What causes low testosterone in young men? The causes that hold up, and the viral ones that don't

“Low T at 25” has become its own genre online: lab screenshots, NoFap streak debates, seed-oil warnings, and a steady stream of advice on what supposedly wrecks a young man’s hormones. Some of it points at real causes. A lot of it does not. This page sorts the explanations by how well they hold up in published research, from national survey data and guideline documents down to the small studies that viral claims tend to rest on, and explains how a doctor actually works out which cause is in play.

What causes low testosterone in young males?

In younger men, the causes with the most published evidence behind them are everyday ones: excess body fat, chronically short sleep, past anabolic steroid use, opioids and heavy drinking. A smaller group has a medical cause, such as Klinefelter syndrome, undescended testicles, mumps orchitis, cancer treatment, or a pituitary problem. Masturbation, soy and occasional cannabis use are not well-supported causes, as covered below.

Two categories help make sense of the list. Doctors split low testosterone into primary causes, where the testes themselves underproduce, and secondary causes, where the brain’s signal to the testes is turned down. A government-hosted clinical reference lists Klinefelter syndrome, undescended testicles, mumps orchitis, hemochromatosis and cancer treatment as primary causes, and pituitary disorders, obesity, HIV, surgery, trauma and stress-induced hypogonadism as secondary ones (Sizar et al., StatPearls, 2024). The split matters because it changes what gets tested next, and whether the cause can be reversed.

Are testosterone levels really falling in young men?

Yes, the trend is real in US survey data, though its cause is not settled. Using the National Health and Nutrition Examination Survey, researchers looked at 4,045 adolescent and young adult men from 1999 to 2016 and found mean total testosterone was lower in the 2011 to 2016 cycles than in 1999 to 2000. Higher body mass index went with lower testosterone, but the decline held even among men with a normal BMI (Lokeshwar et al., Eur Urol Focus, 2021). The authors flag two limits: unmeasured environmental factors, and the fact that different testosterone assays were used across the years.

That finding echoes an older one in middle-aged and older men. In the Massachusetts Male Aging Study, researchers saw a substantial drop in testosterone across calendar time that was independent of age and did not appear to be explained by measured factors such as smoking and obesity (Travison et al., J Clin Endocrinol Metab, 2007). So the honest social-media answer to “why is everyone’s T lower now?” is: partly rising body weight, partly unknown, and nobody has proven the popular single culprits.

Ordinary aging is a slower story. In the same Massachusetts cohort, total testosterone fell about 1.6% per year within individual men aged 40 to 70 at the start (Feldman et al., J Clin Endocrinol Metab, 2002). That pace does not explain a clearly low result in a man in his twenties, which is why a young man with a low reading deserves a look for a specific cause.

The causes of low testosterone, ranked by evidence

The table puts each commonly cited cause next to the strength of the evidence behind it, described in words, and the way it is usually checked. “How it is tested” assumes the low reading has already been confirmed on repeat morning blood tests, as both main guidelines require (AUA guideline; Endocrine Society, 2018).

Causes of low testosterone, the evidence level for each, and how each is usually checked. Sources are cited in the sections below.

Attribute	Evidence level	How it is tested
Excess body fat	Strong: large population studies plus a meta-analysis of weight-loss trials	Weight, total testosterone, LH (often low or normal)
Chronically short sleep	Small experimental study (10 young men)	Sleep history
Past anabolic steroid use	Case-control study of recreational lifters	Honest history, total testosterone, LH and FSH
Regular opioid use	Meta-analysis of observational studies, low overall quality	Medication history, total testosterone
Heavy alcohol use	Review; much of the mechanism work is in animals	Drinking history, total testosterone
Klinefelter syndrome	Established genetic cause; national registry data on how often it is missed	High LH and FSH, then a karyotype (chromosome test)
Pituitary problems, high prolactin	Established medical cause in guidelines	Prolactin when LH is low or low-normal; pituitary MRI in some cases
Undescended testicles, mumps orchitis, cancer treatment	Established medical causes	History, exam, high LH
Masturbation or ejaculation	Myth: small studies show no lasting drop	Not a test target
Soy foods	Myth at the intakes studied: meta-analysis found no effect	Not a test target

Excess body fat

Carrying excess weight is the cause with the most weight of evidence behind it. In the European Male Ageing Study of 3,200 men aged 40 to 79, being overweight or obese went with lower total and free testosterone, and LH stayed unchanged or fell, which the authors read as a problem in the brain’s signal rather than in the testes (Wu et al., J Clin Endocrinol Metab, 2008). The reverse also holds: a meta-analysis of 24 studies found both low-calorie diets and bariatric surgery raised total testosterone, with bigger rises in men who lost more weight and in younger, non-diabetic men (Corona et al., Eur J Endocrinol, 2013). The AUA guideline tells clinicians to counsel every man with low testosterone that losing weight and moving more can raise levels or ease symptoms (AUA guideline).

Chronically short sleep

Sleep is one of the few causes tested experimentally in young men. Ten healthy men, average age about 24, spent three nights with 10 hours in bed and then eight nights with 5 hours. After the restricted week, their daytime testosterone was 10% to 15% lower (Leproult and Van Cauter, JAMA, 2011). It is a small study, so it shows that short sleep can lower levels, not how much it explains across the population. It is also a reason not to test after a run of late nights.

Past anabolic steroid use

This is the cause most specific to gym culture, and it can outlast the cycle by years. A Danish case-control study compared current steroid users, former users who had stopped about 2.5 years earlier on average, and non-using lifters aged 18 to 50. Former users had lower total and free testosterone than controls, 27.2% of them sat below the lower reference limit (no controls did), and they reported more depressive symptoms, erectile dysfunction and low libido (Rasmussen et al., PLoS One, 2016). Current users showed markers of impaired sperm production. A low reading in a man with a steroid history is therefore a different conversation from a low reading with no history, and it is one reason to be candid with whoever orders the labs. For how replacement differs from cycling, see is TRT a steroid.

Opioids and heavy alcohol

Regular opioid use, whether prescribed for pain or not, is linked to lower testosterone in men. A meta-analysis of 17 studies found significantly lower testosterone in men using opioids than in controls, with methadone no different from other opioids, though the authors rated the overall evidence as low quality and the studies as highly varied (Bawor et al., Drug Alcohol Depend, 2015). Alcohol use is associated with low testosterone and affects every level of the hormone system, from the hypothalamus and pituitary to the testes; much of the mechanism evidence in that review comes from animal studies (Emanuele and Emanuele, Alcohol Res Health, 2001).

Medical causes worth ruling out

Some causes are conditions a man is born with or picks up, not habits. Klinefelter syndrome, an extra X chromosome, is the clearest example in younger men. A Danish registry study estimated a prevalence of about 153 per 100,000 males, yet only about a quarter of adult men with it had been diagnosed, and fewer than 10% of expected cases were found before puberty (Bojesen et al., J Clin Endocrinol Metab, 2003). Pituitary problems are the other important group: the AUA guideline calls for a prolactin test when LH is low or low-normal, and a pituitary MRI for men with total testosterone under 150 ng/dL and low or low-normal LH (AUA guideline).

Does masturbation cause low testosterone?

No. The published studies do not show masturbation or ejaculation lowering testosterone in any lasting way. In a German study, ten men had blood drawn continuously during masturbation to orgasm, before and after three weeks of abstinence: orgasm raised prolactin, heart rate and blood pressure, but plasma testosterone was unaltered by orgasm (Exton et al., World J Urol, 2001). The evidence is small and short-term, but none of it points toward depletion.

The details are worth knowing because both sides of the NoFap debate cite the same thin literature:

• Abstinence and a modest rise. The same German study found testosterone was higher after the three-week abstinence period than before it (Exton et al., World J Urol, 2001). That is a change in a group of ten men, not evidence that regular masturbation makes anyone deficient.
• The “day 7 spike.” The specific claim that testosterone peaks on the seventh day without ejaculation matches a small study of 28 men that reported a peak at 145.7% of baseline on day 7 (Jiang et al., J Zhejiang Univ Sci, 2003). PubMed lists that English-language paper as retracted, with a retraction notice issued in 2021, so it should not be cited as settled evidence.
• Right after masturbation. A small randomized cross-over pilot study in young healthy men found that masturbation with a visual stimulus, and the visual stimulus alone, seemed to counteract the normal daytime fall in free testosterone, with no change in hormone ratios; the authors called for larger studies (Isenmann et al., Basic Clin Androl, 2021).

The practical reading: if a young man’s testosterone is genuinely low on repeat morning tests, masturbation is not a credible explanation, and stopping it is not a treatment. The causes in the table above are where a workup looks.

Does soy or cannabis lower testosterone?

Soy does not, at the intakes studied. A meta-analysis of clinical studies in adult men found no significant effect of soy protein or isoflavone intake on total testosterone, free testosterone, SHBG or the free androgen index, whichever statistical model was used (Hamilton-Reeves et al., Fertil Steril, 2010).

Cannabis is genuinely mixed. In 1,577 US men from the 2011 to 2012 national survey, ever-users and never-users had no difference in serum testosterone after adjustment. Men who had used more recently actually had higher levels, a pattern that was stronger in men aged 18 to 29 (Thistle et al., Andrology, 2017). The authors note that an earlier literature had linked marijuana to reduced testosterone, so this is a “not proven either way” rather than a clean bill of health. The Lokeshwar team also raised rising marijuana use as a possible influence on the decline in young men, while calling the question controversial (Lokeshwar et al., Eur Urol Focus, 2021).

How do doctors work out the cause of low testosterone?

They confirm the number first, then use LH and a few targeted tests to find the cause. The AUA guideline uses a total testosterone below 300 ng/dL on two separate early-morning samples, makes the diagnosis only when symptoms or signs are present too, and tells clinicians to measure LH in every man with low testosterone (AUA guideline). The Endocrine Society likewise recommends an evaluation to find the cause once deficiency is confirmed (Endocrine Society, 2018).

What the second round of tests usually points to. Per the AUA guideline and StatPearls.

Attribute	What it suggests	Usual next step
Low testosterone with high LH	Primary: the testes are underproducing	History and exam; a karyotype (chromosome test) in younger men
Low testosterone with low or normal LH	Secondary: the brain’s signal is turned down (for example obesity or a pituitary disorder)	Prolactin; pituitary MRI if testosterone is very low
High FSH	Sperm production is likely impaired	Fertility testing such as a semen analysis

Our guide to blood tests before starting TRT explains each marker, and low testosterone symptoms covers which symptoms point to a real deficiency and which usually have another cause. Because low libido and weaker erections are the most specific symptoms, The Ed Report’s piece on ED and low testosterone is useful context too.

Can low testosterone come back up on its own?

Often it can, when the cause is one of the suppressors rather than damage to the testes or pituitary. Weight loss raised testosterone across the trials in the Corona meta-analysis (Corona et al., Eur J Endocrinol, 2013), and the sleep study produced its drop within a single week of restricted sleep, though it did not test recovery (Leproult and Van Cauter, JAMA, 2011). Recovery is less certain after anabolic steroids: in the Danish study, about a quarter of former users were still below the reference limit years after stopping (Rasmussen et al., PLoS One, 2016). Genetic and pituitary causes are medical problems that need a doctor’s evaluation.

This is also where the supplement aisle comes in. Over-the-counter “boosters” are marketed at exactly this audience, and our review of TRT vs testosterone boosters goes ingredient by ingredient through what the trials found. If a cause is fixable, fixing it comes before any product.

The bottom line

Low testosterone in a young man is a finding that needs an explanation, not a verdict on his habits. The causes with real evidence are mostly ordinary, and several can be reversed: excess body fat, short sleep, opioids, heavy drinking, and, in gym culture specifically, past steroid use. A smaller share are medical conditions that are easy to miss without the right tests. The viral villains fare worse: masturbation does not deplete testosterone in the published data, soy shows no effect, and cannabis is unresolved. Repeat morning bloodwork with LH is what tells the causes apart.

Sources

• Lokeshwar SD, et al. Decline in Serum Testosterone Levels Among Adolescent and Young Adult Men in the USA (Eur Urol Focus, 2021), NHANES 1999 to 2016, 4,045 men; decline persisted at normal BMI; assay and environmental limits: pubmed.ncbi.nlm.nih.gov/32081788
• Travison TG, et al. A population-level decline in serum testosterone levels in American men (J Clin Endocrinol Metab, 2007), age-independent decline not explained by measured factors: pubmed.ncbi.nlm.nih.gov/17062768
• Feldman HA, et al. Age trends in the level of serum testosterone and other hormones in middle-aged men (J Clin Endocrinol Metab, 2002), longitudinal total testosterone decline of 1.6% per year: pubmed.ncbi.nlm.nih.gov/11836290
• Wu FC, et al. Hypothalamic-pituitary-testicular axis disruptions in older men are differentially linked to age and modifiable risk factors: the European Male Aging Study (J Clin Endocrinol Metab, 2008), obesity linked to lower total and free testosterone with unchanged or decreased LH: pubmed.ncbi.nlm.nih.gov/18270261
• Corona G, et al. Body weight loss reverts obesity-associated hypogonadotropic hypogonadism: a systematic review and meta-analysis (Eur J Endocrinol, 2013), diet and bariatric surgery raise testosterone, more with greater weight loss: pubmed.ncbi.nlm.nih.gov/23482592
• Leproult R, Van Cauter E. Effect of 1 Week of Sleep Restriction on Testosterone Levels in Young Healthy Men (JAMA, 2011), 10 men, 5-hour nights, daytime testosterone 10% to 15% lower: pmc.ncbi.nlm.nih.gov/articles/PMC4445839
• Rasmussen JJ, et al. Former Abusers of Anabolic Androgenic Steroids Exhibit Decreased Testosterone Levels and Hypogonadal Symptoms Years after Cessation (PLoS One, 2016), 27.2% of former users below the reference limit: pubmed.ncbi.nlm.nih.gov/27532478
• Bawor M, et al. Testosterone suppression in opioid users: a systematic review and meta-analysis (Drug Alcohol Depend, 2015), lower testosterone in men using opioids; low overall evidence quality: pubmed.ncbi.nlm.nih.gov/25702934
• Emanuele MA, Emanuele N. Alcohol and the Male Reproductive System (Alcohol Research & Health, 2001), alcohol affects all three levels of the hypothalamic-pituitary-gonadal axis and is associated with low testosterone: pmc.ncbi.nlm.nih.gov/articles/PMC6705705
• Bojesen A, et al. Prenatal and postnatal prevalence of Klinefelter syndrome: a national registry study (J Clin Endocrinol Metab, 2003), about 153 per 100,000 males; roughly a quarter of adult cases diagnosed: pubmed.ncbi.nlm.nih.gov/12574191
• Sizar O, Leslie SW, Schwartz J. Male Hypogonadism (StatPearls, NCBI Bookshelf, updated February 2024), primary and secondary causes and the role of LH: ncbi.nlm.nih.gov/books/NBK532933
• American Urological Association. Evaluation and Management of Testosterone Deficiency: AUA Guideline (The Journal of Urology version, PDF), 300 ng/dL on two morning samples, LH, prolactin and MRI rules, FSH and fertility testing, lifestyle counseling: auanet.org Testosterone-Deficiency-JU.pdf
• Bhasin S, et al. Testosterone Therapy in Men With Hypogonadism: An Endocrine Society Clinical Practice Guideline (J Clin Endocrinol Metab, 2018), repeat morning testing and evaluation for the cause: pubmed.ncbi.nlm.nih.gov/29562364
• Exton MS, et al. Endocrine response to masturbation-induced orgasm in healthy men following a 3-week sexual abstinence (World J Urol, 2001), testosterone unaltered by orgasm; higher after abstinence: pubmed.ncbi.nlm.nih.gov/11760788
• Isenmann E, et al. Hormonal response after masturbation in young healthy men: a randomized controlled cross-over pilot study (Basic Clin Androl, 2021), possible effect on free testosterone, no change in hormone ratios: pubmed.ncbi.nlm.nih.gov/34937544
• Jiang M, et al. A research on the relationship between ejaculation and serum testosterone level in men (J Zhejiang Univ Sci, 2003), the day 7 peak claim; listed on PubMed as retracted (2021): pubmed.ncbi.nlm.nih.gov/12659241
• Hamilton-Reeves JM, et al. Clinical studies show no effects of soy protein or isoflavones on reproductive hormones in men: results of a meta-analysis (Fertil Steril, 2010): pubmed.ncbi.nlm.nih.gov/19524224
• Thistle JE, et al. Marijuana use and serum testosterone concentrations among U.S. males (Andrology, 2017), no difference between ever and never users; higher levels with recent use: pubmed.ncbi.nlm.nih.gov/28395129