Low testosterone causes fall into two groups: a problem in the testicles themselves (primary hypogonadism) or weak signals from the pituitary or hypothalamus in the brain (secondary hypogonadism).
Obesity, diabetes, opioid medicines, sleep apnea and serious illness are common contributors.
This guide explains both types of hypogonadism, the medicines and health conditions that can lower testosterone, and the blood tests a physician uses to find the cause.
| Category | Where the problem sits | Typical LH and FSH | Examples |
|---|---|---|---|
| Primary | Testicles | Elevated | Genetic conditions, injury, infection, torsion, cancer treatment |
| Secondary | Hypothalamus or pituitary | Low or inappropriately normal | Pituitary tumors, high prolactin, head injury, iron overload |
| Medication-related | Feedback and signaling | Suppressed | Opioids, glucocorticoids, outside androgens |
| Functional | An axis dampened by another condition | Often low or normal | Obesity, sleep disruption, acute illness, energy deficit |
In this article
Why the Cause of Low Testosterone Matters
Two men with the same low result can need very different care. A pituitary problem may call for imaging and other hormone tests, while low testosterone tied to weight, sleep apnea or an opioid medicine may improve when that driver is treated.
The cause also shapes fertility planning and whether testosterone therapy is the right tool at all, which is why the cause is part of the diagnosis rather than an afterthought.
Primary and secondary hypogonadism
What is primary hypogonadism?
Primary hypogonadism means the testicles are not producing enough testosterone despite stimulation from the pituitary. LH and sometimes FSH may be elevated because the brain is trying to drive a response.
Possible causes include genetic conditions, injury, infection, testicular torsion, certain cancer treatments and other damage to testicular tissue. A history of undescended testicles can also be relevant. The timing of the problem affects presentation: causes present before puberty can look different from those acquired in adulthood.
Testicular pain, a new lump, marked asymmetry or sudden swelling needs medical assessment. A testosterone test cannot explain those findings on its own.
What is secondary hypogonadism?
Secondary hypogonadism occurs when the hypothalamus or pituitary does not provide adequate stimulation to otherwise capable testicles. LH and FSH may be low or inappropriately normal in the setting of low testosterone.
Causes can include pituitary tumors, elevated prolactin, prior pituitary surgery or radiation, head injury, genetic conditions, iron overload and some medicines. Severe or persistent headache, visual change or other neurological symptoms can affect how urgently a pituitary cause is investigated.
If testosterone is clearly low, LH would normally rise in response. An LH value inside the printed range can therefore still need investigation.
Medicines, obesity and diabetes
Which medicines can lower testosterone?
Opioids can suppress hypothalamic and pituitary signaling. Glucocorticoids can also affect the axis, particularly with substantial or prolonged exposure. Other medicines may influence prolactin, hormone metabolism or testicular function depending on the product and clinical setting.
Performance-enhancing androgen products and externally supplied testosterone can suppress LH and FSH through feedback. That suppression can reduce the body’s own testosterone production and sperm production. Recovery after stopping is variable and should not be predicted from an online timeline.
A medicine should not be stopped merely because it appears on a general list. The reason it was prescribed, dose, duration and available alternatives matter. The prescribing clinician should manage any change, especially when abrupt withdrawal creates risk.
How do obesity, diabetes and metabolic health relate?
Higher body fat is associated with lower total testosterone in many men. Changes in sex hormone-binding globulin, insulin resistance, inflammation and disruption of the hormonal axis can all contribute. The relationship can run in more than one direction and differs among individuals.
Type 2 diabetes and metabolic syndrome are also associated with low testosterone, but association is not the same as an automatic diagnosis. A man with diabetes still needs compatible symptoms and reliable testing. Likewise, a low value does not prove that body weight is the only cause.
Substantial weight change can alter hormone measurements and symptoms. A clinician may consider whether treating sleep, nutrition, activity or metabolic disease changes the picture before attributing every concern to lasting gland failure.
Sleep apnea, illness and low energy intake
Can sleep problems lower testosterone?
Testosterone follows a daily rhythm and is connected to sleep. Short, fragmented or poorly timed sleep can affect morning levels. Obstructive sleep apnea is common in men with obesity and may coexist with low testosterone symptoms such as fatigue, reduced concentration and lower sexual function.
Those overlapping symptoms create a diagnostic trap. Treating a hormone number without asking about loud snoring, witnessed breathing pauses, daytime sleepiness or shift work can miss a major contributor.
Acute sleep loss before a blood draw can add noise, but one imperfect night does not establish a cause. The clinician looks for a persistent sleep pattern, symptoms and repeat hormone results obtained under suitable conditions.
Do illness, undernutrition and overtraining matter?
Acute illness can temporarily suppress testosterone. Major surgery, systemic inflammation and severe chronic disease can also affect the axis. Testing during a period of significant illness may not reflect a person’s stable baseline.
Energy deficit matters too. Severe calorie restriction, very low energy availability and excessive training without recovery can disrupt reproductive hormone signals. These contexts are different from ordinary exercise or a balanced weight-management plan.
Nutrition-related suppression should be evaluated rather than answered with a branded supplement. Restoring adequate intake may be relevant when a true deficit exists, but vitamins or so-called testosterone boosters do not correct every pituitary, testicular or medical cause.
Blood tests that help find the cause
How is the cause investigated?
Evaluation begins by confirming the pattern. Morning total testosterone is usually repeated because levels vary by time, sleep, food intake, illness and laboratory method. Free testosterone or sex hormone-binding globulin may add context in selected cases.
Symptoms and reproductive goals matter. The history usually covers:
- Sexual function, fertility and puberty
- Testicular history
- Medicines, substance use and prior hormone use
- Sleep, weight change, illness and surgery
Examination may identify testicular, body-hair or other findings that guide testing.
LH and FSH help separate primary from secondary patterns. Prolactin, iron studies, thyroid testing or pituitary imaging follow when the history and initial results support them, not as a universal package.
The detailed guide on how low testosterone is diagnosed explains confirmation and follow-up. Diagnosis comes before any treatment discussion. Through Atlas HRT, an independent Florida-licensed physician reviews the confirmed pattern and its likely cause, then decides whether testosterone cypionate injection, enclomiphene or a different path fits.
We think the question “why is it low?” deserves as much attention as “how low is it?”. Treating the number without looking for the cause can miss something fixable, like an opioid side effect or untreated sleep apnea, and occasionally something serious, like a pituitary problem.
Common questions
Can stress lower testosterone?
Severe or persistent stress can interact with sleep, illness, nutrition and the hormonal axis. Stress is not specific enough to explain a confirmed low pattern without considering other causes.
Can opioid medicines cause low testosterone?
Yes. Opioids can suppress hypothalamic and pituitary signaling. Risk depends on the medicine and exposure, and any change should be managed by the prescribing clinician.
Does obesity always cause low testosterone?
No. Obesity is associated with lower testosterone through several pathways, but it is not the only cause and does not establish hypogonadism on its own.
Atlas HRT Team
Reviewed by · Last reviewed September 2026Atlas HRT specializes in low testosterone testing and treatment for men in Florida.
Sources
- Male hypogonadism, MedlinePlus
- FDA testosterone information for patients and providers, U.S. Food and Drug Administration
