What Is Low Testosterone? Symptoms, Causes, and What to Do

Men's Lifestyle, Testosterone Therapy

Testosterone is the hormone most men associate with vitality, strength, and drive. When levels drop below a healthy range, the effects are rarely dramatic at first. They tend to be gradual: energy fades, mood shifts, body composition changes. Many men spend years attributing these changes to stress or aging without realizing the underlying cause may be measurable, and addressable. This article covers what low testosterone actually is, what causes it, how to recognize it, and what steps to consider if you think it applies to you.

What Is Low Testosterone?

Testosterone is the primary male sex hormone, produced mainly in the testes under direction from the brain via a signaling chain called the hypothalamic-pituitary-gonadal (HPG) axis. The hypothalamus releases gonadotropin-releasing hormone (GnRH), which signals the pituitary gland to release luteinizing hormone (LH) and follicle-stimulating hormone (FSH). LH then triggers testosterone production in Leydig cells within the testes ( 1 ).

Low testosterone, clinically referred to as hypogonadism or testosterone deficiency syndrome, is diagnosed when blood testosterone levels fall below a threshold that the body needs to function normally. The American Urological Association defines low testosterone as a total serum testosterone level below 300 ng/dL, though symptoms and context matter as much as the number ( 2 ). A man with levels at 290 ng/dL who feels fine may need less intervention than one at 320 ng/dL who is experiencing significant symptoms.

There are two main categories: primary hypogonadism (a problem with the testes themselves) and secondary hypogonadism (a problem with the brain signals directing testosterone production). Both produce low testosterone, but the underlying cause differs and affects how treatment is approached.

Common Symptoms of Low Testosterone

The symptoms of low testosterone span physical, mental, and sexual domains. Because many of these overlap with other conditions, low testosterone is frequently underdiagnosed or misattributed to depression, burnout, or simply getting older.

Physical symptoms include persistent fatigue, reduced muscle mass despite regular exercise, increased body fat (particularly around the abdomen), decreased bone density, and reduced body and facial hair. Sexual symptoms include low libido, erectile dysfunction, reduced ejaculate volume, and testicular shrinkage. Cognitive and emotional symptoms include brain fog, difficulty concentrating, depressed mood, irritability, and reduced motivation ( 1 ).

Not every man with low testosterone experiences all of these symptoms. Some men notice primarily the sexual effects; others notice mood changes first. The pattern varies by individual, age, and how far levels have dropped. That variability is one reason why clinical context matters alongside lab values.

What Causes Low Testosterone?

Causes of low testosterone fall into several categories. Age is a major factor: testosterone levels typically peak in early adulthood and decline at a rate of roughly 1 to 2 percent per year after age 30 ( 3 ). This gradual decline is normal, but it can accelerate significantly due to other factors.

Primary hypogonadism causes include testicular injury, infection (such as mumps orchitis), undescended testes, chemotherapy or radiation, and genetic conditions like Klinefelter syndrome. Secondary hypogonadism causes include obesity, type 2 diabetes, obstructive sleep apnea, chronic stress, opioid use, pituitary tumors, and other hormonal disorders such as hyperprolactinemia.

Lifestyle factors also play a meaningful role. Chronic sleep deprivation, excessive alcohol consumption, a sedentary lifestyle, and poor nutritional status are all associated with lower testosterone levels in population studies ( 2 ). These are modifiable factors, which means that addressing them may improve levels without medical intervention in some men.

How Low Testosterone Is Diagnosed

Diagnosis begins with a blood test measuring total serum testosterone. Because testosterone levels fluctuate throughout the day, peaking in the morning, testing is typically done between 7 and 10 a.m. after an overnight fast. A single low result is generally confirmed with a second test before any treatment decisions are made ( 2 ).

Additional labs may include free testosterone (the biologically active fraction not bound to proteins), sex hormone-binding globulin (SHBG), LH, FSH, prolactin, and a complete blood count. These results help distinguish primary from secondary hypogonadism and identify any underlying causes that need separate treatment.

Symptoms alone are not sufficient for a diagnosis of low testosterone, and a low lab value alone is not always sufficient either. The combination of both, in the absence of other explanations, is the standard clinical threshold for considering treatment.

Common Myths About Low Testosterone

One of the most common misconceptions is that low testosterone is exclusively an older man’s problem. While prevalence increases with age, secondary hypogonadism can affect men in their 20s and 30s, particularly those with obesity, poor sleep, or significant stress. Research suggests that rates of low testosterone in younger men may be increasing, though the reasons are still being studied ( 3 ).

Another myth is that low testosterone simply means low sex drive. While libido changes are common, they are only one aspect of a broader hormonal picture. Men often experience fatigue, mood changes, and body composition shifts long before they notice sexual symptoms.

A third misconception is that testosterone therapy is the only answer. For men with secondary hypogonadism driven by modifiable factors, lifestyle changes such as improved sleep, weight loss, and reduced alcohol intake can sometimes restore levels meaningfully without medical intervention. Treatment decisions should be individualized based on symptom severity, lab results, age, and health goals.

When to Get Tested

If you have been experiencing a persistent combination of the symptoms described above for several weeks or months, and those symptoms are not fully explained by another condition, a testosterone blood test is a reasonable first step. Discussing your symptoms with a primary care physician or a men’s health specialist will help determine whether testing is warranted and how to interpret the results in context.

Men with known risk factors, including obesity, type 2 diabetes, obstructive sleep apnea, or a history of testicular injury, may benefit from proactive monitoring even before noticeable symptoms develop. Early identification allows for earlier intervention and a greater opportunity to use lifestyle modification before considering medications.

If you are experiencing symptoms, speaking with a men’s health provider is the right first step. A proper diagnosis requires both lab work and a clinical conversation, not just a number on a lab report.

Emergency Notice: If you or someone else is experiencing a medical emergency, call 911 immediately. The information on this site is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment.