Testosterone therapy is typically started when two conditions are met: your blood levels are consistently below 300 ng/dL and you have symptoms that match testosterone deficiency. Neither low numbers alone nor symptoms alone are enough. The American Urological Association and the Endocrine Society both require the combination before recommending treatment.
The Blood Level Threshold
The widely accepted cutoff is a total testosterone level below 300 ng/dL, measured on at least two separate morning blood draws. Morning matters because testosterone peaks in the early hours and drops throughout the day; a late-afternoon test can read artificially low. Fasting before the draw is also recommended, since eating can temporarily suppress levels.
Different medical societies around the world use slightly different numbers, ranging from 230 to 350 ng/dL, but 300 ng/dL is the standard in U.S. practice. If your total testosterone falls in a borderline range and your symptoms don’t quite line up, your doctor may also check your free testosterone, the small fraction that circulates unbound to proteins and is biologically active. A free testosterone level below about 65 pg/mL is generally considered supportive evidence of deficiency.
Symptoms That Support a Diagnosis
Low numbers on a lab report aren’t the whole picture. Some men walk around with testosterone below 300 ng/dL and feel fine. Others at the same level are struggling. The symptoms that most reliably track with true testosterone deficiency are sexual: reduced sex drive, fewer morning erections, and difficulty getting or maintaining erections. A large European study of men aged 40 to 79 found that these three sexual symptoms were the strongest predictors of clinically meaningful hypogonadism, more so than fatigue or mood changes.
That said, testosterone deficiency can show up in other ways:
- Physical changes: loss of muscle size and strength, increased body fat, reduced bone density
- Sleep problems: insomnia or poor sleep quality
- Mood and cognition: depression, difficulty concentrating, lower quality of life
- Reproductive: low sperm count
If you’re experiencing several of these alongside confirmed low levels, the case for therapy is stronger.
What Gets Checked Before You Start
Before a prescription is written, your doctor should run through a baseline checklist. This protects you from complications and helps identify whether something else is causing your low levels in the first place.
A hematocrit level (the proportion of red blood cells in your blood) is standard because testosterone can thicken the blood over time. Men over 40 need a PSA test to screen for prostate issues, since testosterone therapy is contraindicated in men with untreated prostate or breast cancer. Your doctor should also check a hormone called LH, which helps distinguish whether the problem originates in the testes or in the brain’s signaling system. If LH is unusually low alongside low testosterone, imaging of the pituitary gland may be needed to rule out a growth like a prolactinoma.
A full cardiovascular history is recommended as well, covering any past heart attacks, strokes, heart failure, or uncontrolled high blood pressure. You’ll also be asked about breast tenderness or enlargement and examined for existing gynecomastia, since testosterone can occasionally worsen breast tissue changes. Men with untreated sleep apnea should know that therapy may aggravate their symptoms, though this is considered a relative rather than absolute contraindication.
Fertility Is a Major Timing Factor
This is one of the most important and most overlooked considerations. Testosterone therapy suppresses sperm production, sometimes severely. If you want to have children now or in the near future, starting standard testosterone replacement is generally a poor idea.
For men hoping to conceive within six months, testosterone therapy should not be started (or should be stopped if already underway). Alternative treatments that stimulate your body’s own testosterone production while preserving sperm are available. For those with a longer timeline of 6 to 12 months, some protocols combine low-dose testosterone with medications that maintain sperm production. If fatherhood is more than a year away, a cycling approach, alternating periods on and off therapy, can be used to keep that option open. This is a conversation to have before your first dose, not after.
Lifestyle Changes May Come First
Obesity, poor sleep, chronic stress, and excessive alcohol use all suppress testosterone. In some men, addressing these factors can raise levels enough to resolve symptoms without medication. Losing significant body fat, in particular, has a well-documented effect on testosterone production. Treating obstructive sleep apnea can also improve hormone levels.
Guidelines don’t specify a required waiting period for lifestyle interventions before starting therapy, but if your levels are borderline (say, in the 250 to 350 ng/dL range) and you have clear modifiable risk factors, trying those changes for three to six months and retesting is reasonable. If your levels are very low, you have a clear medical cause like a pituitary disorder or testicular injury, or your symptoms are significantly affecting your daily life, there’s less reason to delay.
How Long Before You Know It’s Working
Testosterone therapy isn’t an overnight fix, but different symptoms respond on different timelines. Knowing what to expect keeps you from abandoning treatment too early or waiting too long on something that isn’t helping.
Sexual interest is one of the first things to shift, often within three weeks, with a plateau around six weeks. Improvements in mood and general quality of life typically begin around three to four weeks, though depression-related benefits may take 18 to 30 weeks to fully develop. Erectile function and ejaculation can take up to six months to noticeably improve.
Body composition changes are slower. Reductions in fat mass and gains in lean muscle start appearing at 12 to 16 weeks and stabilize around 6 to 12 months, with marginal improvements continuing beyond that. Bone density improvements take at least six months to become measurable and continue building for three years or more. Red blood cell production increases around three months and peaks at 9 to 12 months, which is one reason regular blood monitoring is important during that first year.
If you’ve been on therapy for six months with good blood levels and see no meaningful symptom improvement, it’s worth revisiting the diagnosis. Low testosterone may not have been the primary cause of your symptoms.
Age Alone Isn’t a Reason to Start
Testosterone declines naturally with age, roughly 1 to 2 percent per year after age 30. That gradual drop is normal and doesn’t automatically warrant treatment. The same diagnostic standard applies regardless of age: confirmed low levels plus symptoms. A 55-year-old man with a testosterone level of 280 ng/dL and no real complaints is not a strong candidate for therapy. A 35-year-old with the same level who has lost his sex drive, can’t concentrate, and is losing muscle mass is.
Therapy does appear to be particularly effective in younger men with very low levels, but older men with genuine deficiency also benefit. The deciding factor is not your birthday. It’s whether your lab values and your lived experience both point in the same direction.