You should start testosterone therapy only after blood tests on two separate mornings confirm your levels are consistently low and you have symptoms that match. There’s no single age or number that automatically makes someone a candidate. The decision depends on your test results, your symptoms, whether you’ve ruled out reversible causes, and your personal health profile.
What Counts as Low Testosterone
The American Urological Association defines low testosterone as a total level below 300 ng/dL in adult males without obesity. Healthy levels typically fall between 450 and 600 ng/dL. But a single blood draw isn’t enough to confirm a problem. Testosterone fluctuates significantly from day to day and even hour to hour, so the standard diagnostic process requires two separate morning blood draws, taken while fasting, between 7 and 10 a.m. That’s the window when your levels peak. Eating before the test or drawing blood later in the day can artificially push your numbers down.
If your total testosterone is borderline (near 300 ng/dL), your doctor may also check your free testosterone, which is the portion actually available for your body to use. Certain conditions, including obesity, thyroid disorders, and aging, can shift the protein that binds testosterone in your blood, making total levels a less reliable picture on their own.
Symptoms That Point to Deficiency
Low numbers alone aren’t enough. The Endocrine Society recommends diagnosing testosterone deficiency only in men who have both consistently low levels and symptoms. Common symptoms include reduced sex drive, erectile difficulty, persistent fatigue, loss of muscle mass, increased body fat (especially around the midsection), depressed mood, and difficulty concentrating. Some men also notice decreased bone density or hot flashes.
These symptoms overlap heavily with other conditions like depression, sleep apnea, thyroid problems, and simple aging. That overlap is exactly why screening questionnaires aren’t reliable on their own. The most widely used one, the Androgen Deficiency in the Aging Male (ADAM) questionnaire, catches about 90% of men who actually have low testosterone, but it also flags a large number of men who don’t. Its specificity is only around 41%, meaning it produces many false positives. Blood work is the only way to confirm the diagnosis.
Age and the Natural Decline
Testosterone drops about 1% per year after age 30. That’s a normal biological process, not a disease. By age 60 or 70, many men have levels that would have been considered low at age 25, yet they feel fine. The question isn’t whether your testosterone is lower than it used to be. It’s whether it’s low enough, combined with symptoms, to justify treatment.
There’s no minimum or maximum age for starting therapy. Younger men with a pituitary disorder or testicular injury can develop deficiency in their 20s or 30s. Older men may have levels well below 300 ng/dL but attribute their symptoms to aging without ever getting tested. If your symptoms are affecting your quality of life and your levels come back low on two separate tests, age alone shouldn’t determine whether you’re a candidate.
Rule Out Reversible Causes First
Before committing to what may be a lifelong treatment, it’s worth investigating whether something fixable is driving your levels down. Acute illness, high stress, poor sleep, and certain medications (particularly opioids) can temporarily suppress testosterone. The Endocrine Society specifically recommends against testing during or shortly after an acute illness, because results won’t reflect your baseline.
Obesity is one of the most significant reversible factors. Excess body fat increases the conversion of testosterone to estrogen and can lower total and free testosterone substantially. Weight loss alone can raise levels enough that some men no longer meet the threshold for deficiency. Sleep apnea is another common culprit. Treating it with a CPAP machine can improve testosterone production without any hormonal intervention. If either of these applies to you, addressing them first gives you a clearer picture of where your testosterone actually sits when your body isn’t working against itself.
Fertility Is a Major Timing Factor
This is the single most important consideration for younger men. Testosterone therapy suppresses your body’s natural sperm production, and the effect can be dramatic. About 65% of men with normal sperm counts develop azoospermia (zero detectable sperm) within four months of starting treatment. The Endocrine Society and the American Urological Association both recommend against testosterone therapy for men who want to have children in the next 6 to 12 months.
The good news is that the effect is usually reversible. Most men return to their baseline sperm counts within 6 to 9 months after stopping therapy. A large analysis found that 90% recovered within 12 months and 100% within 24 months. But “usually reversible” isn’t the same as “guaranteed,” and recovery can take up to two years. If you’re planning a family, bring this up before starting treatment. Alternative medications exist that can raise testosterone while preserving fertility.
Health Conditions That May Rule It Out
Certain conditions make testosterone therapy unsafe or require extra caution. The clearest contraindications are untreated prostate cancer and breast cancer. Testosterone fuels the growth of hormone-sensitive cancers, so men with these diagnoses should not receive it. Men over 40 are typically screened with a PSA (prostate-specific antigen) blood test before starting therapy to rule out undiagnosed prostate cancer.
High-risk individuals need closer evaluation. This includes men with a first-degree relative who had prostate cancer and African American men with a PSA above 3 ng/mL. Sleep apnea is considered a relative contraindication, meaning it doesn’t automatically disqualify you but requires careful management. And if your red blood cell concentration (hematocrit) is already elevated, adding testosterone can push it further, increasing the risk of blood clots.
What Monitoring Looks Like After You Start
Starting testosterone isn’t a one-time decision. It requires ongoing blood work to make sure the therapy is working and isn’t causing problems. The most important safety check is your hematocrit level, which measures how much of your blood is made up of red blood cells. Testosterone stimulates red blood cell production, and if hematocrit rises above 54%, therapy needs to be paused until it drops back down. This is checked at baseline, again at 3 to 6 months, and then annually.
Your doctor will also recheck your testosterone levels to confirm they’ve moved into the target range. PSA screening continues for men over 40. Mood, energy, sexual function, and other symptoms are reassessed to determine whether the therapy is actually helping. If your symptoms don’t improve despite achieving normal testosterone levels, the problem may have been something else entirely.
Cardiovascular Safety
For years, one of the biggest concerns about testosterone therapy was heart risk. A landmark trial published in the New England Journal of Medicine, involving over 5,000 men with hypogonadism who either had cardiovascular disease or were at high risk for it, found that testosterone therapy did not increase the rate of heart attacks, strokes, or other major cardiac events compared to placebo. The event rate was 7.0% in the testosterone group and 7.3% in the placebo group over the study period. This was a reassuring finding, though it applies specifically to men who meet the clinical definition of testosterone deficiency, not to men with normal levels looking for a boost.
The Bottom Line on Timing
The right time to start testosterone therapy is when three things align: your symptoms are affecting your daily life, your blood tests confirm levels consistently below 300 ng/dL on two separate fasting morning draws, and reversible causes have been addressed or ruled out. If you’re planning to have children, the timing shifts. If you have a history of hormone-sensitive cancer, the calculus changes entirely. The decision is personal, but it should always be grounded in confirmed lab results, not just how you feel on a tired Tuesday morning.