Prolactin and testosterone are two powerful endocrine hormones that exert widespread influence over human physiology. While testosterone is widely recognized for its role in reproduction and male characteristics, prolactin is primarily known for its function in milk production. The relationship between these two hormones is not one of simple coexistence; rather, it is a delicate balance where an excess of prolactin can directly interfere with and suppress the body’s ability to produce testosterone. This negative interaction can lead to a condition known as hypogonadism, which results in significant health implications for both men and women.
The Normal Roles of Both Hormones
Prolactin is a hormone produced by the pituitary gland at the base of the brain. It is responsible for stimulating the growth of mammary tissue and initiating lactation following childbirth, and also contributes to metabolism and immune system regulation. For males and non-pregnant females, prolactin levels are typically low, averaging around 5 ng/mL in men and under 25 ng/mL in women who are not pregnant or nursing.
Testosterone is the primary androgen produced mainly in the testes in men and in smaller quantities by the ovaries and adrenal glands in women. In males, it drives the development of secondary sexual characteristics, promotes muscle mass, and regulates sex drive and sperm production. In both sexes, testosterone supports bone density, contributes to energy levels, mood, and cognitive function. The normal adult male range spans from about 300 to 1,000 ng/dL.
How Prolactin Suppresses Testosterone Production
The mechanism by which elevated prolactin, called hyperprolactinemia, suppresses testosterone is rooted in the disruption of the Hypothalamic-Pituitary-Gonadal (HPG) axis, which controls reproductive hormone production. The process begins in the hypothalamus, a region of the brain that secretes Gonadotropin-Releasing Hormone (GnRH) in a pulsatile manner.
High levels of prolactin inhibit the release of GnRH from the hypothalamus, causing a breakdown in the signal sent to the pituitary gland. Consequently, the pituitary gland is unable to release adequate amounts of the gonadotropins, Luteinizing Hormone (LH) and Follicle-Stimulating Hormone (FSH).
Luteinizing Hormone is the direct signal that instructs the Leydig cells in the testes to synthesize testosterone. With the LH signal diminished due to prolactin’s interference, the testes reduce their testosterone production, resulting in low serum testosterone levels. This state of hormonal deficiency is medically classified as hypogonadotropic hypogonadism.
Common Causes of Prolactin Elevation
Prolactin levels can become abnormally high for various reasons. The most common pathological cause is a prolactinoma, a benign tumor of the pituitary gland that overproduces prolactin. Other pathological conditions, such as an underactive thyroid (hypothyroidism) or chronic kidney and liver diseases, can also lead to elevated prolactin levels.
Certain medications are a pharmacological cause of prolactin elevation. Drugs that interfere with dopamine signaling—the brain’s main mechanism for inhibiting prolactin release—can cause hyperprolactinemia. This includes some antipsychotic medications, certain antidepressants, and specific drugs used to treat nausea or acid reflux.
Physiological causes are typically transient and include intense physical or emotional stress, strenuous exercise, and even sleep. Additionally, conditions that cause chronic irritation or trauma to the chest wall, such as shingles or surgery, can trigger a reflex increase in prolactin secretion.
Health Consequences of the Imbalance
The resulting low testosterone state from hyperprolactinemia causes symptoms affecting sexual, physical, and mental well-being. One immediate consequence is sexual dysfunction, including a reduced libido and, in men, erectile dysfunction. The hormonal imbalance also impairs fertility, as the diminished LH and FSH levels lead to reduced sperm production in men.
Beyond sexual health, the imbalance affects body composition and physical strength. Individuals frequently experience a decrease in lean muscle mass and an increase in overall body fat. Men may also develop gynecomastia, which is the enlargement of breast tissue.
Prolonged low testosterone leads to a reduction in bone mineral density. This loss of density, known as osteopenia or osteoporosis, increases the risk of bone fractures. These physical symptoms are often accompanied by psychological effects, such as persistent fatigue and mood disturbances.