Overview

Testosterone is known as the male hormone responsible for the development of male features like facial hair and a deeper voice than women. However, it is also thought to influence motivation and libido in both sexes.

In this article, you will find out how testosterone may impact libido in men and whether low levels of this hormone play a role.

What is testosterone?

Testosterone is a sex hormone produced in the testicles of men and the ovaries and adrenal glands in women. Testosterone belongs to a group of hormones called androgens,  hormones that promote the development and maintenance of male sex characteristics ¹.

Testosterone is considered the main sex hormone in the bodies of males assigned at birth due to its key role in the development of the male genitalia during pregnancy. Moreover, testosterone has earned this title due to its higher production and levels compared to the female body.¹

Leydig cells in the testicles start producing testosterone early in life to support the normal formation of the male urogenital tract. Later, during puberty, testosterone production increases dramatically and supports the male body's primary maturation, which impacts:¹

• The growth of the penis and testicles
• Sperm production (spermatogenesis)
• Fertility
• Libido

During those first years, testosterone also contributes to the development of the secondary sexual features of the male body, such as:¹

• Body hair
• Facial hair
• Male hair pattern
• Larger and more muscular bodies than women
• Voice deepening

Testosterone is also thought to influence:²

• Mood
• Energy
• Behavior (e.g., courtship efforts)

Normal testosterone levels by age

The production of testosterone changes over time. During puberty, the male body dramatically increases testosterone production and maintains this rhythm during adolescence, reaching its maximum around the age of 17 to 19. Testosterone levels remain high during adulthood but start dropping very gradually after the age of 30. After this age, production drops over time by about 100 ng/dL every 10 years.^1,3

Young adults typically have testosterone blood levels between 600 and 900 ng/dL. In contrast, older men fall between 500 and 800 ng/dL.³

With age, about 40% of men older than 45 and 50% of men in their 80s could repetitively test low for testosterone and, thereby, be classified as hypogonadal.³

Understanding low libido in men

Experts define libido as “sexual desire or the mental energy or emotion related to sex” .⁴

People usually describe libido as a cognitive or mental occurrence that is directly connected to arousal. It is thought to be the result of a complex interplay between physical, psychological, and social factors. Gender/sex and sexual orientation/identity may also play a role.^{5, 6}

A person may report low libido when they experience a reduced interest in sexual activity, suddenly or over time. Experts consider a decline in libido a natural part of the aging process, and it may not be absolute. Some older men still have some degree of sexual desire well into their 60s and 70s.⁷

The role of testosterone in libido

Testosterone is thought to be responsible for many aspects of human behavior, including libido. In fact, testosterone may be the differentiating factor between men and women in terms of libido. 

Sexual desire, libido, or sexual drive originates in the brain; therefore, the role of testosterone in libido takes place there. The human brain has androgen receptors in multiple brain regions involved in sexual response and behavior, including ⁸:

• Hypothalamus
• Amygdala
• Midbrain
• Frontal and prefrontal areas 
• Cingulate gyrus

Libido is then thought to fuel the body's sexual reactions: arousal and erection. In the latter case, testosterone initiates the production of nitric oxide. The resulting relaxation of the smooth muscle of the penile tissue leads to its erection ⁸.

How low testosterone affects libido

Despite the apparent determining role of testosterone in men's libido, the science behind this link is far from simple.

Studies in healthy young men have reported a weak or null association between testosterone levels and self-reported libido, measured as masturbation frequency.^{9, 10}

In contrast, for men in their 40s and older, higher testosterone levels may more clearly correlate with greater libido, along with better erectile function and higher sexual activity. This is also true for men with sexual dysfunction.^{11, 12, 13, 14, 15}

Moreover, in studies of hypogonadal men and men suffering from sexual dysfunction, those who underwent testosterone replacement therapy (TRT) found improvement in their symptoms, which included low sexual desire.^{16, 17, 18}

Additional research is needed to clarify which of the three forms in which testosterone circulates in blood is more tightly linked to libido. Earlier studies found that declining levels of bioavailable testosterone may be more linked to lower libido than total testosterone levels.¹⁹

Other causes of low libido in men

Besides testosterone levels, many other factors have been linked to low libido in men. For example, obesity is known to be detrimental to sexual desire due to its negative impact on testosterone levels. In line with this, weight loss strategies, for example dietary changes and exercise have been shown to increase both testosterone levels and libido.²⁰ 

Body fat reduction may help by decreasing aromatase, which is a fatty tissue enzyme that converts testosterone into estrogen. Moreover, weight loss may support testosterone production by lowering inflammation and improving insulin sensitivit.^{20, 21}

Strenuous exercise may also reduce sexual drive, as seen in marathon runners. High physical demand may put these athletes under increased fatigue, insufficient energy intake, or hormonal adaptations that cause a reduction in resource targeting for sexual activity.^{22, 23}

Other factors linked to low libido include:^{3, 8, 14, 24, 25, 26, 27, 28}

• Other hormone levels (e.g., estrogen, prolactin, thyroid hormones)
• Current cigarette smoking
• Frequent nocturnal urination
• Stress
• Chronic health conditions (e.g., diabetes, HIV) 
• Age

Some drugs may reduce testosterone levels, and, potentially, your libido may also take a hit. Examples include medication for:²⁹

• High cholesterol (e.g., statins)
• Fungi or yeast infections (e.g., ketoconazole)
• Depression

When to test testosterone levels

Low libido may stem from a variety of circumstances beyond abnormal testosterone levels. However, its coexistence with some of the following symptoms may require testosterone testing:³⁰

• Erectile dysfunction
• Decreased frequency of morning erections
• Fatigue
• Increased visceral body fat/obesity
• Decreased lean muscle mass
• Decreased strength
• Flushes
• Loss of facial, axillary, and pubic hair/slow beard growth
• Decline in the general feeling of well-being
• Depressed mood, mood changes, irritability
• Sleep disturbances

Discuss your symptoms with your doctor, especially if your libido drops suddenly. Remember that for reliable results, you may need to get your testosterone measured in the morning, which is when it is at its peak.⁷

The normal range for morning testosterone in men varies by laboratory, but it is generally between 300 ng/dL and 1000 ng/dL.³

When to see a doctor

• Persistent or sudden low libido
• Sexual difficulties
• Signs of hormonal imbalance: fatigue, loss of body hair, reduced muscle mass, flushes

FAQs

Does low testosterone cause low libido in men?

Yes, low testosterone is a cause of decreased libido in men. Testosterone plays a key role in regulating sex drive, and low levels could lead to reduced interest in sexual activity.

What are the symptoms of low testosterone besides low libido?

Other symptoms include fatigue, mood changes, loss of muscle mass and body hair, increased body fat, and erectile dysfunction.

Summary

• Low testosterone is one but not the only cause of low libido in men
• Testing and proper diagnosis, especially when the drop in libido is sudden, are key before considering treatment
• Talk to your doctor about your symptoms to find the right solution for you