What it is
Testosterone is the main male sex hormone, made mostly in the testes. Hypogonadism means the body makes too little of it, with symptoms. Low testosterone alone isn't enough for a diagnosis.[1]
The pituitary gland signals the testes (Leydig cells) to make testosterone. Problems can start in the testes (primary) or in the pituitary or brain (secondary).[1] Testosterone declines by roughly 1% a year after age 30, but does not normally fall to very low levels even in old age.[1]
The Endocrine Society's guideline recommends diagnosing hypogonadism only in men with consistent symptoms and signs plus unequivocally and consistently low serum testosterone, confirmed by repeat fasting morning measurements; free testosterone is considered when total levels are borderline or SHBG is altered.[2]
See the testes, where most testosterone is made — and the pituitary gland that controls them.
See it in 3DHow common it is
What happens with age
Testosterone declines slowly with age, but the Endocrine Society notes it is not approved to treat ageing itself, or to boost strength, athletic performance or appearance.[1]
Causes and risk factors
Things you can't change
- Testicular injury or infection, past radiation or chemotherapy.[1]
- Pituitary or brain disorders, and genetic conditions such as Klinefelter syndrome.[1]
Things you can change
Symptoms worth reporting to a doctor
- Lower sex drive and erection problems
- Low sperm count or infertility
- Low energy, low mood or irritability
- Less muscle, breast enlargement or tenderness, hot flashes
- Over time: body hair loss and weaker bones
Many of these have other causes too, which is why proper testing matters.[1]
How it's diagnosed
Types of treatment
- Treating reversible causes first. For example, weight loss in men with obesity.[1]
- Testosterone therapy. Injections, gels, patches, tablets, pellets or nasal gel for men with consistently low levels and symptoms. Risks include lower sperm production, a high red blood cell count, acne and prostate enlargement.[1]
Testosterone is not advised for men planning to have children, men with prostate or breast cancer, men with urinary problems from an enlarged prostate, untreated sleep apnoea, a high red blood cell count, or a heart attack or stroke in the past 6 months.[1] Your care team decides with you.
What you can do
Weight and activity first
Obesity is a reversible cause; weight loss is the first step for many men.[1]
Questions to ask your doctor
- Were my testosterone tests done in the morning, and repeated?
- What could be causing my low level?
- Would weight loss or changing a medicine help first?
- What are the risks of testosterone for me, and how will they be monitored?
- How will treatment affect my fertility?
Myth vs. fact
Related topics
Erectile dysfunction (ED)
Trouble getting or keeping an erection is common and treatable — and it can be an early clue to heart and blood-vessel problems worth checking.
Testicular cancer
A cancer of younger men — the average age at diagnosis is about 33. It's uncommon and usually very treatable. Know what's normal for you.
Type 2 diabetes and prediabetes
Blood sugar that stays too high. Millions have it without knowing — and prediabetes can often be stopped from progressing.
Sources
- Endocrine Society. Hypogonadism in Men (patient resource). Checked 23 October 2026.
- Bhasin S, et al. J Clin Endocrinol Metab 2018;103(5):1715–1744. Testosterone Therapy in Men With Hypogonadism: An Endocrine Society Clinical Practice Guideline. Checked 23 October 2026.
The owner of this website is not a doctor. Human Atlas provides educational anatomy information and does not diagnose, stage, or treat disease. Talk to a qualified clinician about anything concerning your own health.