- Amino acid
- The basic building block of peptides and proteins. There are 20 standard amino acids; their order in a chain determines what a peptide does.
- Peptide bond
- The chemical bond that links amino acids together into a chain.
- Peptide vs. protein
- Both are amino-acid chains. Peptides are short (roughly 2–50 amino acids); proteins are long, folded chains of many more.
- Analog
- A modified version of a natural peptide, engineered to change its strength, duration, or selectivity — for example, a longer-acting version of a natural hormone.
- Receptor agonist
- A molecule that activates a receptor, switching on its signal (e.g. a GLP-1 receptor agonist mimics the hormone GLP-1).
- Receptor antagonist
- A molecule that blocks a receptor, preventing its normal signal (e.g. a GnRH antagonist).
- GLP-1
- Glucagon-like peptide-1 — a gut hormone that curbs appetite and improves insulin response. The target of weight-loss/diabetes drugs like semaglutide.
- GIP
- Glucose-dependent insulinotropic polypeptide — a second incretin hormone, combined with GLP-1 in dual agonists like tirzepatide.
- Incretin
- A gut hormone (such as GLP-1 or GIP) released after eating that boosts insulin and reduces appetite. 'Incretin mimetics' copy them.
- Secretagogue
- A substance that prompts the body to secrete something — e.g. a growth-hormone secretagogue triggers release of the body's own growth hormone.
- GHRP
- Growth-hormone-releasing peptide — acts on the ghrelin receptor to trigger a growth-hormone pulse (e.g. ipamorelin).
- GHRH analog
- A peptide modeled on growth-hormone-releasing hormone that stimulates the pituitary (e.g. sermorelin, CJC-1295).
- IGF-1
- Insulin-like growth factor 1 — a hormone downstream of growth hormone that drives tissue and muscle growth.
- Myostatin
- A protein that limits muscle growth; some experimental peptides aim to inhibit it to promote muscle.
- Melanocortin system
- A brain/skin signaling system involved in pigmentation and sexual desire — the target of peptides like PT-141 and melanotan.
- GnRH
- Gonadotropin-releasing hormone — the master switch of the reproductive hormone cascade. Agonists and antagonists are used in fertility and cancer care.
- Nootropic
- A substance studied for cognitive benefits (memory, focus). Several neuropeptides such as Semax are described this way.
- Bioregulator
- A term for ultra-short synthetic peptides (often of Russian origin) proposed to influence specific tissues; evidence is largely preclinical.
- Subcutaneous
- Injection into the fat layer just under the skin — the most common route for peptide injections.
- Bioavailability
- The fraction of a dose that reaches the bloodstream intact. Most peptides have very low oral bioavailability because they're digested.
- Half-life
- How long it takes for half of a substance to clear from the body — a key driver of how often a peptide must be dosed.
- Research chemical
- A compound sold 'for research use only' that is not approved for human use and often lacks human safety or efficacy data.
- FDA
- The U.S. Food and Drug Administration — the regulator that approves medicines and polices unapproved drug marketing.
- WADA
- The World Anti-Doping Agency, whose code prohibits many peptides in sport at all times.
Frequently asked questions
What does 'secretagogue' mean for peptides?
A secretagogue is something that makes the body secrete a substance. Growth-hormone secretagogues — like GHRPs and GHRH analogs — prompt the pituitary to release the body's own growth hormone rather than injecting it directly.
What is the difference between a receptor agonist and antagonist?
An agonist activates a receptor and switches its signal on; an antagonist blocks the receptor and prevents its signal. For example, a GLP-1 receptor agonist mimics GLP-1, while a GnRH antagonist blocks GnRH signaling.
What does 'research use only' mean?
It is a label on peptides sold as laboratory reagents rather than approved medicines. Such compounds are not approved for human use and are generally not quality-assured.
Keep exploring: Semaglutide · Ipamorelin · PT-141 · Weight Loss & Metabolic · Sexual Health · More guides →