[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Pharmacology](https://durgical.com/en/pharmacology/) › The hypothalamic–pituitary axis # The hypothalamic–pituitary axis How the hypothalamus and pituitary run the thyroid, adrenal, gonadal, growth and milk axes through feedback, and the drugs that act at each level. Updated Nov 2, 2026 The hypothalamus sends releasing and inhibiting hormones down a small portal blood system to the anterior pituitary, which then drives peripheral glands. The posterior pituitary releases vasopressin and oxytocin made by hypothalamic neurons. Negative feedback from the end hormone keeps each axis in balance, and most endocrine drugs either replace a missing hormone, block an excess one or use feedback on purpose. ## Key points - Hypothalamic hormones: TRH, CRH, GnRH, GHRH, somatostatin (inhibits GH and TSH) and dopamine (inhibits prolactin). - Anterior pituitary hormones: TSH, ACTH, LH, FSH, GH and prolactin; posterior pituitary: vasopressin (ADH) and oxytocin. - End hormones (thyroid hormone, cortisol, sex steroids, IGF-1) feed back to suppress the hypothalamus and pituitary. - GnRH works only when released in pulses: continuous GnRH agonists first stimulate, then shut down the gonadal axis, which is used in prostate cancer and other conditions. - Long-term glucocorticoids suppress CRH and ACTH; stopping them suddenly can cause adrenal insufficiency. ## The axes at a glance - Thyroid: TRH → TSH → T4/T3 - Adrenal: CRH → ACTH → cortisol - Gonadal: GnRH → LH and FSH → testosterone, oestradiol, progesterone - Growth: GHRH (+) and somatostatin (−) → GH → IGF-1 from the liver - Prolactin: dopamine is the main brake - Posterior pituitary: vasopressin (water balance) and oxytocin (labour, milk ejection) ## Using feedback in diagnosis and treatment Hormone pairs are read together: in primary hypothyroidism TSH is high and T4 low, while in pituitary disease both are low. Levothyroxine replacement is adjusted by TSH in primary hypothyroidism. Dexamethasone suppresses ACTH in normal people but not in most ACTH-independent or ectopic cortisol excess, which makes it a diagnostic test. Metyrapone blocks cortisol synthesis and is used to treat or test the adrenal axis. ## Drugs at each level - GnRH agonists (leuprorelin, goserelin): continuous exposure down-regulates the pituitary, after an initial «flare»; GnRH antagonists (degarelix) suppress at once with no flare - Somatostatin analogues (octreotide): lower GH in acromegaly and hormone release from some neuroendocrine tumours - Somatropin: recombinant GH for proven GH deficiency - Dopamine agonists (cabergoline, bromocriptine): shrink prolactinomas and lower prolactin - Desmopressin: V2 agonist for central diabetes insipidus - Oxytocin: induces or strengthens labour and prevents postpartum haemorrhage; a high-alert medicine ## Suppression by treatment Any exogenous end hormone can switch off its own axis. Glucocorticoids given for weeks or more suppress the adrenal axis, so they are tapered rather than stopped, and patients may need extra cover during illness or surgery. Excess thyroid hormone suppresses TSH; anabolic steroids and testosterone suppress LH, FSH and sperm production. Pituitary failure (hypopituitarism) is treated by replacing the end hormones, with cortisol replaced before thyroid hormone. ## Memory aid «Pulse to push, constant to stop»: pulsed GnRH stimulates the gonads; continuous GnRH agonists shut them down. ## Test yourself Think of the answer, then tap the question to see it. ## Why does continuous leuprorelin lower testosterone even though it is a GnRH agonist? GnRH receptors respond only to pulses; constant stimulation desensitises and down-regulates them, so LH and FSH fall after an initial flare. ## Which hypothalamic signal is the main inhibitor of prolactin, and which drugs copy it? Dopamine, acting on D2 receptors; dopamine agonists such as cabergoline and bromocriptine copy it. ## Why are long courses of prednisone tapered instead of stopped abruptly? They suppress CRH and ACTH; the adrenal glands need time to recover, and sudden withdrawal can cause adrenal insufficiency. ## In hypopituitarism, why is cortisol replaced before thyroid hormone? Thyroid hormone speeds cortisol clearance and metabolism; giving it first can precipitate an adrenal crisis when cortisol is already low. [Add to my cards (4)](https://durgical.app/estudiar/?add=/en/pharmacology/topics/the-hypothalamic-pituitary-axis/) [More Pharmacology questions →](https://durgical.com/en/practice/?f=pharmacology) ## Example drugs - [Somatropin](https://durgical.com/en/pharmacology/somatropin/) - [Octreotide](https://durgical.com/en/pharmacology/octreotide/) - [Desmopressin](https://durgical.com/en/pharmacology/desmopressin/) - [Leuprorelin](https://durgical.com/en/pharmacology/leuprorelin/) - [Goserelin](https://durgical.com/en/pharmacology/goserelin/) - [Degarelix](https://durgical.com/en/pharmacology/degarelix/) - [Cabergoline](https://durgical.com/en/pharmacology/cabergoline/) - [Bromocriptine](https://durgical.com/en/pharmacology/bromocriptine/) - [Oxytocin](https://durgical.com/en/pharmacology/oxytocin/) - [Levothyroxine](https://durgical.com/en/pharmacology/levothyroxine/) - [Hydrocortisone](https://durgical.com/en/pharmacology/hydrocortisone/) - [Prednisone](https://durgical.com/en/pharmacology/prednisone/) - [Dexamethasone](https://durgical.com/en/pharmacology/dexamethasone/) - [Metyrapone](https://durgical.com/en/pharmacology/metyrapone/) ## Connections ## Related classes 10 - [Growth hormone](https://durgical.com/en/pharmacology/classes/growth-hormone/) - [Somatostatin analogues](https://durgical.com/en/pharmacology/classes/somatostatin-analogues/) - [Vasopressin and its analogues](https://durgical.com/en/pharmacology/classes/vasopressin-and-its-analogues/) - [GnRH analogues (agonists and antagonists)](https://durgical.com/en/pharmacology/classes/gnrh-analogues/) - [Dopamine agonists](https://durgical.com/en/pharmacology/classes/dopamine-agonists/) - [Uterotonics (oxytocin and analogues)](https://durgical.com/en/pharmacology/classes/uterotonics/) - [Corticosteroids (glucocorticoids)](https://durgical.com/en/pharmacology/classes/corticosteroids/) - [Thyroid hormones](https://durgical.com/en/pharmacology/classes/thyroid-hormones/) - [Antithyroid agents](https://durgical.com/en/pharmacology/classes/antithyroid-agents/) - [Adrenal steroid synthesis inhibitors](https://durgical.com/en/pharmacology/classes/adrenal-steroid-synthesis-inhibitors/) [← All of pharmacology](https://durgical.com/en/pharmacology/) Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given. Sources: [Hypopituitarism: MedlinePlus Medical Encyclopedia](https://medlineplus.gov/ency/article/000343.htm) (MedlinePlus (U.S. National Library of Medicine), 2026); [Pituitary & Pineal Glands](https://training.seer.cancer.gov/anatomy/endocrine/glands/pituitary.html) (National Cancer Institute, SEER Training Modules, 2026). ## **Spotted a mistake?** We are always improving for the community. Tell us what is wrong and our team will review it. Report a mistake Representative model, for educational purposes only. --- Source: https://durgical.com/en/pharmacology/topics/the-hypothalamic-pituitary-axis/ License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/pharmacology/topics/the-hypothalamic-pituitary-axis/