Knowledge Base

Hormone Therapy Glossary

62+ terms defined. From half-life to HPTA axis, every concept you need to understand hormone optimization, TRT protocols, and peptide therapy.

Medical Disclaimer

This content is for educational purposes only and is not medical advice. Always consult a qualified healthcare provider before starting any hormone therapy or peptide protocol. Never self-prescribe or adjust dosages without professional guidance.

A

Andropause: The gradual decline of male hormones, particularly testosterone, that occurs with aging. Unlike menopause in women, andropause is a slow, continuous decline rather than an abrupt shift. Also called late-onset hypogonadism or testosterone deficiency syndrome.
Aromatase: An enzyme (CYP19A1) that converts testosterone into estradiol (estrogen). Found in adipose tissue, brain, and other tissues. Higher body fat means more aromatase activity, which means more testosterone is converted to estrogen.
Aromatase Inhibitor (AI): A class of drugs (e.g., anastrozole/Arimidex) that block the aromatase enzyme, reducing the conversion of testosterone to estrogen. Used in TRT to manage elevated estradiol levels. Should only be used when bloodwork confirms elevated E2 with symptoms.

B

Bacteriostatic Water (BAC Water): Sterile water containing 0.9% benzyl alcohol as a preservative. Used to reconstitute lyophilized (freeze-dried) peptides. The benzyl alcohol prevents bacterial growth, giving reconstituted peptides a longer shelf life (typically 28-42 days) compared to sterile water.
Bioavailability: The proportion of a compound that enters systemic circulation and is available to have a biological effect. For example, oral testosterone has lower bioavailability than injectable testosterone because it must pass through the liver (first-pass metabolism).
Bioavailable Testosterone: The sum of free testosterone and albumin-bound testosterone. This represents the testosterone that is actually available for biological activity, as opposed to tightly bound testosterone attached to SHBG.
BPC-157: Body Protection Compound-157. A synthetic peptide derived from a sequence found in human gastric juice. Studied for its effects on tissue repair, angiogenesis, tendon and ligament healing, and gut health. One of the most widely used healing peptides.

C

CBC (Complete Blood Count): A blood test that measures red blood cells, white blood cells, hemoglobin, hematocrit, and platelets. Critical for TRT monitoring because testosterone can increase red blood cell production (erythropoiesis), potentially raising hematocrit to dangerous levels.
CJC-1295: A synthetic growth hormone-releasing hormone (GHRH) analog. Available with DAC (Drug Affinity Complex) for sustained release, or without DAC (also called Modified GRF 1-29) for shorter-acting pulses. Commonly stacked with Ipamorelin.
CMP (Comprehensive Metabolic Panel): A blood test that measures glucose, electrolytes, calcium, kidney function markers (BUN, creatinine), and liver function markers (AST, ALT, ALP, bilirubin). Used to monitor overall metabolic health during hormone therapy.
COA (Certificate of Analysis): A document provided by a testing laboratory that verifies the identity, purity, and potency of a compound. A legitimate COA should include HPLC analysis showing purity percentage (98%+ is standard), mass spectrometry confirming molecular identity, and endotoxin testing.
Compounding Pharmacy: A pharmacy that creates customized medications per a physician's prescription. 503A pharmacies compound for individual patients; 503B pharmacies compound in bulk under stricter FDA oversight. Compounding pharmacies are a common source for testosterone cream and many peptides.
Cortisol: The primary stress hormone, produced by the adrenal glands. Essential in acute stress responses, but chronically elevated cortisol suppresses the HPTA axis, reduces testosterone production, promotes visceral fat storage, and impairs sleep quality and immune function.
Cypionate (Testosterone Cypionate): A long-acting testosterone ester with a half-life of approximately 8 days. The most commonly prescribed form of injectable testosterone in the United States. Typically injected 2-3 times per week for stable blood levels.

D

DAC (Drug Affinity Complex): A chemical modification added to CJC-1295 that dramatically extends its half-life from approximately 30 minutes to 6-8 days by binding to albumin in the blood. CJC-1295 with DAC provides sustained GH elevation rather than pulsatile release.
DHEA (Dehydroepiandrosterone): A precursor hormone produced by the adrenal glands that can be converted into both testosterone and estrogen. DHEA peaks around age 25 and declines steadily. Some TRT protocols include supplemental DHEA to support adrenal pathways.
DHT (Dihydrotestosterone): A potent androgen converted from testosterone by the enzyme 5-alpha reductase. DHT is responsible for male-pattern hair growth, prostate growth, and some aspects of sexual function. Elevated DHT can accelerate hair loss in genetically predisposed men.

E

E2 (Estradiol): The primary form of estrogen in men. Produced through aromatization of testosterone. Essential for bone health, cardiovascular function, libido, and cognitive function, but excessive levels can cause water retention, mood issues, and gynecomastia. The sensitive assay (LC/MS-MS) should be used for accurate measurement in men.
Enanthate (Testosterone Enanthate): A long-acting testosterone ester with a half-life of approximately 7-8 days. The most commonly prescribed form of injectable testosterone globally. Functionally very similar to testosterone cypionate.
Enclomiphene: The trans-isomer of clomiphene citrate. A selective estrogen receptor modulator (SERM) that blocks estrogen at the hypothalamus, increasing GnRH, LH, and FSH, thereby stimulating natural testosterone production without suppressing the HPTA axis. Used as a TRT alternative or alongside TRT for fertility preservation.
Epitalon: A synthetic tetrapeptide (Ala-Glu-Asp-Gly) studied for its potential effects on telomerase activation and telomere length. Part of the longevity peptide category. Research is primarily from Russian studies; large-scale human clinical trials are limited.
Erythropoiesis: The production of red blood cells. Testosterone stimulates erythropoiesis, which is why hematocrit (red blood cell percentage) must be monitored during TRT. Elevated hematocrit increases blood viscosity and cardiovascular risk.
Ester: A chemical modification attached to a hormone molecule that controls its release rate into the bloodstream. Longer esters (like undecanoate) release more slowly, requiring less frequent injection. Shorter esters (like propionate) release quickly. The ester adds molecular weight, which means not all of the injected weight is active testosterone.

F

Free Testosterone: Testosterone that is not bound to any protein (SHBG or albumin) and is immediately available for biological activity. Represents approximately 1-3% of total testosterone. Considered by many practitioners to be a more clinically relevant marker than total testosterone alone.
FSH (Follicle-Stimulating Hormone): A gonadotropin released by the pituitary gland that stimulates Sertoli cells in the testes, supporting sperm production (spermatogenesis). FSH is suppressed by exogenous testosterone, which is why TRT typically reduces sperm count.

G

GHK-Cu: A copper peptide (glycyl-L-histidyl-L-lysine copper complex) that occurs naturally in human plasma. Promotes collagen synthesis, wound healing, tissue remodeling, anti-inflammatory effects, and skin regeneration. Available in injectable, topical, and cosmetic formulations.
GHRH (Growth Hormone-Releasing Hormone): A peptide hormone produced by the hypothalamus that stimulates the pituitary gland to release growth hormone. Synthetic GHRH analogs (like CJC-1295 and Sermorelin) are used in peptide therapy to enhance natural GH production.
GHRP (Growth Hormone-Releasing Peptide): A class of synthetic peptides that stimulate growth hormone release through the ghrelin receptor, independent of the GHRH pathway. Examples include Ipamorelin, GHRP-2, and GHRP-6. Often stacked with GHRH analogs for synergistic GH release.
GLP-1 (Glucagon-Like Peptide-1): A naturally occurring incretin hormone that stimulates insulin secretion, suppresses glucagon, slows gastric emptying, and reduces appetite. GLP-1 receptor agonists (semaglutide, tirzepatide) are prescription medications used for weight management and type 2 diabetes.
GnRH (Gonadotropin-Releasing Hormone): A hormone released by the hypothalamus in pulsatile bursts that signals the pituitary to release LH and FSH. GnRH is the master switch at the top of the HPTA axis. Its pulsatile pattern is critical; continuous GnRH exposure actually suppresses LH/FSH (the basis for GnRH agonist therapy).
Gynecomastia: The development of breast tissue in men, caused by an imbalance in the estrogen-to-androgen ratio. Can occur during TRT if estradiol rises too high relative to testosterone. Managed through dose adjustment, aromatase inhibitors, or in some cases SERMs.

H

Half-Life: The time it takes for half of a substance to be eliminated from the body. Important for determining injection frequency. Testosterone cypionate has a half-life of approximately 8 days, meaning after 8 days, half of the injected dose remains active.
HCG (Human Chorionic Gonadotropin): A peptide hormone that mimics LH (luteinizing hormone). Used in TRT protocols to maintain testicular function, intratesticular testosterone production, and fertility by keeping the Leydig cells stimulated despite HPTA suppression from exogenous testosterone. Typical dosing: 250-500 IU 2-3x per week.
Hematocrit: The percentage of blood volume occupied by red blood cells. Normal range for men is approximately 38-50%. TRT can increase hematocrit via erythropoiesis. Levels above 54% significantly increase risk of blood clots and cardiovascular events. Managed through dose reduction, increased hydration, therapeutic phlebotomy, or naringin supplementation.
HMG (Human Menopausal Gonadotropin): A medication containing both FSH and LH activity. Used in fertility protocols to directly stimulate both sperm production and testosterone synthesis. More potent than HCG alone for fertility restoration and often used when HCG alone is insufficient.
HPLC (High-Performance Liquid Chromatography): An analytical technique used to separate, identify, and quantify each component in a mixture. Used in COA testing to determine the purity of peptides and other compounds. A purity of 98% or higher is considered pharmaceutical grade.
HPTA (Hypothalamic-Pituitary-Testicular Axis): The hormonal feedback loop that controls testosterone production. The hypothalamus releases GnRH, the pituitary releases LH and FSH, and the testes produce testosterone. When testosterone is sufficiently high, the hypothalamus reduces GnRH. Exogenous testosterone suppresses this entire axis.
Hypogonadism: A medical condition in which the body does not produce enough testosterone. Primary hypogonadism originates in the testes (testicular failure); secondary hypogonadism originates in the hypothalamus or pituitary (signaling failure). Diagnosis requires low testosterone levels on at least two separate morning blood draws plus clinical symptoms.

I

IGF-1 (Insulin-Like Growth Factor 1): A hormone produced primarily by the liver in response to growth hormone. IGF-1 mediates most of GH's anabolic and reparative effects throughout the body. Serum IGF-1 levels are used as a proxy for growth hormone status because GH itself is released in pulses and is difficult to measure directly.
IM (Intramuscular): An injection delivered directly into muscle tissue using a longer needle (typically 1-1.5 inch, 22-25 gauge). Common IM injection sites include the ventrogluteal (hip), deltoid (shoulder), and vastus lateralis (outer thigh). Traditionally the standard for testosterone injections, though Sub-Q has become increasingly popular.
Ipamorelin: A selective growth hormone-releasing peptide (GHRP) that stimulates GH release by acting on the ghrelin receptor. Called the 'gentlest' GH secretagogue because it selectively increases GH without significantly affecting cortisol, prolactin, or appetite. Commonly stacked with CJC-1295 (no DAC).

K

KPV: A tripeptide (Lys-Pro-Val) that is a fragment of alpha-melanocyte-stimulating hormone (alpha-MSH). Has anti-inflammatory and antimicrobial properties. Studied for gut health, inflammatory conditions, and wound healing. Available in injectable, oral, and topical formulations.

L

LH (Luteinizing Hormone): A gonadotropin released by the pituitary gland that stimulates Leydig cells in the testes to produce testosterone. LH is the direct signal for testicular testosterone production and is suppressed when exogenous testosterone is introduced (via TRT).
Lyophilized: Freeze-dried. Most injectable peptides are shipped as a lyophilized powder that must be reconstituted with bacteriostatic water before injection. Lyophilization preserves the peptide's stability during shipping and storage at room temperature.

M

MK-677 (Ibutamoren): An oral growth hormone secretagogue that activates the ghrelin receptor to increase GH and IGF-1 levels. Not a peptide technically (it is a non-peptide GH secretagogue). Convenient (oral dosing) but can increase appetite, blood sugar, and water retention.

P

PCT (Post-Cycle Therapy): A protocol used to restart natural testosterone production after discontinuing exogenous testosterone or anabolic steroids. Typically involves SERMs (like Nolvadex or Clomid) and sometimes HCG to stimulate the HPTA axis to resume normal function.
Phlebotomy (Therapeutic): The medical procedure of removing blood to lower hematocrit levels. Essentially a blood donation. Used when TRT causes hematocrit to rise above safe levels (typically >52-54%). Some men on TRT need phlebotomy every 8-12 weeks.
Pregnenolone: A steroid hormone synthesized from cholesterol. Called the 'mother hormone' because it is the precursor from which nearly all other steroid hormones are derived, including DHEA, progesterone, cortisol, and testosterone. Some TRT protocols include supplemental pregnenolone.
Prolactin: A hormone produced by the pituitary gland. Elevated prolactin in men can suppress GnRH, reduce testosterone, and cause sexual dysfunction. Prolactin should be tested as part of initial hormone evaluation to rule out pituitary issues (prolactinoma).
Propionate (Testosterone Propionate): A short-acting testosterone ester with a half-life of approximately 2-3 days. Requires frequent injection (every other day or daily). Provides very stable blood levels but is less convenient. Sometimes used for initial dose-finding due to its rapid clearance.
PSA (Prostate Specific Antigen): A protein produced by the prostate. Elevated PSA can indicate prostate enlargement, inflammation, or cancer. PSA should be monitored before and during TRT. TRT does not cause prostate cancer but can stimulate growth of pre-existing cancer.

R

Reconstitution: The process of mixing a lyophilized (freeze-dried) peptide powder with bacteriostatic water to create an injectable solution. Proper reconstitution involves slowly adding BAC water down the side of the vial and gently swirling, never shaking.

S

Selank: A synthetic peptide analog of the naturally occurring immunomodulatory peptide tuftsin. Provides anxiolytic (anti-anxiety) effects, enhances cognitive function, and modulates the immune system. Often used alongside Semax. Administered as a nasal spray.
Semax: A synthetic peptide analog of ACTH (adrenocorticotropic hormone) fragment 4-10. Enhances BDNF (brain-derived neurotrophic factor) production. Used as a nootropic for cognitive enhancement, focus, and neuroprotection. Administered as a nasal spray.
SERM (Selective Estrogen Receptor Modulator): A class of drugs that selectively block or activate estrogen receptors in different tissues. Tamoxifen (Nolvadex) and Clomiphene (Clomid) are SERMs used in PCT and fertility protocols. They block estrogen at the hypothalamus, increasing GnRH and stimulating the HPTA axis.
SHBG (Sex Hormone-Binding Globulin): A protein produced by the liver that binds to testosterone, making it biologically inactive. High SHBG means less free (usable) testosterone. SHBG increases with age, thyroid hormones, and low insulin; it decreases with obesity, insulin resistance, and androgen use.
Sub-Q (Subcutaneous): An injection delivered into the fatty tissue just beneath the skin using a short, fine needle (typically 0.5 inch, 27-31 gauge insulin syringe). Increasingly popular for testosterone and peptide injections due to reduced pain, ease of self-administration, and potentially more stable absorption.

T

TB-500 (Thymosin Beta-4): A synthetic version of the naturally occurring peptide thymosin beta-4. Promotes cell migration, blood vessel formation, and tissue repair. Used for systemic healing, often stacked with BPC-157 for synergistic wound and tissue repair.
Tesamorelin: An FDA-approved GHRH analog (Egrifta). Originally indicated for HIV-related lipodystrophy. Increases GH secretion and has been shown to significantly reduce visceral adipose tissue. One of the few peptides with robust human clinical trial data.
Total Testosterone: The total amount of testosterone in the blood, including free testosterone, albumin-bound testosterone, and SHBG-bound testosterone. Standard lab reference range is approximately 264-916 ng/dL. Should always be interpreted alongside free testosterone and SHBG for a complete picture.
Trough Level: The lowest point of a hormone's concentration in the blood during a dosing cycle. For TRT, trough levels are measured just before the next injection to ensure levels remain adequate between doses. Bloodwork for TRT should be drawn at trough.

U

Undecanoate (Testosterone Undecanoate): A very long-acting testosterone ester. Available as an injectable (Aveed/Nebido) with a half-life of approximately 33 days, administered every 10-14 weeks. Also available orally (Jatenzo) and absorbed through the lymphatic system to bypass liver metabolism.