The pituitary gland secretes at least eight major hormones that control growth, metabolism, reproduction, stress responses, and water balance. Despite being only about the size of a pea, this gland at the base of your brain acts as a central command hub, sending chemical signals to organs and glands throughout the body. Its two main lobes, the anterior and posterior, each handle different hormones and operate through different mechanisms.
Anterior Lobe: Six Hormones That Drive Major Body Systems
The front portion of the pituitary, called the anterior lobe, manufactures and releases six hormones. Each one targets a specific organ or tissue, and together they regulate everything from how tall a child grows to whether a person can reproduce.
Growth hormone (GH) does exactly what its name suggests in children: it drives bone and tissue growth. In adults, it shifts roles, helping maintain muscle mass, bone density, and healthy body fat distribution. Growth hormone follows a strong daily rhythm. The largest pulses occur during deep sleep at night, with smaller bursts happening roughly every three to three and a half hours during the day. Fasting also triggers higher growth hormone output, which signals the body to burn stored fat and release glucose from the liver.
Thyroid-stimulating hormone (TSH) tells your thyroid gland to produce the hormones that set your metabolic rate. When thyroid hormone levels drop, the pituitary releases more TSH to compensate. When levels are sufficient, TSH production slows down.
Adrenocorticotropic hormone (ACTH) targets the adrenal glands, which sit on top of your kidneys. It triggers them to release cortisol and other stress-related hormones that regulate metabolism and immune function.
Luteinizing hormone (LH) and follicle-stimulating hormone (FSH) work as a pair to control reproduction. In males, LH stimulates testosterone production, while FSH supports sperm development. In females, FSH drives the maturation of egg-containing follicles in the ovaries, and a large burst of LH (called the LH surge) triggers ovulation. After ovulation, the remaining follicle cells form a structure that produces progesterone, which is essential for maintaining pregnancy.
Prolactin is best known for stimulating breast milk production after childbirth, but it also influences menstrual cycles, fertility, and sexual function in both sexes.
Posterior Lobe: Two Hormones It Stores but Doesn’t Make
The posterior lobe works differently from the anterior. It doesn’t actually produce any hormones. Instead, the hypothalamus (a small region just above the pituitary) manufactures two hormones and sends them down through a connecting stalk for storage. When the body needs them, nerve signals from the hypothalamus tell the posterior lobe to release them into the bloodstream.
Antidiuretic hormone (ADH), also called vasopressin, controls how much water your kidneys reabsorb. When you’re dehydrated, ADH levels rise, causing the kidneys to hold onto water and produce more concentrated urine. When you’re well-hydrated, ADH drops, and your kidneys let more water pass through.
Oxytocin triggers uterine contractions during labor and the release of breast milk during nursing. It also plays a broader role in social bonding, trust, and emotional connection, which is why it’s sometimes called the “bonding hormone.”
Melanocyte-Stimulating Hormone
The pituitary also produces melanocyte-stimulating hormone (MSH), which comes from the same precursor molecule as ACTH. MSH stimulates pigment-producing cells in the skin, and its production increases with exposure to ultraviolet light. Beyond skin pigmentation, MSH has a surprisingly wide reach: it can suppress appetite through receptors in the brain, reduce inflammation, influence the release of a hormone that controls salt and water balance, and affect sexual behavior.
How the Hypothalamus Controls Pituitary Output
The pituitary doesn’t decide on its own when to release hormones. The hypothalamus sends specific releasing or inhibiting signals that switch each hormone on or off. For example, corticotropin-releasing hormone from the hypothalamus tells the pituitary to produce ACTH, thyrotropin-releasing hormone triggers TSH release, and gonadotropin-releasing hormone prompts the release of both LH and FSH.
Some hypothalamic signals work as brakes rather than accelerators. Dopamine continuously suppresses prolactin release, so prolactin levels only rise significantly when that dopamine signal weakens (as happens after childbirth). Somatostatin blocks the secretion of growth hormone, TSH, and several other hormones, keeping them within their normal range.
Feedback Loops That Keep Hormones in Balance
The system runs on negative feedback, similar to a thermostat. When cortisol rises in response to ACTH, the elevated cortisol signals the hypothalamus to stop producing its releasing hormone, which in turn reduces ACTH output. The same principle applies to thyroid hormones: when levels are adequate, the hypothalamus and pituitary dial back TSH. This self-correcting loop prevents hormone levels from climbing too high or dropping too low under normal conditions.
When feedback loops malfunction, the consequences are significant. A pituitary tumor that overproduces prolactin (called a prolactinoma) can disrupt the reproductive system in both sexes. In females, this may cause irregular or absent periods, milky breast discharge outside of pregnancy, vaginal dryness, and difficulty getting pregnant. In males, excess prolactin can lead to erectile dysfunction, reduced body hair, smaller muscles, and breast tissue enlargement. In anyone, it can cause bone loss, reduced sex drive, and infertility. Large tumors can also press on nearby structures, causing headaches and vision problems.
Overproduction of growth hormone in adults leads to acromegaly, a condition where bones in the hands, feet, and face gradually thicken. In children, excess growth hormone causes abnormally rapid growth. Underproduction of any pituitary hormone creates the opposite problem: too little thyroid stimulation slows metabolism, too little ACTH leaves the body unable to mount a proper stress response, and too little growth hormone in children stunts their development.
How Pituitary Hormones Are Measured
Doctors check pituitary function through simple blood tests. Normal TSH levels fall between 0.5 and 4.0 mU/L, and values outside that range are often the first sign of a thyroid problem. ACTH normally ranges from 10 to 60 pg/mL, and growth hormone at rest sits below 5 ng/mL (it should rise above 7 ng/mL when the body is specifically challenged to produce it). Because growth hormone is released in pulses rather than at a steady rate, a single blood draw can miss a peak entirely, so doctors sometimes use stimulation tests to get an accurate reading.