Low Testosterone: Real Symptoms, What the Lab Measures and What Actually Changes With Treatment

En español: cuáles síntomas sí apuntan a la testosterona baja, cómo se hace bien el examen (mañana, ayunas, dos veces), qué significan los números, qué mejora con el tratamiento según los ensayos más grandes, qué no mejora y los riesgos confirmados en 2023 y 2024.

"I think my testosterone is low." It is one of the sentences we hear most often, and it almost always arrives before any lab result. It arrives because an ad promised energy, muscle and desire in a bottle. It arrives because 45 feels different from 30. And it arrives because on the internet, every kind of tiredness gets explained by one hormone.

This article does the opposite of the ad. It tells you which symptoms actually point to testosterone and which do not. It explains how the test is done properly, why a single result is not enough, and what number counts as "low" according to reference laboratories. And it walks through the largest trials that exist to show what improves with treatment, what does not, and which risks were confirmed in 2023 and 2024. If you want the big picture on male hormones, it is in Men's hormonal health. Here we go specific: the diagnosis and what changes afterward.

The real symptoms: which ones actually point to testosterone

The symptom list that circulates online is long: fatigue, low mood, poor focus, less muscle, more belly, irritability, bad sleep. The problem is that this list describes almost any adult with stress, short sleep and extra weight. If everything is a symptom, nothing is.

The study that brought order is called EMAS (European Male Ageing Study). A European group surveyed 3,369 men aged 40 to 79, measured morning testosterone by mass spectrometry and cross-checked the numbers against symptoms. The result, published in the New England Journal of Medicine in 2010, was clear: of all the symptoms evaluated, only three had a "syndromic" relationship with low testosterone, meaning they appeared together and in proportion to how far the hormone fell.

• Fewer morning erections (or none).
• Lower sexual desire.
• Erectile dysfunction.

Fatigue, depression and difficulty with vigorous activity were also related to testosterone, but weakly and non-specifically: they show up just as often in men with normal hormone levels. That is why the authors defined "late-onset hypogonadism" this way: at least three sexual symptoms plus a total testosterone below 11 nmol/L (about 320 ng/dL) and a free testosterone below 220 pmol/L (64 pg/mL).

Translated: if your main complaint is tiredness and you have no sexual symptoms at all, the chance that testosterone is the cause is low. If you have all three sexual symptoms, the chance rises a lot, and that is when measuring is worth it.

How many men truly have it low?

This number surprises people because marketing suggests half of men over 40 are low. What is common is a low number on a single isolated test without symptoms, or symptoms without a low number. What is rare is having both at once, which is the only thing that is called hypogonadism.

A Boston study (BACH, 1,822 men from a racially and ethnically diverse sample) found that the most important factor tied to low testosterone was not age but the waist: for every extra 10 cm of waist circumference, the odds of low testosterone rose 75%. Age counted too (36% more per decade), but the waist weighed more. Hold on to that fact, because it explains the section on weight and GLP-1 later on.

What the lab measures and how to do it right

The Endocrine Society guideline (2018) is the reference endocrinologists use in the United States. Its diagnostic rules fit in five lines, and nearly all of them get broken in commercial practice.

1. Symptoms first, then the test

The guideline recommends diagnosing hypogonadism only in men with compatible symptoms and signs and with "unequivocally and consistently low" testosterone. It does not recommend testing men without symptoms "to see where they stand." A low number without symptoms is not a disease.

2. Total testosterone, in the morning, fasting

Testosterone has a daily rhythm: it is highest between 7 and 10 a.m. and falls through the day, especially in younger men. Eating also lowers it temporarily. That is why the initial test is total testosterone, in the morning, fasting. An afternoon test after lunch can come back "low" in a completely normal man.

3. Two measurements, not one

The guideline recommends confirming with a second fasting morning measurement on a different day. About a third of men with a low first value have a normal second one. The large trials required two values at least 48 hours apart, and that is what your physician should order before talking about treatment.

4. Free testosterone only in specific cases

About 98% of testosterone travels bound to proteins, mostly SHBG (sex hormone-binding globulin). "Free" testosterone is the fraction that can enter cells. The guideline says to measure it only when total is near the lower limit or when there is a condition that alters SHBG: obesity, type 2 diabetes, hypothyroidism, liver disease, certain medications. In those cases, total is misleading. And if it is measured, it should be by equilibrium dialysis or a validated formula, not the cheap direct assays the guideline considers unreliable.

5. If it is low, look for the cause

This is the difference between medicine and sales. A confirmed low testosterone forces the question: why? LH and FSH (the brain's signals to the testes) are ordered to tell whether the problem is in the testes or the pituitary, plus prolactin, and sometimes iron studies, an MRI or other tests. If nobody asked why it was low and only offered you treatment, they skipped the most important step.

Before any treatment, the guideline also recommends measuring hematocrit and, depending on age and risk, PSA, because both change with testosterone and are monitored during treatment.

How to read your numbers

Every lab prints its own "normal range," and for years those ranges varied so much that the same man came back "low" at one lab and "normal" at another. In 2017 an international group took four cohorts from the United States and Europe (9,054 men), calibrated the assays against the CDC reference method and published a harmonized range for healthy, non-obese men aged 19 to 39.

Three warnings about this table. First: 264 ng/dL is the harmonized limit for the reference method; the large clinical trials used 275 or 300 ng/dL as their entry cutoff, and the guideline accepts that margin. Second: SHBG falls with obesity and insulin resistance, so an overweight man can have a "low" total with a normal free level, and in that case he does not have hypogonadism, he has excess weight. Third: a value is not a diagnosis. It is read together with the symptoms, the second sample, the LH and the history.

Why it drops: age, belly fat, sleep and medications

Testosterone falls with age, but less than people think: in healthy men, about 1% a year after 40. What really sinks it are other things, and nearly all of them can be changed.

Belly fat

Fat tissue converts testosterone into estrogen with an enzyme called aromatase. More belly fat, more conversion, less testosterone, and a "there is enough" signal that switches off the pituitary. Obesity also lowers SHBG, and insulin resistance makes the whole circuit worse. This is called functional hypogonadism, and the key word is "functional": it reverses when the cause changes.

Sleep and apnea

Testosterone is produced mostly during deep sleep. Sleeping five hours, working nights or having untreated sleep apnea lowers it measurably. A man who snores, wakes up tired and has a low level needs a sleep study before hormone therapy.

Medications and substances

Opioids (including chronic use for pain), corticosteroids, some antidepressants, excess alcohol and, above all, anabolic steroids or unsupervised testosterone "cycles" shut down the body's own production. That last case is increasingly common in clinic: the man who used gym testosterone and now has a dormant axis. That is hypogonadism too, but a caused one.

Diseases

Type 2 diabetes, liver or kidney disease, HIV, hemochromatosis, pituitary tumors, prior chemotherapy, testicular injury. Each has its own management, and none is solved with a gel.

What changes with treatment

This is where the ads and the trials part ways. The two studies that carry the most weight are the Testosterone Trials (T Trials, 2016) and TRAVERSE (2023). Here is what they found.

Sexual function: moderate improvement

The T Trials assigned 790 men aged 65 or older, with testosterone below 275 ng/dL and symptoms, to testosterone gel or placebo for one year. Treatment raised the hormone to the mid-range of a man aged 19 to 40. Sexual activity, desire and erectile function improved significantly versus placebo. The authors describe it as a "moderate" benefit, and it is the most consistent finding in the entire literature.

Mood: slight improvement

Treated men reported slightly better mood and fewer depressive symptoms. The effect was small and is not the same as treating depression.

Walking: better in the pooled group, not in the main group

The share of men who improved by at least 50 meters on the 6-minute walk test was 20.5% on testosterone versus 12.6% on placebo when all participants were pooled, but it was not significant in the group designed to measure it.

Vitality and energy: no improvement

This is the finding almost nobody repeats. The number one symptom men ask for testosterone for, tiredness, is precisely the one that did not improve in the controlled trial. If your complaint is energy, the more likely answer is in sleep, weight, thyroid, iron or mood, not testosterone.

Body composition: less fat, more lean mass

A meta-analysis of 32 observational studies (4,513 men with diagnosed deficiency) found a weight reduction of about 3.5 kg and 6 cm of waist at 24 months, with less fat, more lean mass and better glucose and lipids. These are observational studies, not controlled ones, and the authors themselves call for a trial designed to confirm it. Controlled trials show the change in composition (less fat, more muscle) but a much more modest effect on total weight.

Bone and anemia

In the T Trials, spine bone density improved and unexplained anemia was corrected in more treated men. But, as you will see below, more density did not translate into fewer fractures.

What does not improve, and the confirmed risks

For a decade the question was whether testosterone harms the heart. TRAVERSE was designed to answer it: 5,246 men aged 45 to 80 with cardiovascular disease or high risk, symptoms and two testosterone levels below 300 ng/dL, assigned to testosterone gel or placebo, with an average follow-up of 33 months.

That is the good news, and it is real. But the same study found signals that do matter:

• Atrial fibrillation: more frequent with testosterone (3.5% versus 2.4%).
• Acute kidney injury: 2.3% versus 1.5%.
• Pulmonary embolism: 0.9% versus 0.5%.
• Fractures: in the TRAVERSE fracture substudy (5,204 men, 3.2 years), clinical fractures occurred in 3.50% of treated men versus 2.46% on placebo (hazard ratio 1.43). That is, more fractures, not fewer, despite better bone density.
• High hematocrit: testosterone raises red blood cells. It is the most common adverse effect and the reason blood is checked every 3 to 6 months in the first year.
• Blood pressure: the ambulatory monitoring studies the FDA required showed blood pressure increases with several products.
• Fertility: external testosterone shuts down sperm production. In a 2024 trial, men on injected testosterone dropped their sperm concentration and total count within 24 weeks. If you want children, this is not your option.
• Prostate: there is no evidence it causes cancer, but it can accelerate an existing one, which is why PSA is monitored.

And one risk that does not appear in the table: dependence. After months of external testosterone, your own production is switched off. Stopping without a plan produces a sharp drop with symptoms worse than the original ones. Treatment is started knowing how it ends.

What the FDA says in 2025

In February 2025 the FDA ordered label changes for all testosterone products. It removed the language about cardiovascular risk from the boxed warning, because TRAVERSE did not confirm it. It added the TRAVERSE results to the labels. It added a new warning about blood pressure increases. And it kept the "limitation of use": testosterone products are approved for hypogonadism caused by specific medical conditions, not for "age-related" low testosterone without an identified cause.

That last line is the one that contradicts marketing the most. The FDA still says that "age-related" low testosterone is not, on its own, an approved indication. A physician can treat it if they consider it justified in your case, but should explain that it is outside the label indication and why.

Weight, GLP-1 and testosterone: the link almost nobody explains

Go back to the Boston finding: the waist weighed more than age. And to the 2013 meta-analysis: losing weight raises testosterone without touching any hormone. In many overweight men, the treatment for low testosterone is not testosterone; it is losing weight, sleeping and moving, with a physician who confirms there is no other cause.

There is a recent finding pointing the same way. In a 2024 trial of 25 men with obesity, type 2 diabetes and functional hypogonadism, semaglutide (a GLP-1) raised total testosterone and improved symptoms over 24 weeks, just as injected testosterone did, with one difference: the men on semaglutide improved their sperm quality, and the men on testosterone worsened it. It is a small, open-label study and does not change guidelines, but it shows the mechanism in action: remove the fat and the axis wakes up.

That is why at SCTS1 the order is this. Once you start your program, a licensed physician reviews your case — habits, stress, sleep and medical history — and orders labs only if they consider it necessary. If testosterone comes up in the conversation, that physician decides whether to measure it, how (morning, fasting, twice) and what to do with the result. Sometimes the answer is a weight-management program. Sometimes it is treating sleep. Sometimes it is hormone therapy with monitoring. And sometimes it is "your hormones are fine, the problem is something else." Eligibility is determined by medical evaluation.

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What this evidence does NOT say

It does not say testosterone is useless. It says it works for what it works for: sexual function, mood to some degree, body composition, bone, anemia. And that it did not work for tiredness in the controlled trial.

It does not say it is dangerous for the heart. TRAVERSE showed it does not increase heart attacks or strokes in at-risk men. It says it does increase arrhythmia, embolism, kidney injury and fractures, and that this is weighed case by case.

It does not say a low number is a disease. Without symptoms and without a second sample, a number is a number.

It does not say age justifies treatment. The FDA still has not approved testosterone for "age-related" low levels, and the European study found that at 40 almost nobody is truly low.

It does not say weight loss replaces treatment for everyone. A man with high LH and testes that do not produce will not fix it with diet. That is why the cause has to be found.

Who is this NOT for?

• Men who want children in the next few years: external testosterone shuts down sperm production.
• Men with active or suspected prostate or breast cancer.
• Men with unexplained high hematocrit, severe untreated sleep apnea or decompensated heart failure.
• Men with a single "low" afternoon test and no sexual symptoms: repeat it properly first.
• Men whose only symptom is tiredness: sleep, thyroid, iron, mood and weight come first.
• Anyone who used "cycles" and wants medical testosterone to fix the shut-down axis without evaluation: that case needs different management.
• Anyone under 18.
• Anyone who wants a guarantee of energy, muscle or youth. It does not exist.

Frequently asked questions

What are the real symptoms of low testosterone?

The three that are consistently associated are fewer morning erections, lower sexual desire and erectile dysfunction. Fatigue, low mood and loss of strength are related but non-specific: they show up just as often with normal hormone levels.

How is the testosterone test done properly?

Total testosterone in the morning (7 to 10 a.m.), fasting, with a second sample on another day to confirm. Free testosterone is ordered if total is near the limit or if there is obesity, diabetes or another condition that alters SHBG.

What number is "low"?

The harmonized range for healthy men aged 19 to 39 is 264 to 916 ng/dL. The large trials used 275 or 300 ng/dL as their cutoff. Between 264 and 300 is a gray zone completed with free T and SHBG.

How many men truly have low testosterone?

In the European study of 3,369 men aged 40 to 79, 2.1% had sexual symptoms plus confirmed low hormone levels. At 40 it was 0.1% and at 70, 5.1%.

Does treatment give you energy?

In the largest one-year controlled trial, no: vitality did not improve versus placebo. Sexual function (moderate) and mood (slight) did improve.

Does testosterone harm the heart?

TRAVERSE (5,246 at-risk men) found no increase in heart attacks or strokes. It did find more atrial fibrillation, pulmonary embolism, acute kidney injury and fractures.

Does losing weight raise testosterone?

Yes. A meta-analysis of 24 studies found a rise of about 83 ng/dL with diet and about 250 ng/dL with bariatric surgery, with no hormone therapy. The more weight lost, the larger the rise.

Which labs are ordered for this?

A clinician decides. Once you start your program, a licensed physician reviews your case and orders labs only if they consider it necessary. Eligibility is determined by medical evaluation.

Do you offer care in Spanish?

Yes. All our content and care are available in Spanish and English.

Sources

• Wu FC, Tajar A, Beynon JM, et al. Identification of late-onset hypogonadism in middle-aged and elderly men (EMAS). N Engl J Med. 2010;363:123-135. DOI · via PubMed
• Bhasin S, Brito JP, Cunningham GR, et al. Testosterone therapy in men with hypogonadism: an Endocrine Society clinical practice guideline. J Clin Endocrinol Metab. 2018;103:1715-1744. DOI · via PubMed
• Travison TG, Vesper HW, Orwoll E, et al. Harmonized reference ranges for circulating testosterone levels in men of four cohort studies in the United States and Europe. J Clin Endocrinol Metab. 2017;102:1161-1173. DOI · via PubMed
• Hall SA, Esche GR, Araujo AB, et al. Correlates of low testosterone and symptomatic androgen deficiency in a population-based sample (BACH). J Clin Endocrinol Metab. 2008;93:3870-3877. DOI · via PubMed
• Snyder PJ, Bhasin S, Cunningham GR, et al. Effects of testosterone treatment in older men (Testosterone Trials). N Engl J Med. 2016;374:611-624. DOI · via PubMed
• Lincoff AM, Bhasin S, Flevaris P, et al. Cardiovascular safety of testosterone-replacement therapy (TRAVERSE). N Engl J Med. 2023;389:107-117. DOI · via PubMed
• Snyder PJ, Bauer DC, Ellenberg SS, et al. Testosterone treatment and fractures in men with hypogonadism (TRAVERSE). N Engl J Med. 2024;390:203-211. DOI · via PubMed
• Corona G, Rastrelli G, Monami M, et al. Body weight loss reverts obesity-associated hypogonadotropic hypogonadism: a systematic review and meta-analysis. Eur J Endocrinol. 2013;168:829-843. DOI · via PubMed
• Corona G, Giagulli VA, Maseroli E, et al. Testosterone supplementation and body composition: results from a meta-analysis of observational studies. J Endocrinol Invest. 2016;39:967-981. DOI · via PubMed
• Gregorič N, Šikonja J, Janež A, Jensterle M. Semaglutide improved sperm morphology in obese men with type 2 diabetes mellitus and functional hypogonadism. Diabetes Obes Metab. 2025;27:519-528. DOI · via PubMed
• U.S. Food and Drug Administration. FDA issues class-wide labeling changes for testosterone products. February 28, 2025. FDA

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This article is informational and is not medical advice. SCTS1 does not prescribe medication. All medical care, prescriptions, and treatment plans are provided by licensed healthcare providers through our partner platform. Treatment eligibility is determined by a licensed provider. Compounded medications contain the same active ingredient class but are not FDA-approved finished pharmaceuticals. Individual results vary and are not guaranteed.