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Gynecomastia (American English) or gynaecomastia (British English) is the development of abnormally large breasts on men. The term comes from the Greek gyne meaning "woman" and mastos meaning "breast". The condition can occur physiologically in neonates, in adolescents, and in the elderly. In adolescent boys the condition is often a source of distress, but for the large majority of boys whose pubertal gynecomastia is not due to obesity, the breast development shrinks or disappears within a couple of years. The causes of common gynecomastia remain uncertain, although it has generally been attributed to an imbalance of sex hormones or the tissue responsiveness to them, A root cause is rarely determined for individual cases. Breast prominence can result from hypertrophy of either breast tissue or pectoral adipose tissue, and often a combination of the two. Breast prominence due solely to excessive adipose is often termed pseudogynecomastia.


Physiologic gynecomastia occurs in neonates, at puberty and with aging.

Potential pathologic causes of gynecomastia are: medications including hormones, increased serum estrogen, decreased testosterone production, androgen receptor defects, chronic kidney disease, chronic liver disease, HIV, and other chronic illness. Gynecomastia as a result of spinal cord injury and refeeding after starvation has been reported. In 25% of cases, the cause of the gynecomastia is not known.

Medications cause 10-20% of cases of gynecomastia in post-adolescent adults. These include cimetidine, omeprazole, spironolactone, finasteride and certain antipsychotics. Some act directly on the breast tissue, while others lead to increased secretion of prolactin from the pituitary by blocking the actions of dopamine (prolactin-inhibiting factor/PIF) on the lactotrope cell groups in the anterior pituitary. Androstenedione, used as a performance enhancing food supplement, can lead to breast enlargement by excess estrogen activity. Medications used in the treatment of prostate cancer, such as antiandrogens and GnRH analogs can also cause gynecomastia. Marijuana use is also thought by some to be a possible cause, but this is controversial.

Increased estrogen levels can also occur in certain testicular tumors, and in hyperthyroidism. Certain adrenal tumors cause elevated levels of androstenedione which is converted by the enzyme aromatase into estrone, a form of estrogen. Other tumors that secrete hCG can increase estrogen. A decrease in estrogen clearance can occur in liver disease, and this may be the mechanism of gynecomastia in liver cirrhosis. Obesity tends to increase estrogen levels.

Decreased testosterone production can occur in congenital or acquired testicular failure, for example in genetic disorders such as Klinefelter syndrome. Diseases of the hypothalamus or pituitary can also lead to low testosterone. Abuse of anabolic steroids has a similar effect.

Although stopping these medications can lead to regression of the gynecomastia, surgery is sometimes necessary to eliminate the condition.


The condition usually can be diagnosed by examination by a physician. Occasionally, imaging by X-rays or ultrasound is needed to confirm the diagnosis. Blood tests are required to see if there is any underlying disease causing the gynecomastia.


Gynecomastia is not physically harmful, but in some cases can be an indicator of other more dangerous underlying conditions. Furthermore, it can frequently present social and psychological difficulties for the sufferer. Weight loss can alter the condition in cases where it is triggered by obesity, but for many it will not eliminate it as the breast tissue remains.


Treating the underlying cause of the gynecomastia may lead to improvement in the condition. Patients should stop taking medications which can cause gynecomastia. Anti-estrogen medications, such as tamoxifen and clomiphene or androgens can be used. Aromatase inhibitors are another treatment option, although they are not universally approved for the treatment of gynecomastia. Endocrinological attention may help during the first 2-3 years. After that window, however, the breast tissue tends to remain and harden, leaving surgery (either liposuction or reduction mammoplasty) the only treatment option. Radiation therapy is sometimes used to prevent gynecomastia in patients with prostate cancer prior to estrogen therapy. There are people who choose to live with the condition and use a bra as an option for treatment.


  • Glass, AR (Dec 1994). "Gynecomastia". Endocrinol Metab Clin North Am 23 (4): 825-37. PMID 7705322.
  • Braunstein, GD (Jun 1999). "Aromatase and Gynecomastia". Endocr Relat Cancer 6 (2): 315-24. PMID 10731125.
  • Braunstein, GD (Feb 18 1993). "Gynecomastia". N Engl J Med 328 (7): 490-5. PMID 8421478.
  • Peyriere, H; et al (Oct 22 1999). "Report of gynecomastia in five male patients during antiretroviral therapy for HIV infection". AIDS 13 (15): 2167-9. PMID 10546872.
  • Heruti, RJ; et al (May 1997). "Gynecomastia following spinal cord disorder". Arch Phys Med Rehabil 78 (5): 534-7. PMID 9161376.

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