; the label is applied far more often in practice than those criteria are met.
T-reg cells: Regulatory T cells, a subset of T lymphocytes that restrain immune responses and help maintain tolerance to the body's own tissues. Too little regulation permits autoimmunity; too much can blunt useful responses.