Gynecomastia is the term used to describe the enlargement of breasts in men or boys. True gynecomastia is defined by growth of actual breast tissue, not growth of fat tissue in the breast area. Imbalance of the sex hormones testosterone and estrogen is usually the immediate cause of gynecomastia. The hormonal imbalance may be caused by several different factors, including puberty or aging. However, 10 to 20 percent of gynecomastia cases are caused by prescription or illegal drugs, according to the University of Texas Health Science Center.
Anti-Androgens
Many drugs used to treat prostate cancer or enlarged prostate can increase the risk of gynecomastia. These anti-androgen medications block the action of testosterone and other male sex hormones, which tips the hormonal balance in favor of feminizing hormones, explains the University of California, Los Angeles Department of Medicine. Anti-androgen drugs include spironolactone, flutamide, cyproterone and finasteride.
Mood Altering Drugs
Gynecomastia can also be caused by certain types of medications that regulate moods. Tricyclic antidepressant drugs, the early antidepressants that have largely been replaced by selective serotonin reuptake inhibitors, and anti-anxiety drugs, including diazepam, which is commonly sold as Valium, have both been linked to gynecomastia. In addition, some antipsychotic medications, such as phenytoin, phenothiazines and haloperidol, also increase the growth of breast tissue in men.
AIDS Medications and Chemotherapy Drugs
Some men undergoing treatment for AIDS develop gynecomastia. Highly active antiretroviral therapy (HAART), which are highly aggressive treatment regimens that include combinations of different AIDS medicines, have been linked to abnormal breast tissue growth, particularly those including the drug efavirenz, according to the Mayo Clinic.com. In addition, many of the harsh chemicals used to treat cancer may also disrupt the sex hormone balance and cause gynecomastia. Certain ulcer medications, including cimetidine and omeprazole, may also induce gynecomastia. Certain antibiotic medications, including metronidazole and isoniazid increase the risk as well.
Heart Medications
Many of the commonly prescribed heart medications increase the risk of gynecomastia, including digitalis, also known as digoxin, amiodarone and certain calcium channel blocking drugs such as verapamil. ACE inhibitor drugs, which are used to treat high blood pressure, have also been known to cause gynecomastia.
Alcohol and Illegal Drugs
Heavy alcohol use is linked to gynecomastia, as are several illegal drugs including marijuana, heroin and amphetamines. Anabolic steroids that are used to enhance athletic performance also greatly increase the risk of unusual breast tissue growth. Anabolic steroids mimic the action of the male sex hormones. In the short term, this leads to an increase in masculine characteristics, including increased muscle and hair growth. However, in the long term, the delicate balance of hormones is disrupted, which can lead to the development of feminine characteristics such as breast growth, explains the National Institute on Drug Abuse.
