Causes
Physicians divide causes into problems with the testicles themselves (primary hypogonadism) and problems with the brain's hormonal signals (secondary hypogonadism):- Primary causes: Testicular injury, mumps infection of the testicles, chemotherapy or radiation, and genetic conditions such as Klinefelter syndrome.
- Secondary causes: Disorders of the pituitary gland or hypothalamus, significant obesity, and untreated sleep apnea can all suppress the signals that drive testosterone production.
- Chronic illness: Poorly controlled diabetes, liver or kidney disease, and other long-term conditions commonly lower testosterone.
- Medications: Long-term opioid painkillers and corticosteroids are frequent, and often overlooked, causes.
- Alcohol and anabolic steroids: Heavy long-term drinking and the use of anabolic steroids or performance supplements both suppress the body's own testosterone production, sometimes for months after they are stopped.
Symptoms
Symptoms develop gradually and are easy to attribute to "just getting older":- Sexual changes: Reduced sex drive, fewer spontaneous erections, and erectile difficulty.
- Energy and mood: Persistent fatigue, low motivation, irritability, difficulty concentrating, and symptoms that can resemble depression.
- Body composition: Loss of muscle mass and strength, increased body fat, and sometimes breast tissue enlargement.
- Bone health: Testosterone helps maintain bone density, so long-standing deficiency contributes to osteoporosis and fracture risk in men.
- Other physical changes: Reduced body and facial hair, hot flashes or sweats, and in some men smaller or softer testicles.
- Blood counts and sleep: Testosterone supports red blood cell production, so long-standing deficiency can contribute to mild anemia, and poor sleep quality is a common companion complaint.
Diagnosis
Because testosterone levels swing during the day and drop temporarily with illness or poor sleep, diagnosis requires a low result on at least two separate morning blood tests, drawn when you are otherwise well. Symptoms alone are not enough to make the diagnosis, and a single borderline value should never lead straight to lifelong therapy. Your physician will also examine you and review your complete medication and health history, since a correctable cause is often hiding there. When the total testosterone is borderline - or when obesity, thyroid disease, or liver disease changes the level of the protein that carries testosterone through the blood - a free testosterone level gives a clearer picture. If levels are confirmed low, additional tests such as LH, FSH, and prolactin help determine whether the problem starts in the testicles or the pituitary, which guides treatment. A pituitary MRI or a bone density scan is added when the pattern of results points that way.Treatment
Treatment is individualized, and not every man with a borderline number needs medication:- Treat the underlying cause: Weight loss, better sleep, treating sleep apnea, improving diabetes control, and reviewing medications can restore levels naturally in some men.
- Testosterone replacement therapy: Options include injections such as testosterone cypionate, daily gels, and patches. Therapy requires periodic monitoring of testosterone levels, blood counts, and prostate health (PSA).
- Fertility considerations: Testosterone replacement suppresses sperm production. Men who want to father children may instead be treated with medications such as clomiphene, which stimulate the body's own testosterone production.
Monitoring and Safety
Testosterone replacement is a long-term commitment that calls for regular follow-up rather than a prescription and a handshake:- Blood counts: Therapy can raise the red blood cell count and thicken the blood, so a periodic blood count is standard and the dose is adjusted if the count climbs.
- Prostate health: A PSA level and a review of urinary symptoms are obtained before starting and rechecked during treatment.
- Side effects to report: Acne or oily skin, fluid retention and ankle swelling, breast tenderness, mood swings, and worsening snoring or sleep apnea are all reasons to call your physician.
- Gel precautions: Topical testosterone can transfer to a partner or child through skin contact, so the application site should be covered and washed before close contact.
What Testosterone Treatment Is Like
The page above covers when low testosterone is real. This section covers what happens after that: what improves and when, the trade-offs between forms, the safety questions men ask most, and the conditions that masquerade as it.
What improves, and how quickly
Sex drive and energy usually respond within several weeks, mood and concentration over one to three months, and muscle mass and body fat over three to six months with exercise; bone density takes a year or more. If nothing meaningful has changed after six months at a normal level, the symptoms had another cause and treatment is stopped rather than escalated. Erections improve less reliably than desire; erectile dysfunction often still needs tadalafil or similar treatment.
Injections versus gels
Testosterone cypionate injections are inexpensive and reliable, but a dose every two weeks produces a peak and a trough that some men feel as mood and energy swings; smaller weekly doses smooth that out. Daily gels give steadier levels but must be covered and washed off before contact with a partner or child. Levels are checked midway between injections or after a gel dose, targeting the middle of the normal range, not the top.
The safety questions
A large trial reported in 2023 found no increase in heart attacks or strokes in older men with confirmed low testosterone, which settled the biggest concern, though it found somewhat more atrial fibrillation and blood clots in the lungs. Thickened blood is the most common problem and is handled by lowering the dose or spacing injections. Treatment can worsen sleep apnea, which is screened for first. Testosterone from a clinic that does not check blood counts and PSA is not safe, and gym anabolic steroids or "boosters" suppress the body's own production for months.
Reversible causes and the conditions confused with it
Weight loss, treated sleep apnea, and stopping opioids can raise testosterone enough that replacement is unnecessary. Depression, hypothyroidism, and anemia produce the same fatigue and low drive, and hemochromatosis lowers testosterone directly by depositing iron in the pituitary, so those are checked first. Our when to test and treat article covers the decision.
Fertility, bones, and the long view
Men who may want children are treated with clomiphene rather than testosterone, since replacement shuts down sperm production. Long-standing deficiency is a reason for a bone density scan, since osteoporosis in men is underdiagnosed; our men's bone health article explains. Our endocrine team manages testing and monitoring. The Endocrine Society and the MedlinePlus publish patient guidance.
If you started testosterone without two morning blood tests, or have been on it a year without a blood count, schedule a visit.