Hypopituitarism: This condition, characterized by the underproduction of one or more pituitary hormones, is a common cause of low prolactin levels. The pituitary gland produces prolactin, and any damage or dysfunction to this gland can lead to decreased prolactin secretion.

Stress Reduction: Prolactin levels can decrease with reduced stress, as stress is a known stimulator of prolactin release.
Dopamine Excess: Dopamine inhibits prolactin release from the pituitary gland. Therefore, conditions or medications that increase dopamine levels can lead to low prolactin levels.
Certain Medications: Some medications, such as antipsychotics that block dopamine receptors, can initially increase prolactin levels but may lead to decreased levels upon long-term use due to pituitary gland downregulation.

Pituitary Apoplexy: Although rare, this condition involves sudden hemorrhage or infarction of the pituitary gland, which can lead to acute hypopituitarism, including low prolactin levels. It is a medical emergency.
Cranial Irradiation: Radiation therapy to the brain can damage the pituitary gland, leading to hypopituitarism and low prolactin levels. This is a critical diagnosis to consider in patients with a history of cranial irradiation.

Lymphocytic Hypophysitis: An autoimmune condition that causes inflammation of the pituitary gland, leading to hypopituitarism, including low prolactin levels.
Pituitary Tumors (Non-Prolactinoma): While prolactinomas (prolactin-secreting tumors) increase prolactin levels, other types of pituitary tumors can compress or destroy normal pituitary tissue, leading to low prolactin levels.
Genetic Disorders: Certain genetic conditions can affect pituitary development or function, leading to hypopituitarism and low prolactin levels. Examples include combined pituitary hormone deficiency (CPHD) and familial forms of hypopituitarism.