Male hypogonadism is a condition in which the body doesn’t produce enough testosterone, the hormone that drives male sexual development, muscle maintenance, bone strength, and red blood cell production. It’s diagnosed when total testosterone falls below 300 ng/dL on two separate morning blood draws. Hypogonadism can begin before birth, during puberty, or later in adulthood, and the symptoms vary depending on when it starts.
Primary vs. Secondary Hypogonadism
There are two distinct types, and the difference comes down to where the problem originates. Primary hypogonadism means the testicles themselves aren’t functioning properly. They receive the right chemical signals from the brain but can’t produce enough testosterone in response. One well-known cause is Klinefelter syndrome, a genetic condition where a male is born with an extra X chromosome. Other causes include undescended testicles, physical injury to the testicles, mumps infection affecting the testes, and certain cancer treatments like chemotherapy or radiation.
Secondary hypogonadism starts further upstream. The testicles are capable of making testosterone, but the brain’s signaling system isn’t telling them to. The pituitary gland and a nearby brain region called the hypothalamus normally send hormonal signals that trigger testosterone production. When something disrupts that chain, testosterone drops. Pituitary tumors, head injuries, and inflammatory diseases can all interfere. So can certain medications, particularly opioid painkillers and some hormonal drugs. Obesity is another significant contributor, as excess body fat disrupts the hormonal signaling loop.
Doctors distinguish between the two types through blood work. In primary hypogonadism, the brain’s signaling hormones are elevated because the brain is essentially shouting louder at testicles that can’t respond. In secondary hypogonadism, those signaling hormones are normal or low, pointing to a problem with the brain’s instructions rather than the testicles themselves.
Symptoms Before and After Puberty
When hypogonadism develops before puberty and goes untreated, the signs are tied to delayed development: sparse body hair, delayed growth plate closure in bones, and incomplete genital development. The voice may not deepen, and muscle mass doesn’t fill in the way it typically would during adolescence.
When testosterone drops after puberty, the symptoms are different and often more subtle. The most common complaints that prompt testing are reduced sex drive, erectile difficulty, and persistent fatigue. But the effects reach well beyond sexual function. Men often notice decreased energy and stamina, depressed mood, increased irritability, and difficulty concentrating. Physical changes include loss of muscle mass, increased belly fat, and reduced bone density, which raises the risk of osteoporosis and fractures. Some men experience hot flushes similar to what women describe during menopause. Anemia (low red blood cell count) is also common, since testosterone plays a role in stimulating red blood cell production.
How It’s Diagnosed
Diagnosis requires at least two blood tests showing total testosterone below 300 ng/dL. European guidelines use a slightly higher cutoff of about 350 ng/dL. The timing of the blood draw matters because testosterone levels naturally peak in the early morning and drop throughout the day. For men under 45, blood should be drawn before 9 AM. For men 45 and older, this daily variation flattens out, so testing before 2 PM is acceptable.
Repeat testing is essential. Up to 30% of men who test low on their first morning draw will have a normal result when tested again. A single low reading is not enough for a diagnosis. If both tests confirm low levels, additional blood work helps determine whether the cause is primary or secondary, which guides treatment decisions.
Treatment With Testosterone Replacement
Testosterone replacement therapy (TRT) is the standard treatment when symptoms are present alongside confirmed low levels. It comes in several forms, each with trade-offs.
- Topical gels are applied daily to the skin. About 74 to 87% of men reach normal testosterone levels with gels. The main drawback is the risk of transferring testosterone to women or children through skin contact, which can cause hormonal side effects in them. Skin irritation at the application site is also common.
- Skin patches are worn and replaced every 24 to 48 hours. They’re effective, with over 85% of men reaching levels above 300 ng/dL, but up to 60% of users experience skin reactions like itching or redness at the patch site.
- Injections are given every one to two weeks and produce higher peak testosterone levels than other methods. They’re cost-effective but create more of a rollercoaster pattern, with levels spiking after injection and dropping before the next one.
- Nasal gels are applied inside the nose three times daily. In clinical testing, 90% of men achieved normal levels. They avoid the skin-transfer risk of topical gels but can cause nasal irritation, nosebleeds, and sinus symptoms.
- Oral tablets absorbed through the gum lining bypass the liver, which historically made oral testosterone problematic. They restore levels to a normal range but can cause gum tenderness, nausea, and mild increases in blood pressure.
Cardiovascular Safety of TRT
For years, conflicting data raised concerns about whether testosterone therapy increased heart attack and stroke risk. In 2015, the FDA required manufacturers to conduct rigorous clinical trials to settle the question. The largest of these, known as the TRAVERSE trial, enrolled over 5,000 men with hypogonadism who either had existing cardiovascular disease or multiple risk factors for it. Over an average follow-up of 22 months, the rate of major cardiac events (cardiovascular death, heart attack, or stroke) was nearly identical: 7.0% in the testosterone group versus 7.3% in the placebo group.
That said, the trial did find some notable differences. Men on testosterone had higher rates of atrial fibrillation (3.5% vs. 2.4%), acute kidney injury (2.3% vs. 1.5%), and pulmonary embolism compared to placebo. So while TRT doesn’t appear to increase the risk of heart attack or stroke, it’s not entirely without cardiovascular effects.
TRT and Fertility
This is one of the most important things to understand before starting treatment: testosterone replacement therapy suppresses sperm production. It does this by telling the brain that there’s already plenty of testosterone circulating, which shuts down the hormonal signals the testicles need to make sperm. For men who want to have children, this is a serious concern.
Alternative treatments exist that can raise testosterone while preserving fertility. These work by stimulating the body’s own testosterone production rather than replacing it from outside. Your doctor can discuss these options if fertility is relevant to you, and it’s critical to raise this before starting any form of TRT, not after.
What Gets Monitored During Treatment
Once on TRT, regular blood work tracks both effectiveness and safety. The two most important markers are hematocrit (the percentage of red blood cells in your blood) and, for men over 40, PSA (a protein related to prostate health).
Testosterone stimulates red blood cell production, which is helpful when you’re anemic but problematic if levels climb too high. Before starting treatment, hematocrit should be below 50%. Once on therapy, it’s checked every 6 to 12 months with the goal of keeping it below 54%, because excessively thick blood raises the risk of blood clots. PSA monitoring follows standard prostate cancer screening guidelines, though doctors may test more frequently in men with a history of prostate cancer.