Low Testosterone Symptoms: What Could Be Causing Them

How Common Is Low Testosterone, and Who Gets It?

Testosterone deficiency is not rare, though prevalence estimates depend on the threshold used and the population studied. The European Male Ageing Study (EMAS), which measured testosterone in 3,219 community-dwelling men aged 40 to 79, found that only about 2% met criteria for late-onset hypogonadism when both low testosterone and specific symptoms were required 1. That number climbs sharply with age and body weight.

The Baltimore Longitudinal Study of Aging reported that roughly 20% of men over 60 and 50% of men over 80 had total testosterone below 325 ng/dL 2. These figures reflect a gradual decline of about 1% to 2% per year starting in the mid-30s, though the slope varies widely between individuals. Men who maintain a healthy weight and avoid medications known to suppress the hypothalamic-pituitary-gonadal (HPG) axis often preserve normal levels well into their 70s. Obesity is the single strongest modifiable predictor. Cross-sectional data from the Massachusetts Male Aging Study showed that a 4- to 5-point BMI increase produced a testosterone decline comparable to 10 years of aging 3.

This distinction matters clinically because it separates men who need testosterone replacement from those who may recover endogenous production by addressing the underlying cause.

What Are the Classic Symptoms of Low Testosterone?

The hallmark symptoms are decreased libido, erectile dysfunction, fatigue, and loss of muscle mass. Not all symptoms carry equal diagnostic weight. Sexual symptoms, particularly reduced morning erections and low desire, correlate most tightly with confirmed low testosterone levels.

EMAS investigators ranked symptom specificity and found that three sexual symptoms (poor morning erections, low sexual desire, and erectile dysfunction) were the only ones consistently associated with testosterone levels below 320 ng/dL 1. Non-sexual symptoms like sadness, fatigue, and reduced physical vigor appeared too, but only at much lower thresholds (below 230 ng/dL). This finding has practical implications: a man presenting with fatigue alone and a testosterone of 280 ng/dL may have a different root cause entirely.

Other recognized features include increased body fat (especially visceral adiposity), decreased bone mineral density, depressed mood, difficulty concentrating, and hot flashes in cases of severe deficiency. The Endocrine Society's 2018 clinical practice guideline emphasizes that clinicians should "make a diagnosis of hypogonadism only in men with symptoms and signs consistent with testosterone deficiency and unequivocally and consistently low serum testosterone concentrations" 4. A single low lab value, without symptoms, is not sufficient.

Primary Hypogonadism: When the Testes Are the Problem

Primary hypogonadism means the testes themselves cannot produce adequate testosterone, even when the brain sends the correct signals through luteinizing hormone (LH) and follicle-stimulating hormone (FSH). Lab work shows low testosterone with elevated LH and FSH, because the pituitary gland ramps up gonadotropin output in a failing attempt to stimulate the testes.

Klinefelter syndrome (47,XXY) is the most common congenital cause, affecting roughly 1 in 600 male births 5. Many men with Klinefelter syndrome go undiagnosed until they present with infertility or progressive testosterone deficiency in adulthood. Other congenital causes include cryptorchidism (undescended testes), myotonic dystrophy, and rare enzyme defects in testosterone biosynthesis.

Acquired causes are more varied. Testicular trauma, torsion, orchitis (including mumps orchitis), prior chemotherapy with alkylating agents, and pelvic radiation can all damage Leydig cell function. Bilateral orchiectomy for testicular cancer produces immediate, permanent hypogonadism requiring lifelong replacement. Hemochromatosis, an iron-overload disorder, can deposit iron in both the testes and the pituitary, causing a mixed picture 6.

The clinical approach to primary hypogonadism is straightforward in one sense: if testicular tissue is irreversibly damaged, testosterone replacement therapy (TRT) is the appropriate intervention. The challenge lies in identifying which patients still have reversible testicular suppression versus permanent Leydig cell failure, particularly when the cause is multifactorial.

Secondary Hypogonadism: When the Signal from the Brain Fails

Secondary (or central) hypogonadism results from insufficient gonadotropin-releasing hormone (GnRH) from the hypothalamus or insufficient LH/FSH from the pituitary. The lab pattern is low testosterone with low or inappropriately normal LH and FSH. This form is far more common than primary hypogonadism in clinical practice, especially in middle-aged and older men.

Obesity is the dominant driver. Excess adipose tissue increases aromatase activity, converting testosterone to estradiol, which then suppresses GnRH pulsatility through negative feedback 7. A study of 1,849 men in the Framingham Heart Study third-generation cohort found that each 1-point increase in BMI was associated with a roughly 2% decline in total testosterone 8. Weight loss can partially or fully reverse this. Bariatric surgery patients in one meta-analysis saw mean total testosterone increase by 8.7 nmol/L (approximately 251 ng/dL) after surgical weight loss 9.

Pituitary adenomas (particularly prolactinomas) are another important cause. A prolactin-secreting adenoma suppresses GnRH and can present with low libido, erectile dysfunction, and sometimes galactorrhea or visual field deficits. Screening for prolactin is recommended whenever secondary hypogonadism is identified 4.

Other causes include: Kallmann syndrome (congenital GnRH deficiency with anosmia), idiopathic hypogonadotropic hypogonadism, hyperprolactinemia from any cause, infiltrative diseases like sarcoidosis or histiocytosis, pituitary surgery or radiation, and severe traumatic brain injury affecting the hypothalamic-pituitary stalk.

Medications That Lower Testosterone

Several widely prescribed drug classes suppress testosterone production, and recognizing these is important because stopping or substituting the medication may restore endogenous levels without requiring TRT.

Opioids. Chronic opioid therapy is one of the most potent suppressors. A cross-sectional study of men on long-term opioid therapy found hypogonadism in 74% of participants, with mean total testosterone of 143 ng/dL 10. The mechanism involves direct suppression of GnRH pulsatility. Dr. Andre Guay, a clinical endocrinologist, described opioid-induced androgen deficiency as "the most under-recognized cause of secondary hypogonadism in modern practice" 10. Both duration and dose matter: higher morphine milligram equivalents correlate with deeper suppression.

Glucocorticoids. Chronic prednisone or dexamethasone use suppresses the entire HPG axis. Even inhaled corticosteroids at high doses may contribute.

GnRH agonists and antagonists. Used in prostate cancer treatment (leuprolide, degarelix), these agents intentionally ablate testosterone to castrate levels (below 50 ng/dL). This is pharmacologic, not pathologic, but the resulting symptoms are identical to severe hypogonadism.

Anticonvulsants. Carbamazepine, phenytoin, and phenobarbital increase sex hormone-binding globulin (SHBG), lowering free testosterone even when total testosterone appears borderline normal 11.

Ketoconazole and spironolactone. Both directly inhibit testicular steroidogenesis. Spironolactone also has anti-androgen receptor activity.

Chronic Illness, Sleep, and Metabolic Causes

Type 2 diabetes has a strong bidirectional relationship with low testosterone. The prevalence of hypogonadism among men with type 2 diabetes ranges from 25% to 40% in published cohorts 12. Insulin resistance appears to suppress LH pulse amplitude, and visceral fat amplifies the aromatase-mediated conversion described earlier. The Testosterone Trials (TTrials), a coordinated set of seven placebo-controlled trials in 790 men aged 65 and older with testosterone below 275 ng/dL, demonstrated that testosterone gel improved sexual function, walking distance, and mood but did not improve vitality as measured by the FACIT-Fatigue scale 13.

Obstructive sleep apnea (OSA) independently suppresses nocturnal testosterone secretion. Testosterone production peaks during sleep, and the intermittent hypoxia and sleep fragmentation of untreated OSA disrupt this pattern. Treatment with CPAP may partially restore levels in some men 14.

Chronic kidney disease (CKD), liver cirrhosis, HIV/AIDS, and hemochromatosis all contribute to testosterone deficiency through overlapping mechanisms: increased SHBG, decreased gonadotropin secretion, direct gonadal toxicity, or chronic inflammation. In advanced CKD, testosterone levels fall below 300 ng/dL in approximately 44% of men on dialysis 15.

The American Urological Association's 2018 guideline notes that clinicians should "evaluate for the underlying etiology before initiating testosterone therapy" and specifically screen for these reversible conditions 16.

How Is Low Testosterone Diagnosed?

Diagnosis requires two morning fasting total testosterone measurements below 300 ng/dL (10.4 nmol/L), drawn between 7:00 and 10:00 AM, combined with clinical symptoms. A single measurement is unreliable because testosterone fluctuates day to day by as much as 15% to 20%.

If total testosterone is borderline (between 250 and 400 ng/dL), measuring free testosterone or bioavailable testosterone provides additional clarity, particularly in men with conditions that raise SHBG (aging, liver disease, hyperthyroidism) or lower it (obesity, diabetes, hypothyroidism). Calculated free testosterone using the Vermeulen equation is more accurate than direct analog free testosterone assays, which are notoriously unreliable at low concentrations 4.

Once low testosterone is confirmed, the next step is distinguishing primary from secondary hypogonadism by measuring LH and FSH. Elevated gonadotropins point to testicular failure. Normal or low gonadotropins point to a hypothalamic or pituitary cause and should prompt measurement of prolactin, iron studies (ferritin and transferrin saturation), and possibly pituitary MRI.

Additional recommended labs include: complete blood count (to establish a baseline hematocrit before TRT), metabolic panel, lipid panel, PSA in men over 40, and in selected cases, karyotype (if Klinefelter syndrome is suspected) or pituitary function testing.

Treatment Options: From Lifestyle Changes to TRT

Treatment depends entirely on the cause. The Endocrine Society recommends against testosterone therapy in men who have not yet had a thorough diagnostic workup or in men seeking fertility, since exogenous testosterone suppresses spermatogenesis 4.

Reversible causes first. Weight loss of 5% to 10% of body weight can raise testosterone by 50 to 100 ng/dL in obese men with secondary hypogonadism. Opioid rotation or discontinuation, glucocorticoid dose reduction, and CPAP for sleep apnea should all be attempted before starting TRT.

Testosterone replacement therapy. For men with confirmed, symptomatic hypogonadism and no reversible cause, TRT is the standard of care. Delivery options include:

• Intramuscular injections (testosterone cypionate or enanthate, typically 100 to 200 mg every 1 to 2 weeks)
• Transdermal gels (testosterone 1.62% gel, applied daily)
• Transdermal patches
• Subcutaneous pellets (implanted every 3 to 6 months)
• Nasal gel (natesto, applied three times daily)
• Oral testosterone undecanoate (Jatenzo, taken twice daily with food)

The TRAVERSE trial (N=5,246), published in the New England Journal of Medicine in 2023, was the first large cardiovascular safety trial of TRT. It found that testosterone replacement in men aged 45 to 80 with hypogonadism and preexisting or high risk of cardiovascular disease did not increase the incidence of major adverse cardiovascular events compared to placebo (hazard ratio 0.96 to 95% CI 0.78 to 1.17) 17. This resolved a long-standing safety concern, though it did confirm an increased risk of atrial fibrillation, acute kidney injury, and pulmonary embolism.

Clomiphene citrate (off-label). For younger men with secondary hypogonadism who want to preserve fertility, clomiphene citrate 25 to 50 mg daily stimulates endogenous LH and FSH secretion. A retrospective series of 86 men treated with clomiphene showed a mean testosterone increase from 228 ng/dL to 612 ng/dL at a median follow-up of 19 months 18.

Monitoring and Follow-Up on TRT

Men starting TRT require structured follow-up. The Endocrine Society recommends checking testosterone levels, hematocrit, and PSA at 3 to 6 months and then annually 4. Target trough testosterone on therapy is 400 to 700 ng/dL. Hematocrit above 54% warrants dose reduction or phlebotomy, as polycythemia is the most common adverse effect of TRT.

PSA should be measured at baseline and monitored. TRT is contraindicated in men with untreated breast or prostate cancer, hematocrit above 50% at baseline, untreated severe obstructive sleep apnea, uncontrolled heart failure, or a desire for fertility in the near term.

Bone density testing (DXA scan) is recommended for men with severe or prolonged hypogonadism, as testosterone deficiency is a recognized cause of male osteoporosis. The Endocrine Society notes that "testosterone treatment of men with osteoporosis and testosterone deficiency increases spine and hip bone mineral density" 4.

Patients should expect measurable improvements in libido and energy within 3 to 6 weeks, with body composition changes (increased lean mass, decreased fat mass) becoming apparent by 12 to 16 weeks. Maximal effects on bone density require 24 to 36 months of consistent therapy.