The pituitary gland produces six hormones and stores two others, giving it influence over growth, reproduction, metabolism, stress response, and water balance. Despite being only about the size of a pea, it sits at the base of your brain and acts as a relay between your brain and the rest of your endocrine system. This is why it’s often called the “master gland.”
How the Pituitary Takes Orders From the Brain
The pituitary doesn’t act on its own. A region of the brain called the hypothalamus sends chemical signals that tell the pituitary to ramp up or dial back each hormone. These signals travel through a dedicated network of tiny blood vessels that connect the hypothalamus directly to the front lobe of the pituitary. When hormone levels in the body get too high, feedback loops tell the hypothalamus to ease off, which in turn slows pituitary output. This back-and-forth keeps hormone levels within a tight range.
The gland has two distinct lobes, and they work differently. The front lobe (anterior pituitary) manufactures its own hormones. The back lobe (posterior pituitary) doesn’t make hormones at all. Instead, it stores and releases two hormones that the hypothalamus produces and ships down through nerve fibers.
The Six Hormones Made by the Front Lobe
Growth Hormone
Human growth hormone drives bone and muscle growth in children. In adults, it helps maintain muscle mass, bone density, and healthy body fat distribution. The pituitary releases it in pulses, mostly during deep sleep. Normal resting levels differ by sex: below 5 ng/mL in males and below 10 ng/mL in females. Newborns have much higher levels, ranging from 5 to 23 ng/mL, which gradually decline through the first year of life.
Thyroid-Stimulating Hormone (TSH)
TSH tells your thyroid gland to produce its hormones, which set the pace of your metabolism. When TSH is too high, the thyroid overworks and you can experience weight loss, a racing heart, and anxiety. When TSH is too low, the thyroid slows down, leading to fatigue, weight gain, and sluggish digestion. TSH is the single most important screening test for thyroid function because it reflects even small shifts before other thyroid markers change.
Adrenocorticotropic Hormone (ACTH)
ACTH targets the adrenal glands, which sit on top of your kidneys, and triggers them to release cortisol. Cortisol helps your body respond to stress, regulates blood sugar, controls inflammation, and influences blood pressure. ACTH follows a daily rhythm, peaking in the early morning and dropping at night. A healthy morning cortisol level generally falls above 15 micrograms per deciliter; levels below 3 at that time strongly suggest the pituitary isn’t producing enough ACTH.
Follicle-Stimulating Hormone (FSH)
FSH is central to reproduction. In women, it stimulates the ovaries to mature eggs each cycle. Between days 6 and 14 of a typical menstrual cycle, FSH causes follicles in one ovary to grow and prepare for ovulation. In men, FSH drives sperm production in the testes. FSH also plays a role before birth: during the second and third trimesters, a developing fetus’s own pituitary begins releasing FSH to help organize the reproductive system.
Luteinizing Hormone (LH)
LH works alongside FSH but has a distinct trigger role. In women, a sudden surge of LH around day 14 of the menstrual cycle causes the mature follicle to rupture and release an egg. This is the moment of ovulation that home ovulation kits detect. In men, LH stimulates the testes to produce testosterone, which then collaborates with FSH to sustain ongoing sperm production. During puberty, rising LH and FSH together are what kick-start testosterone production in boys and estrogen production in girls.
Prolactin
Prolactin is best known for triggering breast milk production after childbirth, but its roles extend well beyond lactation. It influences insulin sensitivity, lipid metabolism, and energy balance. It also acts on immune cells, contributing to both the body’s first-line defenses and its more targeted immune responses. In the brain, prolactin supports the growth and repair of nerve cells and promotes the formation of myelin, the insulating coating around nerves. Despite all these functions, prolactin deficiency in men and non-pregnant, non-lactating women doesn’t appear to cause significant health problems.
The Two Hormones Stored in the Back Lobe
Antidiuretic Hormone (ADH)
ADH, also called vasopressin, controls how much water your kidneys hold onto versus how much they let pass into urine. When you’re dehydrated, the hypothalamus ramps up ADH release so your kidneys reabsorb more water, concentrating your urine. When you’re well hydrated, ADH drops and you produce more dilute urine. A complete loss of ADH release leads to a condition where the body can’t concentrate urine at all, resulting in excessive thirst and urination.
Oxytocin
Oxytocin triggers uterine contractions during labor and causes breast milk to flow when a baby nurses. It also plays a role in parent-child bonding for both mothers and fathers. In men, oxytocin contributes to ejaculation by contracting the tubes that transport sperm. Beyond reproduction, oxytocin is widely associated with social bonding and trust, though its everyday effects in non-reproductive contexts are still being mapped out.
What Happens When the Pituitary Overproduces
Pituitary tumors are the most common cause of hormone overproduction. About 100 in every 100,000 people are living with a pituitary tumor that needs medical attention, and 4 to 7 new cases per 100,000 are diagnosed each year. Most are benign growths called adenomas, and their symptoms depend entirely on which hormone they’re pumping out.
A tumor producing excess ACTH causes Cushing disease: weight gain concentrated around the belly and upper back, a rounded face, thin skin that bruises easily, stretch marks, muscle weakness in the arms and legs, and slow wound healing. An excess of growth hormone in adults leads to acromegaly, which gradually enlarges the hands, feet, and facial features, thickens the skin, and can cause joint pain, sleep apnea, and high blood sugar.
Prolactin-secreting tumors (prolactinomas) are the most common type. In women, they cause irregular or missed periods, unexpected breast discharge, and fertility problems. In men, they lower testosterone, reduce sex drive, and can lead to breast tissue growth. TSH-producing tumors, though rare, push the thyroid into overdrive, causing weight loss, a rapid heartbeat, tremors, and anxiety.
What Happens When the Pituitary Underproduces
When the pituitary fails to make enough of one or more hormones, the condition is called hypopituitarism. It can result from tumors pressing on healthy tissue, surgery, radiation, head injuries, or autoimmune inflammation. The symptoms mirror whatever hormone is missing. Low TSH output leaves you hypothyroid. Low ACTH means your adrenals can’t make enough cortisol, which can cause fatigue, low blood pressure, and dangerous crashes during illness or injury. Low FSH and LH lead to fertility problems and, in men, low testosterone.
Diagnosis typically starts with blood tests measuring both the pituitary hormone and the hormone from its target gland. For example, if your thyroid hormone is low but TSH isn’t elevated in response, the problem points to the pituitary rather than the thyroid itself. Growth hormone deficiency is trickier to confirm because GH levels fluctuate throughout the day, so doctors often use stimulation tests that challenge the pituitary to produce a peak response. A peak below 3 ng/mL on those tests confirms deficiency.
Because the pituitary controls so many systems at once, a single pituitary problem can cascade into deficiencies across multiple hormones. When three or more hormonal axes are affected, the pattern itself becomes a diagnostic clue, and testing can sometimes be streamlined based on that broader picture.