Several studies have shown that hypopituitarism is associated with an increased risk of cardiovascular disease and some also an increased risk of death of about 50% to 150% the normal population. It has been difficult to establish which hormone deficiency is responsible for this risk, as almost all patients studied had growth hormone deficiency. The studies also do not answer the question as to whether the hypopituitarism itself causes the increased mortality, or whether some of the risk is to be attributed to the treatments, some of which (such as sex hormone supplementation) have a recognized adverse effect on cardiovascular risk.

The largest study to date followed over a thousand people for eight years; it showed an 87% increased risk of death compared to the normal population. Predictors of higher risk were: female sex, absence of treatment for sex hormone deficiency, younger age at the time of diagnosis, and a diagnosis of craniopharyngioma. Apart from cardiovascular disease, this study also showed an increased risk of death from lung disease.

Quality of life may be significantly reduced, even in those people on optimum medical therapy. Many report both physical and psychological problems. It is likely that the commonly used replacement therapies do not completely mimic the natural hormone levels in the body. Health costs remain about double those of the normal population.

Hypopituitarism is usually permanent. It requires lifelong treatment with one or more medicines.

Thyroid hormone resistance syndrome is rare, incidence is variously quoted as 1 in 50,000 or 1 in 40,000 live births. More than 1000 individuals have been identified with thyroid hormone resistance, of which 85% had thyroid hormone beta receptor mutation.

Autopsy studies indicate that 6-25% of the U. S. population have small pituitary tumors. Forty percent of these pituitary tumors produce prolactin, but most are not considered clinically significant. Clinically significant pituitary tumors affect the health of approximately 14 out of 100,000 people. In non-selective surgical series, this tumor accounts for approximately 25-30% of all pituitary adenomas. Some growth hormone (GH)–producing tumors also co-secrete prolactin. Microprolactinomas are much more common than macroprolactinomas.

The cause of pituitary tumors remains unknown. It has been shown that stress can significantly raise prolactin levels, which should make stress a diagnostic differential, though it usually is not considered such. Most pituitary tumors are sporadic — they are not genetically passed from parents to offspring.

The majority of moderately raised prolactin levels (up to 5000 mIU/L) are not due to microprolactinomas but other causes. The effects of some prescription drugs are the most common. Other causes are other pituitary tumours and normal pregnancy and breastfeeding. This is discussed more under hyperprolactinaemia.

The xenoestrogenic chemical Bisphenol-A has been shown to lead to hyperprolactinaemia and growth of prolactin-producing pituitary cells. The increasing and prolonged exposure of Bisphenol-A from childhood on, may contribute to the growth of a Prolactinoma.

Carcinomas that metastasize into the pituitary gland are uncommon and typically seen in the elderly, with lung and breast cancers being the most prevalent, In breast cancer patients, metastases to the pituitary gland occur in approximately 6-8% of cases.

Symptomatic pituitary metastases account for only 7% of reported cases. In those who are symptomatic Diabetes insipidus often occurs with rates approximately 29-71%. Other commonly reported symptoms include anterior pituitary dysfunction, visual field defects, headache/pain, and ophthalmoplegia.

There is only one study that has measured the prevalence (total number of cases in a population) and incidence (annual number of new cases) of hypopituitarism. This study was conducted in Northern Spain and used hospital records in a well-defined population. The study showed that 45.5 people out of 100,000 had been diagnosed with hypopituitarism, with 4.2 new cases per year. 61% were due to tumors of the pituitary gland, 9% due to other types of lesions, and 19% due to other causes; in 11% no cause could be identified.

Recent studies have shown that people with a previous traumatic brain injury, spontaneous subarachnoid hemorrhage (a type of stroke) or radiation therapy involving the head have a higher risk of hypopituitarism. After traumatic brain injury, as much as a quarter have persistent pituitary hormone deficiencies. Many of these people may have subtle or non-specific symptoms that are not linked to pituitary problems but attributed to their previous condition. It is therefore possible that many cases of hypopituitarism remain undiagnosed, and that the annual incidence would rise to 31 per 100,000 annually if people from these risk groups were to be tested.

Certain medications can have the unintended side effect of affecting thyroid function. While some medications can lead to significant hypothyroidism or hyperthyroidism and those at risk will need to be carefully monitored, some medications may affect thyroid hormone lab tests without causing any symptoms or clinical changes, and may not require treatment. The following medications have been linked to various forms of thyroid disease:

- Amiodarone (more commonly can lead to hypothyroidism, but can be associated with some types of hyperthyroidism)

- Lithium salts (hypothyroidism)

- Some types of interferon and IL-2 (thyroiditis)

- Glucocorticoids, dopamine agonists, and somatostatin analogs (block TSH, which can lead to hypothyroidism)

Iatrogenic Cushing's syndrome (caused by treatment with corticosteroids) is the most common form of Cushing's syndrome. Cushing's disease is rare; a Danish study found an incidence of less than one case per million people per year. However, asymptomatic microadenomas (less than 10 mm in size) of the pituitary are found in about one in six individuals.

People with Cushing's syndrome have increased morbidity and mortality as compared to the general population. The most common cause of mortality in Cushing's syndrome is cardiovascular events. People with Cushing's syndrome have nearly 4 times increased cardiovascular mortality as compared to the general population.

Hyperthyroidism is a state in which the body is producing too much thyroid hormone. The main hyperthyroid conditions are:

- Graves' disease

- Toxic thyroid nodule

- Thyroid storm

- Toxic nodular struma (Plummer's disease)

- Hashitoxicosis: "transient" hyperthyroidism that can occur in Hashimoto's thyroiditis

Adenomas of the anterior pituitary gland are a major clinical feature of multiple endocrine neoplasia type 1 (MEN1), a rare inherited endocrine syndrome that affects 1 person in every 30,000. MEN causes various combinations of benign or malignant tumors in various glands in the endocrine system or may cause the glands to become enlarged without forming tumors. It often affects the parathyroid glands, pancreatic islet cells, and anterior lobe of the pituitary gland. MEN1 may also cause non-endocrine tumors such as facial angiofibromas, collagenomas, lipomas, meningiomas, ependymomas, and leiomyomas. Approximately 25 percent of patients with MEN1 develop pituitary adenomas.

Outcomes are typically good when treated. Most can expect to live relatively normal lives. Someone with the disease should be observant of symptoms of an "Addison's crisis" while the body is strained, as in rigorous exercise or being sick, the latter often needing emergency treatment with intravenous injections to treat the crisis.

Individuals with Addison's disease have more than a doubled mortality rate. Furthermore, individuals with Addison's disease and diabetes mellitus have an almost 4 time increase in mortality compared to individuals with only diabetes.

The most common cause of Cushing's syndrome is the taking of glucocorticoids prescribed by a health care practitioner to treat other diseases (called iatrogenic Cushing's syndrome). This can be an effect of corticosteroid treatment of a variety of disorders such as asthma and rheumatoid arthritis, or in immunosuppression after an organ transplant. Administration of synthetic ACTH is also possible, but ACTH is less often prescribed due to cost and lesser utility. Although rare, Cushing's syndrome can also be due to the use of medroxyprogesterone acetate. In this form of Cushing's, the adrenal glands atrophy due to lack of stimulation by ACTH, since glucocorticoids downregulate production of ACTH. Cushing's syndrome in childhood usually results from use of glucocorticoid medication.

Endogenous Cushing's syndrome results from some derangement of the body's own system of secreting cortisol. Normally, ACTH is released from the pituitary gland when necessary to stimulate the release of cortisol from the adrenal glands.

- In pituitary Cushing's, a benign pituitary adenoma secretes ACTH. This is also known as Cushing's disease and is responsible for 70% of endogenous Cushing's syndrome.

- In adrenal Cushing's, excess cortisol is produced by adrenal gland tumors, hyperplastic adrenal glands, or adrenal glands with nodular adrenal hyperplasia.

- Tumors outside the normal pituitary-adrenal system can produce ACTH (occasionally with CRH) that affects the adrenal glands. This etiology is called ectopic or paraneoplastic Cushing's disease and is seen in diseases such as small cell lung cancer.

- Finally, rare cases of CRH-secreting tumors (without ACTH secretion) have been reported, which stimulates pituitary ACTH production.

All causes in this category are genetic, and generally very rare. These include mutations to the "SF1" transcription factor, congenital adrenal hypoplasia due to "DAX-1" gene mutations and mutations to the ACTH receptor gene (or related genes, such as in the Triple A or Allgrove syndrome). "DAX-1" mutations may cluster in a syndrome with glycerol kinase deficiency with a number of other symptoms when "DAX-1" is deleted together with a number of other genes.

The frequency rate of Addison's disease in the human population is sometimes estimated at roughly one in 100,000. Some put the number closer to 40–144 cases per million population (1/25,000–1/7,000). Addison's can affect persons of any age, sex, or ethnicity, but it typically presents in adults between 30 and 50 years of age. Research has shown no significant predispositions based on ethnicity.

Pseudoacromegaly is a condition with the usual acromegaloid features, but without an increase in growth hormone and IGF-1. It is frequently associated with insulin resistance. Cases have been reported due to minoxidil at an unusually high dose. It can also be caused by a selective postreceptor defect of insulin signalling, leading to the impairment of metabolic, but preservation of mitogenic, signalling.

Almost all cases of pituitary apoplexy arise from a pituitary adenoma, a benign tumor of the pituitary gland. In 80%, the patient has been previously unaware of this (although some will retrospectively report associated symptoms). It was previously thought that particular types of pituitary tumors were more prone to apoplexy than others, but this has not been confirmed. In absolute terms, only a very small proportion of pituitary tumors eventually undergoes apoplexy. In an analysis of incidentally found pituitary tumors, apoplexy occurred in 0.2% annually, but the risk was higher in tumors larger than 10 mm ("macroadenomas") and tumors that were growing more rapidly; in a meta-analysis, not all these associations achieved statistical significance.

The majority of cases (60–80%) are not precipitated by a particular cause. A quarter has a history of high blood pressure, but this is a common problem in the general population, and it is not clear whether it significantly increase the risk of apoplexy. A number of cases has been reported in association with particular conditions and situations; it is uncertain whether these were in fact causative. Amongst reported associations are surgery (especially coronary artery bypass graft, where there are significant fluctuations in the blood pressure), disturbances in blood coagulation or medication that inhibits coagulation, radiation therapy to the pituitary, traumatic brain injury, pregnancy (during which the pituitary enlarges) and treatment with estrogens. Hormonal stimulation tests of the pituitary have been reported to provoke episodes. Treatment of prolactinomas (pituitary adenomas that secrete prolactin) with dopamine agonist drugs, as well as withdrawal of such treatment, has been reported to precipitate apoplexy.

Hemorrhage from a Rathke's cleft cyst, a remnant of Rathke's pouch that normally regresses after embryological development, may cause symptoms that are indistinguishable from pituitary apoplexy. Pituitary apoplexy is regarded by some as distinct from Sheehan's syndrome, where the pituitary undergoes infarction as a result of prolonged very low blood pressure, particularly when caused by bleeding after childbirth. This condition usually occurs in the absence of a tumor. Others regard Sheehan's syndrome as a form of pituitary apoplexy.

In larger case series, the mortality was 1.6% overall. In the group of patients who were unwell enough to require surgery, the mortality was 1.9%, with no deaths in those who could be treated conservatively.

After an episode of pituitary apoplexy, 80% of people develop hypopituitarism and require some form of hormone replacement therapy. The most common problem is growth hormone deficiency, which is often left untreated but may cause decreased muscle mass and strength, obesity and fatigue. 60–80% require hydrocortisone replacement (either permanently or when unwell), 50–60% need thyroid hormone replacement, and 60–80% of men require testosterone supplements. Finally, 10–25% develop diabetes insipidus, the inability to retain fluid in the kidneys due to a lack of the pituitary antidiuretic hormone. This may be treated with the drug desmopressin, which can be applied as a nose spray or taken by mouth.

A pituitary disease is a disorder primarily affecting the pituitary gland.

The main disorders involving the pituitary gland are:

Overproduction or underproduction of a pituitary hormone will affect the respective end-organ. For example, insufficient production (hyposecretion) of thyroid stimulating hormone (TSH) in the pituitary gland will cause hypothyroidism, while overproduction (hypersecretion) of TSH will cause hyperthyroidism. Thyroidisms caused by the pituitary gland are less common though, accounting for less than 10% of all hypothyroidism cases and much less than 1% of hyperthyroidism cases.

Autoimmune adrenalitis is the most common cause of Addison's disease in the industrialised world. Autoimmune destruction of the adrenal cortex is caused by an immune reaction against the enzyme 21-hydroxylase (a phenomenon first described in 1992). This may be isolated or in the context of autoimmune polyendocrine syndrome (APS type 1 or 2), in which other hormone-producing organs, such as the thyroid and pancreas, may also be affected.

Adrenal destruction is also a feature of adrenoleukodystrophy (ALD), and when the adrenal glands are involved in metastasis (seeding of cancer cells from elsewhere in the body, especially lung), hemorrhage (e.g. in Waterhouse-Friderichsen syndrome or antiphospholipid syndrome), particular infections (tuberculosis, histoplasmosis, coccidioidomycosis), or the deposition of abnormal protein in amyloidosis.

Normal thyroid hormone function requires normal thyroid hormone transport across cell membrane, appropriate deiodination, thyroid hormone nuclear receptor, thyroid hormone response elements, co-activators, co-repressors, and normal histone acetylation. Any abnormalities in this chain can result in thyroid hormone resistance.

The most common cause of the syndrome are mutations of the β (beta) form ("THRB" gene) of the thyroid hormone receptor, of which over 100 different mutations have been documented.

Mutations in "MCT8" and "SECISBP2" have also been associated with this condition.

Sequence of events:

1. Iodine deficiency leading to decreased T4 production.

2. Induction of thyroid cell hyperplasia due to low levels of T4. This accounts for the multinodular goitre appearance.

3. Increased replication predisposes to a risk of mutation in the TSH receptor.

4. If the mutated TSH receptor is constitutively active, it would then become 'toxic' and produces excess T3/T4 leading to hyperthyroidism.

Radiation therapy has been used both as a primary treatment and combined with surgery or drugs. It is usually reserved for patients who have tumor remaining after surgery. These patients often also receive medication to lower GH levels. Radiation therapy is given in divided doses over four to six weeks. This treatment lowers GH levels by about 50 percent over 2 to 5 years. Patients monitored for more than 5 years show significant further improvement. Radiation therapy causes a gradual loss of production of other pituitary hormones with time. Loss of vision and brain injury, which have been reported, are very rare complications of radiation treatments.

Women being treated for Hashimoto's disease can become pregnant. It is recommended that thyroid function be well-controlled before getting pregnant.

Untreated or poorly treated underactive thyroid can lead to problems for the mother, such as:

- Preeclampsia

- Anemia

- Miscarriage

- Placental abruption

- High cholesterol

- Postpartum bleeding

It also can cause serious problems for the baby, such as:

- Preterm birth

- Low birth weight

- Stillbirth

- Birth defects

- Thyroid problems

Growth hormone-releasing hormone (GHRH) is another releasing factor secreted by the hypothalamus. GHRH stimulates the pituitary gland to secrete growth hormone (GH), which has various effects on body growth and sexual development. Insufficient GH production may cause poor somatic growth, precocious puberty or gonadotropin deficiency, failure to initiate or complete puberty, and is often associated with rapid weight gain, low T, and low levels of sex hormones.

An endocrine gland neoplasm is a neoplasm affecting one or more glands of the endocrine system.

Examples include:

- Adrenal tumor

- Pituitary adenoma

The most common form is thyroid cancer.

Condition such as pancreatic cancer or ovarian cancer can be considered endocrine tumors, or classified under other systems.

Pinealoma is often grouped with brain tumors because of its location.