How the brain controls the body's hormone system through the hypothalamus and pituitary — and how hormones such as cortisol, oxytocin, sex hormones, thyroid hormone and melatonin act back on the brain.
Neurotransmitters & Brain Chemistry
Intermediate
Hormones and the Brain
The Editors
October 29, 2025
2 min read
In plain English
Hormones are chemical messengers carried in the blood. The brain controls most of the hormone system through the hypothalamus and pituitary gland — and hormones in turn change how the brain works, affecting stress, sleep, growth, mood and behaviour.
Intermediate level: Builds on the basics. Introduces the real vocabulary and the mechanisms behind it.
Concepts to know first
The nervous system and the endocrine (hormone) system are the body's two great communication networks. Nerves are fast and targeted; hormones are slower and broadcast through the blood. They are tightly linked, and the brain sits at the top.
The master controls
The hypothalamus, an almond-sized region at the base of the brain, releases hormones that control the pituitary gland just below it. The pituitary in turn releases hormones that regulate the thyroid, adrenal glands, ovaries and testes, growth and milk production. Two hormones — oxytocin and vasopressin — are made by hypothalamic neurons and released directly from the back of the pituitary. This chain of command is called an axis.
The stress axis
The best-studied chain is the hypothalamic–pituitary–adrenal (HPA) axis. Under stress, the hypothalamus releases CRH, the pituitary releases ACTH, and the adrenal glands release cortisol. Cortisol mobilises energy and dampens inflammation — and feeds back on the brain, including the hippocampus, to switch the response off. Chronic stress can disrupt this feedback.
Hormones that change the brain
Oxytocin acts on brain circuits for social bonding, trust and maternal behaviour (though popular claims of a "love hormone" are oversimplified). Vasopressin controls water balance and also influences social behaviour. Sex hormones — oestrogen, progesterone and testosterone — shape brain development and influence mood, memory and behaviour across life; shifts around puberty, pregnancy and menopause can affect the brain. Thyroid hormone is essential for brain development: untreated deficiency in infancy causes severe intellectual disability, which is why newborns are screened. Melatonin, from the pineal gland, signals darkness and helps time sleep.
Gut and fat talk to the brain
Hormones from outside the classic glands also reach the brain: leptin from fat cells signals energy stores, ghrelin from the stomach signals hunger, and GLP-1 from the gut signals fullness — the basis for a new generation of weight-loss drugs.
Everyday examples & things to try
Analogy
Email versus broadcast
Nerves are like emails to specific people: fast and targeted. Hormones are like a radio broadcast: slower, but heard by every cell with the right receiver. The hypothalamus runs the radio station.
Key takeaways
- The hypothalamus controls the pituitary, the 'master gland' of the hormone system.
- The HPA axis (CRH → ACTH → cortisol) drives the stress response, with feedback to the brain.
- Hormones such as oxytocin, sex hormones, thyroid hormone, melatonin, leptin and GLP-1 shape brain function.
Explore further
Search YouTube for…
Tap a phrase to copy it, then paste it into YouTube's search box. This site doesn't link to other websites — pick channels from universities, hospitals and established science educators.
Tagschemistryhormoneshypothalamusstress
Keep reading
Neurotransmitters & Brain Chemistry
Beginner
Dopamine
Not simply the 'pleasure chemical': dopamine drives movement, motivation and learning from surprises. Its pathways, the reward-prediction-error discovery, and its role in Parkinson's disease, addiction and schizophrenia.
January 19, 2026 · 3 min read
Neurotransmitters & Brain Chemistry
Intermediate
Acetylcholine
The first neurotransmitter ever identified: it moves every skeletal muscle, slows the heart, sharpens attention and memory — and is the target of curare, nerve agents, Alzheimer's drugs and myasthenia gravis.
December 21, 2025 · 2 min read
Neurotransmitters & Brain Chemistry
Intermediate
Noradrenaline and Adrenaline
The fight-or-flight chemicals: noradrenaline from the locus coeruleus tunes alertness and attention in the brain, while adrenaline from the adrenal glands readies the body for action.
December 6, 2025 · 2 min read