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**Low testosterone (also called male hypogonadism or "low T") is a condition in which the body does not make enough testosterone *and* a man has symptoms tied to that deficiency.** A low number on a blood test by itself is not the diagnosis — clinicians require both consistently low testosterone and matching symptoms before treating (Testosterone Deficiency: AUA Guideline, 2018; Endocrine Society Clinical Practice Guideline, J Clin Endocrinol Metab 2018).
Testosterone is the main male sex hormone (androgen). It is produced chiefly by the Leydig cells of the testes under the control of two pituitary hormones — luteinizing hormone (LH) and follicle-stimulating hormone (FSH) — which are themselves driven by gonadotropin-releasing hormone (GnRH) from the hypothalamus. This chain is called the hypothalamic-pituitary-gonadal (HPG) axis. Testosterone drives sperm production, sex drive, erections, muscle and bone mass, red blood cell production, body hair, and aspects of mood and energy. When any link in the HPG axis fails, testosterone falls.
Doctors classify low testosterone by *where* the breakdown occurs:
This distinction matters because it changes the workup (a young man with primary hypogonadism may warrant genetic testing; secondary hypogonadism may prompt brain imaging) and the treatment goals (testosterone replacement versus fertility-preserving options).
In medical records, the condition is coded under ICD-10 E29.1 (testicular hypofunction) and E23.0 (hypopituitarism, for central causes), with the broader category E29 covering testicular dysfunction.
Causes fall along the primary/secondary split.
Causes of primary (testicular) hypogonadism:
Causes of secondary (central) hypogonadism:
Functional and age-related decline. Testosterone falls gradually with age. The Endocrine Society notes this age-related decline and cautions against treating older men on the basis of an age-adjusted "low" number alone without clear symptoms and consistently low levels. Obesity is one of the strongest reversible contributors, because excess fat tissue increases conversion of testosterone to estrogen and lowers sex hormone-binding globulin (SHBG).
Who is most at risk? Men who are obese or have type 2 diabetes or metabolic syndrome; men on long-term opioids or glucocorticoids; men with a history of testicular problems, chemotherapy, or pelvic radiation; men with pituitary disease; and men with HIV or other chronic illness. Risk also rises with age, though aging alone is not a disease.
Symptoms are often nonspecific, which is exactly why a blood test is required to confirm them. The Endocrine Society and AUA distinguish symptoms that are relatively *specific* to testosterone deficiency from those that are *suggestive* but common to many conditions.
More specific symptoms:
Less specific symptoms:
Because fatigue, low mood, and reduced libido overlap heavily with depression, thyroid disease, anemia, sleep apnea, and ordinary stress, symptoms alone cannot diagnose low testosterone.
Diagnosis rests on two pillars: consistent symptoms plus consistently low blood testosterone. Both guidelines are emphatic that one without the other is not a diagnosis.
Timing and confirmation of the blood test. Testosterone follows a daily rhythm, peaking in the morning, and varies day to day. Both the AUA and the Endocrine Society recommend measuring fasting total testosterone in the early morning (generally before 10–11 a.m.), and confirming a low result with a second morning measurement on a separate day before diagnosing. A single low value should not be acted on.
Thresholds. The AUA suggests using a total testosterone below 300 ng/dL as a reasonable cutoff supporting the diagnosis, chosen to balance benefit and risk based on the available literature (AUA Guideline, 2018). The Endocrine Society frames the diagnosis as "unequivocally and consistently low" testosterone with matching symptoms rather than a single universal number, because reference ranges vary by assay and laboratory. Reported ranges differ between labs, so results should be interpreted against the specific assay used.
Free testosterone. Most testosterone in blood is bound to SHBG and albumin; only a small fraction is "free" and active. When a total testosterone result is borderline, or when a man has a condition that alters SHBG (obesity, diabetes, thyroid disease, older age, certain medications), the Endocrine Society recommends measuring free testosterone with an accurate method (equilibrium dialysis or a validated calculation from total testosterone, SHBG, and albumin).
Finding the cause. Once low testosterone is confirmed, clinicians measure LH and FSH to separate primary (high LH/FSH) from secondary (low or normal LH/FSH) hypogonadism. Depending on the picture, additional tests may include prolactin, iron studies (ferritin/transferrin saturation) for hemochromatosis, karyotype for suspected Klinefelter syndrome, and pituitary MRI for unexplained secondary hypogonadism. A semen analysis is added when fertility is a concern.
Treatment is matched to the cause, the man's symptoms, and his fertility goals. Reversible contributors should be addressed first.
For many men — especially those with obesity, metabolic syndrome, or sleep apnea — testosterone can improve without hormone therapy:
There are no over-the-counter supplements proven to reliably raise testosterone or treat hypogonadism. "Testosterone booster" products are not FDA-approved to treat the condition, are not regulated as drugs, and should not replace evaluation by a clinician. Vitamin D or zinc correction may help only if a true deficiency exists.
When low testosterone is confirmed and symptomatic, and reversible causes are addressed, the mainstay is testosterone replacement therapy. The goal is to raise testosterone into the mid-normal range and relieve symptoms. FDA-approved formulations include:
Important safety points. TRT is not appropriate for men who want to preserve fertility in the near term, because it suppresses the body's own LH/FSH and sperm production. It is generally contraindicated in men with untreated prostate or breast cancer and used cautiously in those with severe untreated sleep apnea, uncontrolled heart failure, elevated red blood cell counts (hematocrit), or a recent cardiovascular event. Monitoring typically includes testosterone levels, hematocrit (testosterone can thicken the blood, raising clot risk), and PSA and a prostate exam per guideline schedules.
Cardiovascular safety. The large randomized TRAVERSE trial (Lincoff et al., N Engl J Med 2023;389:107–117) enrolled 5,246 men aged 45–80 with hypogonadism and preexisting or high cardiovascular risk, and over a mean of about 27 months found that testosterone gel was noninferior to placebo for major adverse cardiac events — the composite of cardiovascular death, nonfatal myocardial infarction, and nonfatal stroke (HR 0.96; 95% CI 0.78–1.17; P<0.001 for noninferiority). The trial did, however, show higher rates of atrial fibrillation, pulmonary embolism, and acute kidney injury in the testosterone group, so it does not give testosterone a clean bill of cardiovascular health. Investigators stressed that this reassurance on major cardiac events applies to men with a genuine indication and is not a justification for prescribing testosterone broadly to aging men without confirmed deficiency.
For men with secondary hypogonadism who want to conceive, doctors may use therapies that stimulate the man's *own* testosterone and sperm production instead of replacement testosterone:
These are managed by endocrinology or urology/reproductive specialists.
Genetic causes such as Klinefelter syndrome cannot be prevented, but a large share of acquired and functional low testosterone is preventable or modifiable. Maintaining a healthy weight, staying physically active, treating sleep apnea, limiting alcohol, avoiding anabolic steroid abuse, and using opioids only when necessary all protect the HPG axis. Good control of diabetes and metabolic syndrome helps as well.
For men on testosterone therapy, long-term management means staying in the treatment range while watching for side effects — particularly a rising hematocrit, prostate changes, acne or fluid retention, and breast tenderness. Periodic blood work and follow-up keep therapy safe and effective. Bone density may be monitored in men with long-standing deficiency, since low testosterone is a recognized risk factor for osteoporosis.
See a clinician if you have ongoing symptoms such as low sex drive, erectile dysfunction, unexplained fatigue, loss of muscle, or depressed mood — both to test for low testosterone and to rule out other conditions that mimic it.
Seek prompt or urgent care for "red flag" features, which can signal a serious underlying cause:
A man planning to father children should raise fertility *before* starting any testosterone therapy, since replacement testosterone suppresses sperm production.
The outlook for low testosterone is generally favorable. When a reversible cause — obesity, sleep apnea, opioids, or another illness — is identified and corrected, testosterone often recovers without lifelong therapy. When replacement therapy is appropriately prescribed and monitored, most men experience improvement in libido, energy, mood, muscle mass, and bone density, and current evidence including the TRAVERSE trial does not show an increased risk of major adverse cardiac events in properly selected, monitored patients — though that same trial found higher rates of atrial fibrillation and pulmonary embolism on testosterone, which is part of why ongoing monitoring matters. Untreated, long-standing low testosterone can contribute to bone loss, anemia, reduced muscle mass, and impaired quality of life, which is why diagnosis and appropriate management matter. Genetic conditions such as Klinefelter syndrome require lifelong care but are very manageable with treatment.
Is low testosterone just a normal part of getting older? Testosterone does decline gradually with age, but a low number alone is not a disease. Guidelines recommend treating older men only when they have both clearly low testosterone confirmed on repeat morning testing *and* matching symptoms — not on the basis of age or a borderline result (Endocrine Society Guideline, 2018).
What testosterone level is considered "low"? The AUA suggests a total testosterone below 300 ng/dL as a reasonable cutoff supporting the diagnosis, measured fasting in the early morning and confirmed on a second day. Reference ranges vary by laboratory and assay, and borderline results often warrant a free testosterone measurement, so results should be interpreted by a clinician (AUA Guideline, 2018).
Will testosterone therapy make me infertile? Replacement testosterone usually suppresses the body's own LH and FSH, which lowers sperm production and can cause temporary or, less often, lasting infertility. Men who want to conceive should discuss fertility-preserving options such as hCG, gonadotropins, or clomiphene before starting standard testosterone therapy.
Do over-the-counter "testosterone boosters" work? No supplement is FDA-approved to treat low testosterone, and these products are not regulated as drugs. There is no reliable evidence they raise testosterone enough to treat hypogonadism. Correcting a true vitamin D or zinc deficiency, losing weight, and treating sleep apnea are the evidence-based "natural" levers.
Is testosterone therapy safe for my heart? The large randomized TRAVERSE trial (Lincoff et al., N Engl J Med 2023) found testosterone therapy did not increase major adverse cardiac events (cardiovascular death, heart attack, or stroke) compared with placebo in hypogonadal men at high cardiovascular risk over roughly 27 months. It did, however, find more cases of atrial fibrillation and pulmonary embolism in the testosterone group, so it is not a blanket guarantee of heart safety. That reassurance applies to men with a confirmed diagnosis under proper monitoring, not to using testosterone without a medical indication.
*This page is for general education and is not medical advice. Talk with a qualified clinician about diagnosis and treatment for your situation.*
FDA-approved testosterone replacement therapy (TRT) is available in several forms: transdermal gels and solutions, skin patches, intramuscular or subcutaneous injections (testosterone cypionate, enanthate, or undecanoate), an oral capsule (testosterone undecanoate, e.g., Jatenzo, Tlando, Kyzatrex), surgically implanted pellets (Testopel), and a nasal gel (Natesto). On February 28, 2025, the FDA issued class-wide labeling changes: based on the large TRAVERSE trial (5,204 men with hypogonadism and high cardiovascular risk, in which major adverse cardiac events occurred at a comparable rate of about 7% with testosterone gel and about 7% with placebo), it removed the prior Boxed Warning language about increased cardiovascular risk, added a warning about possible increases in blood pressure, and retained a "Limitation of Use" stating these products are not established as safe or effective for low testosterone due solely to aging. TRT is FDA-approved only for men with hypogonadism caused by a defined medical condition, not for age-related decline alone. All testosterone products are controlled substances and require a prescription; "low-T" clinics, online prescribers, and over-the-counter "testosterone boosters" or supplements are not FDA-evaluated for this use and can be unsafe. Off-label options a clinician may discuss for younger men wishing to preserve fertility include clomiphene citrate and human chorionic gonadotropin (hCG). Any treatment decision should be made with a qualified clinician after proper diagnosis and monitoring. This information is educational and is not a substitute for professional medical advice.
It depends on the cause. When low testosterone is driven by a reversible (functional) issue such as obesity, poorly controlled type 2 diabetes, sleep apnea, certain medications, or chronic stress, treating that root cause can raise levels naturally without lifelong therapy. When it stems from permanent damage to the testicles, pituitary, or hypothalamus (organic hypogonadism), it generally cannot be cured but can be effectively managed with testosterone therapy. A clinician should determine which type you have before deciding on treatment.
The most specific symptoms are sexual: low libido, reduced spontaneous or morning erections, and difficulty achieving or maintaining an erection. Other common signs include fatigue, low mood, reduced muscle mass and strength, increased body fat, loss of bone density, and sometimes breast tenderness or shrinking testicles. Because these symptoms overlap with many other conditions, they should be confirmed with a blood test rather than assumed.
Low testosterone falls into two broad categories. Primary hypogonadism comes from problems in the testicles themselves, such as injury, infection, chemotherapy, or genetic conditions like Klinefelter syndrome. Secondary hypogonadism comes from the pituitary gland or hypothalamus and is often linked to obesity, type 2 diabetes, sleep apnea, chronic illness, certain medications (including opioids and steroids), and the gradual age-related decline that begins around the late 30s.
Major guidelines generally consider a total testosterone below about 300 ng/dL as low, while the Endocrine Society uses a threshold around 264 ng/dL. However, a number alone is not enough to diagnose low testosterone. A diagnosis requires both a low reading and characteristic symptoms, since normal ranges and lab assays vary; your clinician should interpret your specific results.
Diagnosis requires symptoms plus blood testing, not symptoms alone. Because testosterone peaks in the morning and naturally fluctuates, guidelines call for at least two separate blood samples drawn in the early morning (typically 7 to 10 AM) on different days. If levels are low, doctors often add tests such as luteinizing hormone (LH) and prolactin to identify whether the problem originates in the testicles or the pituitary gland.
The main medical treatment is testosterone replacement therapy, available as skin gels, patches, intramuscular or subcutaneous injections, implantable pellets, nasal gel, and oral forms. Doctors typically aim for testosterone in the mid-normal range and recheck levels within 3 to 6 months. If a reversible cause like obesity or sleep apnea is found, addressing that first may restore levels without therapy, so treatment should always be individualized with a clinician.
Yes, standard testosterone replacement therapy usually lowers sperm production and can cause temporary infertility, because supplemental testosterone suppresses the brain signals that drive sperm production. In many men sperm production recovers within several months after stopping, though recovery is not guaranteed and is less likely with older age or long-term use. Men who want to preserve fertility should tell their doctor, as alternatives like clomiphene can raise testosterone while protecting sperm production.
Testosterone does naturally decline with age, dropping roughly 1% per year starting in a man's late 30s, so some reduction is expected. However, a level that falls into the low range alongside bothersome symptoms is not something you simply have to accept and may warrant evaluation. A clinician can distinguish normal age-related change from clinically significant low testosterone that could benefit from treatment.
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This page is for general information and is not medical advice. Always consult a qualified clinician about diagnosis and treatment. Individual results vary.