Glossary

Terms used across the compound library and the app, in plain English.

Anabolic–androgenic steroid

A synthetic substance related to testosterone. "Anabolic" refers to effects on muscle and bone, "androgenic" to male characteristics such as body hair and a deeper voice.

Androgen receptor

The protein inside cells that testosterone and related steroids bind to. Once bound, it switches certain genes on or off.

Aromatase

The enzyme that turns testosterone into oestradiol, a form of oestrogen. Aromatase inhibitors block it.

Ester

A chain attached to a hormone, such as testosterone cypionate or enanthate, that slows its release from an oil injection. The ester mainly changes how long a dose lasts, not what the hormone does.

FSH and LH

Follicle-stimulating hormone and luteinising hormone. Pituitary hormones that tell the testes or ovaries to make sex hormones and sperm or eggs. Testosterone from outside the body usually lowers both.

GLP-1 receptor agonist

A medicine that copies the gut hormone GLP-1. It increases insulin release after meals, slows stomach emptying and reduces appetite. Semaglutide and liraglutide are examples.

Haematocrit

The share of your blood made up of red blood cells, shown as a percentage or a fraction. Testosterone can raise it, which thickens the blood.

Half-life

The time it takes for the amount of a substance in the body to fall by half. After about five half-lives, almost all of a single dose is gone, and with regular doses levels have settled.

Hypogonadism

When the testes or ovaries make too little sex hormone. "Primary" means the problem is in the testes or ovaries; "secondary" or "hypogonadotropic" means the pituitary or brain isn't sending the signal.

IGF-1

Insulin-like growth factor 1. Made mainly in the liver in response to growth hormone, and the usual blood test for growth hormone activity.

Off-label use

When a doctor prescribes an approved medicine for a use that isn't in its licence. It's legal in many countries but means the use hasn't been through the same approval process.

Oestradiol (E2)

The main form of oestrogen. In men it's made mostly from testosterone by aromatase.

PSA

Prostate-specific antigen, a blood test used to watch the prostate in men on testosterone.

SERM

Selective oestrogen receptor modulator. A medicine that blocks oestrogen in some tissues and acts like it in others. Tamoxifen and clomifene are examples.

SHBG

Sex hormone-binding globulin, a protein that carries testosterone and oestradiol in the blood. Hormone bound to it isn't available to tissues.

Steady state

The point, after about five half-lives of regular doses, where the amount taken in matches the amount cleared, so levels rise and fall in the same pattern between doses.

Supraphysiological

Higher than the body would naturally produce.

Trough

The lowest level, just before the next dose.

Veterinary medicine

A medicine approved only for animals. Veterinary approval says nothing about safety in people.