How unsupervised testosterone use can affect fertility—and what a new, still preliminary analysis suggests about male hormone levels over the past 50 years.


Key point: The widely reported 54% decline comes from an analysis presented at a scientific conference. It has not yet been published as a complete, peer-reviewed paper. The result deserves attention, but it is not definitive proof.


Testosterone has become one of social media’s latest obsessions.

Fitness influencers, podcasters and content creators increasingly present testosterone replacement therapy, or TRT, as a shortcut to greater strength, energy, confidence, muscle growth and sexual performance. In some videos, young men display testosterone injections or gels as casually as they might show a daily supplement.

The message is simple and persuasive: if you feel tired, unmotivated or dissatisfied with your performance, low testosterone is probably the reason.

The medical reality is far more complex.

Exogenous testosterone is not a vitamin or a harmless performance enhancer. It is a prescription treatment intended for selected men with properly diagnosed hypogonadism. Its use requires an accurate diagnosis, an assessment of potential risks and ongoing clinical monitoring.

For men who want children, starting testosterone without appropriate medical guidance can also produce the opposite of the desired result.


How testosterone can reduce sperm production


Testosterone and sperm production are regulated by the hypothalamic–pituitary–gonadal axis, a signalling system connecting the brain, pituitary gland and testes.

The hypothalamus releases gonadotropin-releasing hormone, which prompts the pituitary to produce luteinising hormone and follicle-stimulating hormone. These signals support testosterone production inside the testes and the development of sperm.

When testosterone is supplied from an external source, the brain detects that circulating levels are already adequate. Through negative feedback, it may reduce the hormonal signals sent to the testes. Blood testosterone can therefore rise while the very high concentration of testosterone required inside the testes falls.

The result may be a substantial reduction in sperm count. Some men develop oligospermia, while others may develop temporary azoospermia, meaning that no sperm are detected in the ejaculate.

This is why the AUA/ASRM male infertility guideline states that testosterone monotherapy should not be prescribed to men who are interested in current or future fertility. The Endocrine Society guideline likewise recommends against starting testosterone therapy in men planning fertility in the near term.

TRT should not be regarded as a dependable male contraceptive. The degree of sperm suppression varies, so it cannot reliably prevent pregnancy. It can, however, become a serious and unintended obstacle to conception.


Does fertility return after testosterone is stopped?


Sperm production recovers in many men after exogenous testosterone is discontinued, but recovery is neither immediate nor identical for everyone.

It may take several months and, in some cases, a year or longer. Evidence on recovery comes partly from hormonal contraceptive studies and partly from observational data involving TRT or anabolic-androgenic steroid use, so no single timetable applies to every patient. Age, duration and dose of exposure, baseline testicular function and other health factors may all affect recovery. A clinical review of spermatogenic recovery notes that the process can take months and occasionally years.

No one should therefore assume that fertility will return as soon as testosterone is stopped. A man who wants children now or may want them later should discuss this before beginning any hormonal treatment. Depending on the situation, assessment by an andrologist, urologist or endocrinologist—and sometimes a semen analysis—may be appropriate.


When is testosterone genuinely low?


Fatigue, low mood, poor concentration, reduced sexual desire and difficulty building muscle do not, by themselves, establish testosterone deficiency.

The same symptoms may occur with chronic stress, insufficient sleep, depression, obesity, excessive training, restrictive dieting, sleep apnoea, chronic illness or the use of medicines such as opioids and corticosteroids.

In a 2026 statement on testosterone replacement therapy, the Endocrine Society emphasises that symptoms alone are not diagnostic. A proper diagnosis requires compatible signs or symptoms together with consistently low testosterone measured accurately on at least two separate early-morning, fasting tests. Further investigation may be needed to determine whether the cause lies in the testes, pituitary, hypothalamus, medication use or a potentially reversible health condition.

Timing matters because testosterone varies during the day and is generally highest in the morning. Laboratory method matters too: different assays can produce meaningfully different results, which is another reason a single random test should not be used to justify lifelong treatment.

Testosterone also tends to decrease with age, but there is no universal point at which every man undergoes a sudden transition equivalent to menopause. The term “andropause” may therefore be misleading. Menopause is a defined biological transition; age-related testosterone changes in men are usually gradual, highly variable and strongly influenced by health, medication and body composition.


The striking 54% figure—and why it needs caution


A new analysis presented in July 2026 at the 42nd Annual Meeting of the European Society of Human Reproduction and Embryology in London brought the subject back into the headlines.

According to reporting on the conference presentation, the researchers combined six longitudinal studies involving 118,593 men from Israel, the United States, Brazil, Finland and Denmark. The data covered the period from 1972 to 2019. The pooled result suggested that mean total testosterone levels fell by approximately 54%, equivalent to more than 1% per year, with the decline apparently accelerating after 2000.

That is a striking finding, but it must be interpreted carefully.

The analysis was presented at a conference and, at the time of writing, had not been published as a complete paper that had undergone independent peer review. The individual studies accounted for age, but obesity—closely associated with lower testosterone—was not controlled for in the pooled analysis, according to The Guardian’s report on the presentation.

Until the full methods and results are published, it is also difficult to assess fully the effects of differences in study populations, blood-sampling conditions, laboratory assays and other sources of confounding.

The correct interpretation is therefore not that science has proved testosterone has fallen by exactly 54% in all men worldwide. The analysis suggests a potentially important long-term trend that deserves rigorous investigation. The number is a serious signal, not a final answer.


What might be contributing to lower testosterone levels?


There is unlikely to be a single explanation.

Obesity is one of the leading candidates. Excess body fat can alter hormonal signalling and metabolism, and obesity is strongly associated with lower circulating testosterone. Type 2 diabetes and insulin resistance are also linked with hormonal changes. For men whose low testosterone is associated with overweight or obesity and no other identified cause, the Endocrine Society’s 2026 statement describes weight loss as the usual first-line approach.

Sleep disorders, chronic illness, certain medications, severe psychological stress and poor metabolic health may also lower testosterone in individual men. These factors can help explain a low result, although they do not by themselves prove the cause of a population-wide historical trend.

Researchers are also studying air pollution and endocrine-disrupting chemicals found in some plastics, pesticides, cosmetics and household products. These exposures are biologically plausible concerns, but their contribution to the reported long-term decline has not been established conclusively. Current evidence is inconsistent, and the full explanation may involve a combination of metabolic, environmental, medical and behavioural factors.


Testosterone is not a measure of masculinity


One of the most damaging social-media messages is that a testosterone result determines how strong, successful or masculine a man is.

Testosterone is an important hormone, not a masculinity score.

It contributes to sexual function, muscle mass, bone density, red blood cell production, sperm production and several aspects of physical health. It does not determine a person’s character, confidence or social value.

Turning a medical therapy into a lifestyle product creates a real risk: healthy men may begin hormonal treatment without an appropriate diagnosis, without adequate monitoring and without understanding the possible effect on fertility.


What should a concerned man do?


If symptoms persist, the first step is not to buy a “testosterone booster” or copy a dosage from a social-media video.

The appropriate next step is a medical assessment, correctly timed blood tests and an investigation of possible causes. A man should mention at the outset whether he wants children now or may want them in the future.

Testosterone replacement can be useful and effective for appropriately selected men with confirmed hypogonadism. That does not make it suitable for everyone.

The problem is not testosterone itself. The problem is using it without a diagnosis, without clinical supervision and according to an image of masculinity designed for social-media engagement.

This article is for general information and does not replace personalised medical advice, diagnosis or treatment.

Evidence note: Confidence is high that exogenous testosterone can suppress sperm production. Confidence in the exact size of the reported long-term decline is limited because the 54% estimate currently comes from a conference presentation rather than a complete peer-reviewed publication. https://healthpont.com/testosterone-and-male-fertility/