Tissue

Stores fat and houses most of the body's aromatase, so more fat mass means more conversion of androgen to estrogen.

Makes cortisol and the adrenal androgens. It answers to ACTH from the pituitary rather than to LH, which is why shutting down the testicular axis leaves it running.

The threat detector. Dense in androgen receptors, and the structure most implicated in the anger, vigilance and fear side of what these compounds do. Splitting it out of the limbic system matters because threat processing and reward processing sit in the same blob otherwise, and compounds pull them in opposite directions.

The gland that actually releases growth hormone, LH and FSH. Every GH secretagogue and every GnRH drug is aimed here, not at the tissue where the effect is finally felt.

Where red cells are built. Androgens push it harder, which is why they were once a treatment for anaemia and why haematocrit climbs on cycle.

Responds to both estrogen and prolactin. Once glandular tissue forms it does not go away on its own, which is why this one is worth preventing rather than treating.

The lining of the airways. It is the target of the lung bioregulators and one of the tissues VIP acts on.

Joint surface tissue with almost no blood supply, which is why it repairs so slowly and why it is targeted separately from tendon.

The single cell layer separating gut contents from the bloodstream. Most peptides sold for gut health are aimed at either repairing it or keeping its tight junctions shut.

Carries androgen receptors like skeletal muscle does, and thickens under the same signal. Unlike a bicep, a thicker left ventricle fills less well.

Where new memory is laid down. Unusually sensitive to sustained cortisol and to lost deep sleep, both of which these compounds can produce, which makes it the structure behind most reported memory complaints.

The control room above the pituitary. Appetite, body temperature, the reproductive axis and the GH rhythm are all set here, which is why so many peptides that produce whole-body effects act on one small area.

Controls sodium and water balance and produces erythropoietin, so it sits behind both the bloat and the rising red cell count.

The testicular cells that actually make testosterone in response to LH. Anything that restarts the axis has to reach these; anything that shuts the axis down starves them.

The emotional core of the brain, and androgen-receptor rich. This is where mood, threat response and aggression are set, and where steroid mental effects are thought to land.

Processes every oral steroid on first pass. The 17-alpha-alkyl group that lets an oral survive that trip is also what makes it hard on this organ.

The insulin and glucagon-producing cells. Incretin drugs raise insulin here only when glucose is already high, which is why they do not cause hypoglycaemia on their own the way injected insulin does.

The gland that makes melatonin and sets the day-night rhythm. The Russian bioregulator peptides are aimed at it on the theory that restoring that rhythm slows other ageing processes.

Planning, judgement and the brake on impulse. Relevant here because the reported behaviour change on these compounds is often better described as a weaker brake than as a stronger drive, and those two have different consequences.

Growth here is driven mainly by DHT rather than testosterone, which is why compounds that resist 5-alpha-reductase are gentler on it.

In a genetically susceptible scalp, DHT binding shrinks the follicle a little with each cycle. The predisposition is inherited; the androgen sets the pace.

Oil glands in the skin. Androgen signalling raises output, and heavier oil plus keratin plugging is how steroid acne starts.

The intended target. Dense in androgen receptors, and the tissue where the whole risk trade is being made.

The largest organ, and the target for the melanocortin and copper peptides. Pigment, collagen and wound repair all happen here.

Where ghrelin is produced and where GLP-1 agonists slow emptying. That slowing is both the satiety mechanism and the source of the nausea.

Connective tissue adapts far slower than muscle. A strength jump that outpaces it is the setup for a tear.

Makes testosterone and sperm, and needs LH and FSH from the pituitary to do either. Cut that signal and it shrinks and goes quiet.

Where T-cells mature. It shrinks steadily with age, which is the premise behind every thymic peptide: restore the training ground rather than the cells.

The single-cell lining of every blood vessel. It sets vessel tone and is where plaque begins when lipids and pressure both move the wrong way.