Glossary of Terms

A

AA — Anti-androgen. A medication that blocks or reduces the effects of testosterone.

AFAB — Assigned Female At Birth.

ALT / AST — Alanine transaminase and aspartate transaminase. Liver enzymes measured in a blood test to monitor liver function (see LFT).

AMAB — Assigned Male At Birth.

Androgen — A hormone that promotes masculine characteristics, e.g., testosterone and DHT.

Aromatase — An enzyme that converts testosterone into estradiol.

Aromatase inhibitor — A medication (anastrozole, letrozole) that blocks aromatase, reducing conversion of T to E2.

B

Bica / Bicalutamide — A non-steroidal androgen receptor blocker used as an anti-androgen in feminising HRT.

Bioavailability — The fraction of a drug that reaches systemic circulation unchanged. Routes with higher bioavailability (injections, sublingual) require lower doses than oral.

Bioidentical — Chemically identical to hormones naturally produced by the human body (e.g., 17β-estradiol, bioidentical progesterone). Distinct from synthetic analogues like ethinylestradiol.

Bottom growth — Clitoral enlargement caused by testosterone therapy.

Buccal — Absorbed through the gum or cheek lining (e.g., buccal testosterone tablets).

Buserelin — A GnRH agonist used as an anti-androgen, typically administered as a nasal spray.

C

Carrier oil — The oil (MCT, grapeseed, sesame, etc.) in which injectable hormones are dissolved.

CBC — Complete blood count. A blood test measuring red blood cells, white blood cells, and platelets.

Cisgender — A person whose gender identity aligns with the sex they were assigned at birth.

CMP — Comprehensive metabolic panel. A blood test measuring liver enzymes, kidney function, and electrolytes.

Contraindication — A condition or factor that makes a particular treatment inadvisable.

CPA / Cyproterone acetate — A progestogenic anti-androgen that suppresses testosterone production; used mainly outside the US.

Counterfeit — Fake or adulterated medication, often under-dosed, over-dosed, or contaminated.

Cypionate — An ester (e.g., testosterone cypionate, estradiol cypionate) that slows hormone release, allowing less frequent dosing.

D

DHT — Dihydrotestosterone. A potent androgen converted from testosterone; linked to hair loss and bottom growth.

DIY — Do-It-Yourself. Obtaining and managing HRT without a prescription or medical supervision.

DVT — Deep vein thrombosis. A blood clot in a deep vein, usually in the leg; can travel to the lungs (see PE).

E

E1 / Estrone — A weak estrogen produced mainly by the liver from oral estradiol. High E1:E2 ratios are a known effect of oral administration.

E2 / Estradiol — The primary active form of estrogen in the body; also called 17β-estradiol. This is the main hormone used in feminising HRT.

EC — Estradiol cypionate. An injectable estradiol ester with a half-life of 5–7 days.

EEn — Estradiol enanthate. An injectable estradiol ester with a half-life of 7–10 days.

Enanthate — An ester (e.g., estradiol enanthate, testosterone enanthate) that slows hormone release for weekly or longer dosing intervals.

Endocrine Society — A professional medical organisation whose 2017 clinical practice guideline is the most widely cited reference for gender-affirming hormone therapy.

Estrogen — A class of hormones that promote feminine characteristics. The primary estrogen in HRT is 17β-estradiol (see E2).

EV — Estradiol valerate. An injectable estradiol ester with a half-life of 4–5 days (dosed every 5 days).

F

Filter / 0.22 μm syringe filter — A sterile single-use filter that removes bacteria, fungal spores, and particulates from injectable solutions. Mandatory for homebrew injectables; not needed for sealed pharmaceutical vials.

First-pass metabolism — The processing of an orally ingested drug by the liver before it reaches systemic circulation. Oral estrogen undergoes extensive first-pass, increasing VTE risk and producing unfavourable E1:E2 ratios. Sublingual, transdermal, and injectable routes bypass first-pass.

Free T — Testosterone not bound to SHBG; the biologically active fraction of total testosterone.

FSH — Follicle-stimulating hormone. Part of the HPG axis; suppressed by exogenous sex hormones.

G

GAHT — Gender-Affirming Hormone Therapy (also called HRT). The use of hormones to align secondary sex characteristics with gender identity.

GnRH — Gonadotropin-releasing hormone. The hypothalamic hormone that controls LH and FSH release.

GnRH agonist / Puberty blocker — A medication (leuprolide, goserelin, buserelin) that suppresses LH and FSH by overstimulating the pituitary, effectively shutting down gonadal hormone production. Used in adolescents and adults.

H

HCT / Hematocrit — The percentage of red blood cells in blood. Monitored in testosterone therapy because elevated T can raise HCT (see Polycythemia).

Hepatotoxicity — Liver toxicity. A rare but serious risk of some medications used in HRT (bicalutamide, CPA, oral estrogen at very high doses).

Homebrew — Hormone medications (typically injectable estradiol) made by community members rather than pharmaceutical companies. Requires additional safety precautions including 0.22 μm filtration.

Hormone — A chemical messenger produced by endocrine glands that travels through the bloodstream to regulate bodily functions (growth, metabolism, reproduction, etc.).

HPG axis — Hypothalamus–Pituitary–Gonadal axis. The feedback loop that controls sex hormone production. HRT works by altering signals in this axis.

HPLC — High-performance liquid chromatography. A laboratory method used to verify the exact concentration of active ingredient in a medication sample (gold standard for testing homebrew and counterfeits).

HRT — Hormone Replacement (or Hormone Therapy) / Gender-Affirming Hormone Therapy (see GAHT).

Hyperkalemia — Abnormally high potassium levels in the blood. A potential side effect of spironolactone, especially when combined with NSAIDs, ACE inhibitors, or kidney disease.

I

IM — Intramuscular. An injection delivered deep into a muscle (e.g., gluteal, thigh).

Informed consent — A model of care where treatment begins after the patient signs a document acknowledging the known risks, without requiring a referral letter from a mental health provider.

Injection — Administration of medication via a needle and syringe. Routes include intramuscular (IM) and subcutaneous (SC/SubQ).

L

LFT — Liver function test (see ALT, AST). Blood tests that measure liver health, typically ALT and AST.

LH — Luteinising hormone. Stimulates testosterone production in the testes; suppressed by estrogen therapy.

Lipid panel — A blood test measuring cholesterol (HDL, LDL) and triglycerides. Monitored because some HRT routes affect lipid profiles.

M

MCT oil — Medium-chain triglyceride oil. A common carrier oil in homebrew injectables, valued for its low viscosity and stability.

Meningioma — A (usually benign) brain tumour associated with high cumulative doses of CPA. Risk increases with dose and duration of use.

Metoidioplasty — A surgical procedure that releases the clitoris to create a small phallus; often pursued by trans masculine individuals on T.

Monotherapy — Using estrogen alone (without an anti-androgen) at sufficient doses to suppress testosterone via HPG axis feedback.

N

NSAIDs — Non-steroidal anti-inflammatory drugs (ibuprofen, naproxen, etc.). Can worsen kidney function and raise potassium when combined with spironolactone.

P

P4 / Progesterone — A hormone involved in menstrual cycles and pregnancy. Used by some trans women for breast maturation, libido, and mood; also used by trans masculine individuals for bleeding control.

PE — Pulmonary embolism. A blood clot in the lungs, often originating from a DVT. Life-threatening; requires emergency treatment.

Pellets — Subcutaneous hormone implants (typically estradiol or testosterone) that release hormone steadily over several months.

Polycythemia — An elevated red blood cell count. In the context of T therapy, this specifically refers to secondary erythrocytosis (rising haematocrit from testosterone-stimulated erythropoiesis), which is distinct from polycythemia vera (a bone marrow disorder).

Prolactin — A hormone that can become elevated with CPA use. High prolactin may cause galactorrhea (lactation), low libido, and headaches.

Puberty blocker — See GnRH agonist.

R

Relugolix — A GnRH antagonist used as an anti-androgen. Unlike GnRH agonists, it does not cause an initial testosterone flare. Taken orally once daily.

S

SC / SubQ — Subcutaneous. An injection delivered into the layer of fat under the skin, typically using a shorter, thinner needle than IM.

SHBG — Sex hormone-binding globulin. A protein that binds to sex hormones, regulating the amount of free (biologically active) hormone. High SHBG can reduce the effectiveness of HRT, especially with oral estrogen.

SOC / Standards of Care — Clinical guidelines published by WPATH (currently Version 8, 2022) for the health of transgender and gender-diverse people.

Spiro / Spironolactone — A potassium-sparing diuretic used as an anti-androgen, primarily in the US. Blocks androgen receptors and mildly suppresses T production.

Sterile technique — A set of practices (cleaning vial septa with alcohol, using sterile needles, not reusing syringes) used to prevent contamination during injections.

Sublingual — A route of administration where a tablet is held under the tongue to dissolve, allowing direct absorption into the bloodstream. Avoids first-pass liver metabolism.

T

T — Testosterone. The primary androgen; used in masculinising HRT; suppressed in feminising HRT.

Tanner stage — A scale (1–5) describing progression through puberty. Used to determine appropriate starting doses for adolescent HRT.

Transdermal — Absorption through the skin (e.g., patches, gel). Avoids first-pass metabolism; lower VTE risk than oral routes.

Transfeminine / Trans femme — A person assigned male at birth who identifies with a feminine gender identity. Used as an umbrella term.

Transmasculine / Trans masc — A person assigned female at birth who identifies with a masculine gender identity. Used as an umbrella term.

Trough — The lowest point of hormone levels in a dosing cycle (measured just before the next dose). The most clinically useful time to test blood levels.

U

Undecylate — An ester (e.g., estradiol undecylate, EUn) with a long half-life of 12–16 days, allowing dosing every 2–4 weeks.

V

Valerate — An ester (e.g., estradiol valerate, EV) that slows hormone release for multi-day dosing intervals (typically every 5 days for EV).

Vial — A small glass bottle with a rubber septum that contains injectable medication. Vials are sealed with a metal crimp cap.

VTE — Venous thromboembolism. A collective term for DVT and PE; the most well-known risk of estrogen therapy, especially oral.

W

WPATH — World Professional Association for Transgender Health. An international organisation that publishes the Standards of Care (SOC) for transgender health, currently in Version 8 (2022).