All You Need to Know About Low Testosterone

Low testosterone can cause decreased sex drive, erectile dysfunction, hair loss, and more. The hormone testosterone is essential for male physical development and sperm creation. Among other things, it stimulates the production of red blood cells, plays a vital role in the development of the testis and prostate, promotes the growth of body hair, and sustains body mass.

Most testosterone is produced by the testes, but the levels are regulated by a feedback loop between the hypothalamus and pituitary gland. Thus, anything that impacts the testes, hypothalamus, or pituitary gland has the potential to cause low testosterone or "hypogonadism," which can cause sexual dysfunction and physical changes.

The feedback loop works as follows: When a man is aroused or when his testosterone levels are low, his hypothalamus (located just above the brain stem) stimulates testosterone production by sending gonadotropin-releasing hormones (GnRH) to the pituitary gland. The gland is responsible for creating a range of hormones that manage growth, blood pressure, thyroid function, and a host of other bodily functions. In particular, GnRH causes the pituitary to produce FSH (follicle-stimulating hormone) and LH (luteinizing hormone). When released into the bloodstream, these hormones travel to the testicles and trigger the testosterone production. If levels get too high, the pituitary gland will slow its release of these hormones. Conversely, if levels are too low, the gland can speed up their release.

Types of Low Testosterone

There are two types of low testosterone:

  • Primary hypogonadism is caused by a testicular malfunction (causes include tumor, infection, testicular injury, genetic defects, substance abuse, radiation therapy, or chemotherapy).

  • Secondary hypogonadism is when defects in the hypothalamus or the pituitary gland cause decreased testosterone production. Unlike primary hypogonadism, fertility can be renewed by stimulating the hormones through appropriate drug therapy.

Causes of Low Testosterone: Primary vs. Secondary

Primary low testosterone causes include:

  • Undescended testes at birth
  • Mumps, accompanied by inflammation of the testes
  • Testicular injury (either due to sports or surgery)
  • Tumors on the pituitary gland or testicles
  • Radiation or chemotherapy for testicular cancer
  • Genetic defects, such as Klinefelter Syndrome, a chromosomal condition that impacts male cognitive and physical development
  • Topical steroids placed on the scrotum due to certain conditions, such as jock rot or dermatitis
  • Viral infections, such as HIV/AIDS

Secondary low testosterone causes include:

  • Obesity
  • Hypertension
  • Type 2 diabetes
  • Genetic conditions, such as Kallmann syndrome, in which puberty is delayed or never comes
  • Some inflammatory diseases, such as tuberculosis or sarcoidosis, involve the pituitary gland and can affect testosterone levels
  • Viral infections, such as HIV/AIDS
  • Anabolic steroids used in bodybuilding and for sports enhancement

Other Causes of Low Testosterone

  • A diet high in animal products (hormones in livestock feed can act like estrogen once they're inside the human body)
  • Medications for depression, anxiety, high blood pressure, high cholesterol, and psychiatric illnesses
  • Substance abuse and alcohol consumption

Symptoms of Low Testosterone

The primary symptoms of low testosterone are resulting osteoporosis or low bone mass, tiredness, depression, poor sex drive, infertility, erectile dysfunction, and a reduction in strength and muscle mass.

Other symptoms include:

  • Delayed or unfinished sexual development
  • Fewer unprompted erections
  • Body-hair loss
  • Testicle shrinkage; minimal or nonexistent sperm count
  • Height reduction
  • Slight bone fractures

Diagnosis of Low Testosterone

A urologist can help diagnose low testosterone levels, which are often determined with a blood test, which should be taken around 8 a.m. when testosterone values are typically highest.

Additional tests used to diagnose hypogonadism include:

  • Semen analysis: This test, which measures the amount and quality of the sperm, is generally only conducted in men who have fertility issues.

  • Pituitary imaging: An MRI of the hypothalamic-pituitary area is appropriate if the laboratory analysis shows numerous abnormalities, including a low serum testosterone level. MRIs can also determine if there is a tumor in the area.

  • Testicular biopsy: A tissue sample is removed from the testicle and examined under a microscope to look for causes of infertility and for signs of infection, as well as to determine if the tissue is cancerous.

Treatment for Low Testosterone

When treating hypogonadism, or low testosterone, male hormone replacement therapy (MHRT) is the primary course of action. It can be administered in the form of gel, pellets, patches, oral inserts, and injections. You should discuss your treatment options for low testosterone with your physician or urologist.


Dr. Armon B. Neel Jr. (2012). 7 Meds that can wreck your sex life. AARP.

Pantalone KM, & Faiman C. (2012). Male hypogonadism: More than just a low testosterone. Cleveland Clinic Journal of Medicine.

Bhasin S, Cunningham GR, Hayes FJ, et al, (2010). Testosterone Therapy in Adult Men with Androgen Deficiency Syndromes: An Endocrine Society Clinical Practice Guideline. The Journal of Clinical Endocrinology and Metabolism.

Dandona P, & Rosenberg MT. (2010). A practical guide to male hypogonadism in the primary care setting. International Journal of Clinical Practice.

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