Signs of Low Testosterone: Symptoms, Causes, and When to Get Tested

If you want the answer first: the symptoms most specifically associated with low testosterone in published guidelines are reduced sexual desire (libido), reduced spontaneous erections, and reduced morning erections. Other commonly reported symptoms — fatigue, low mood, difficulty concentrating, loss of muscle mass, increased body fat — are real but non-specific, meaning they show up in many unrelated conditions.

Because symptoms overlap so heavily with sleep deprivation, depression, thyroid disorders, anemia, and ordinary aging, no reputable guideline lets you diagnose low testosterone from how you feel. The Endocrine Society's 2018 Clinical Practice Guideline is explicit: diagnosis requires both consistent symptoms and a blood test showing unequivocally low testosterone, confirmed on a repeat measurement. That is the bar. Everything below explains how to meet it responsibly.

Clinicians generally group the signs of possible testosterone deficiency into more specific and less specific categories. This grouping comes from the symptom clusters described in the Endocrine Society guideline and the American Urological Association's evaluation guidance.

More specific (sexual) symptoms

• Lower sexual desire (libido)
• Fewer spontaneous or morning erections
• Erectile difficulties (though these have many causes, including vascular and psychological)

Less specific symptoms

• Persistent fatigue or low energy
• Depressed mood, irritability, or reduced motivation
• Difficulty concentrating ("brain fog")
• Loss of muscle mass or strength
• Increased body fat
• Reduced body or facial hair (over longer periods)

The important caveat: the less-specific symptoms are common in the general population and are frequently driven by something other than testosterone. That is exactly why a test — not a checklist — is the deciding factor. A symptom questionnaire can prompt you to get evaluated, but it cannot diagnose you.

Low testosterone is broadly divided by where the problem originates. Clinicians call these primary (the testes), secondary (the pituitary/hypothalamus signaling), and contributing or reversible factors.

Primary hypogonadism (testicular)

• Klinefelter syndrome and other genetic conditions
• Prior testicular injury, surgery, infection (e.g., mumps orchitis), or undescended testes
• Chemotherapy or radiation

Secondary hypogonadism (pituitary/hypothalamic)

• Pituitary tumors or disorders
• Certain medications, including long-term opioids and some corticosteroids
• Elevated prolactin

Contributing and often-reversible factors

• Obesity — strongly associated with lower measured testosterone
• Poorly controlled type 2 diabetes and metabolic syndrome
• Obstructive sleep apnea and chronic sleep deprivation
• Acute illness (testosterone can dip during illness and recover afterward, which is one reason testing during illness is discouraged)
• Heavy alcohol use

This last group matters because addressing the underlying cause — weight, sleep, glucose control, a contributing medication — can change the picture. A good clinical evaluation looks for these before defaulting to lifelong treatment.

Here is where internet numbers cause the most confusion. Testosterone is reported in nanograms per deciliter (ng/dL) for total testosterone in the U.S. Reference ranges differ between laboratories and between assay methods, so the same blood draw can fall inside one lab's "normal" and below another's.

With that caveat, some published anchors:

• A frequently cited lower bound for total testosterone is roughly 264-300 ng/dL; the Endocrine Society guideline references a lower limit in this vicinity for healthy young men, and notes that local lab reference ranges should be used when available.
• The American Urological Association's guidance has used 300 ng/dL as a common reference threshold for considering low testosterone, paired with symptoms.
• Diagnosis hinges on a morning sample, confirmed by a second morning sample, because a single result can be misleading.

When total testosterone is borderline, clinicians may measure free testosterone (the unbound, biologically active fraction) and sex hormone-binding globulin (SHBG), plus LH and FSH to help locate the cause. A meaningful diagnosis is a clinical judgment that combines the number, the timing, the repeat test, and the symptoms — not a single value typed into a search bar.

Done correctly, testing is straightforward:

1. Timing. Blood is drawn in the morning, typically before 10-11 a.m., when testosterone peaks.
2. Confirmation. An abnormal result is repeated on a separate morning before any diagnosis, since day-to-day variation is significant.
3. Not during acute illness. Testing is generally deferred until you've recovered, because illness can transiently lower levels.
4. Follow-up labs if needed. Depending on results, a clinician may add free testosterone, SHBG, LH, FSH, prolactin, or other workup to find the cause.

Telehealth platforms can make the logistics easier — ordering labs, routing you to a partner lab or at-home option, and connecting you with a licensed clinician to interpret results. What they cannot do is skip the clinical step. Any legitimate provider still requires an evaluation by a licensed clinician before prescribing, and that's the legal and medical norm in the United States.

If testing confirms genuinely low testosterone and a clinician determines treatment is appropriate, testosterone replacement therapy (TRT) is one option, available in forms such as injections, gels, and others. We are deliberately not describing dosing or outcomes here, because that is a clinical decision specific to each person.

A few facts worth knowing before that conversation:

• FDA-approved testosterone products carry a class warning about possible cardiovascular risk signals and about blood-pressure increases noted on current labeling; the evidence has been debated and continues to be studied. Your clinician weighs this against your individual situation.
• Testosterone can suppress sperm production and fertility. Men who want to preserve fertility should raise this before starting.
• Compounded testosterone is not FDA-approved. Compounded preparations are made by pharmacies for individual patients and have not been evaluated by the FDA for safety, efficacy, or manufacturing quality the way FDA-approved products are. If a provider offers a compounded option, ask why and understand the trade-offs.
• Monitoring is part of treatment. Clinicians typically monitor labs (including hematocrit and PSA where appropriate) on therapy.

None of the above is a recommendation for or against treatment. It is context so you can ask better questions. Testosterone is a controlled substance; it should only ever be obtained through a licensed provider with a valid prescription — never through grey-market sellers, "research chemicals," or any source that skips a consultation.

In the spirit of an honest review site: we can verify that the providers named in the comparison table operate as telehealth or telehealth-adjacent services that deliver care through licensed clinicians, and that legitimate prescribing in the U.S. requires an evaluation. What we cannot verify in a static article is each provider's current pricing, lab partners, geographic availability, or whether a specific service or medication is offered at the moment you read this — those change frequently and are controlled entirely by the provider. Treat every price and feature as provider-attributed and confirm it at the source before acting. We do not accept payment for placement, and inclusion here is editorial, not an endorsement of any provider's product or claims.