Testosterone therapy (often called TRT) can lower a man's sperm count, sometimes to zero, and some men start it without hearing that. I am a urologist, and I want every man to know this before his first prescription.
This article explains why the effect happens, how strong it is, what the research shows about recovery and what to plan before you start.
How Testosterone Therapy Lowers Sperm Production
Your brain and your testes work as a feedback loop. A part of the brain called the hypothalamus sends a signal to the pituitary gland. The pituitary then releases two hormones into the blood: luteinizing hormone (LH) and follicle-stimulating hormone (FSH).
LH tells the testes to make testosterone, and FSH works with that testosterone to make sperm. Sperm production needs a high level of testosterone inside the testes. When testosterone rises, the brain releases less LH and FSH, and this feedback keeps your levels steady.
Testosterone therapy adds testosterone from outside the body. The brain senses the higher blood level and cuts its signal, so LH and FSH fall below the levels that sperm production needs.
With little LH, the testes make less of their own testosterone. The level inside the testes falls, even as the level in the blood rises. Without enough FSH and local testosterone, sperm production slows or stops, and the testes can shrink.
That is how a man can have a good blood testosterone level and a very low sperm count at the same time.
How Often Sperm Count Falls to Zero
Researchers have tested testosterone as a form of male birth control, and those trials show how strong the effect can be.
In a World Health Organization (WHO) trial published in 1990, 271 healthy, fertile men received testosterone injections. Of those men, 157 reached a sperm count of zero in three semen samples in a row. The estimated rate of reaching zero by 6 months was 65%, and the average time to reach zero was 120 days.
Not every man reached zero, and in 11 men sperm came back during the trial. Even among the men at zero, one pregnancy occurred while couples relied on the injections. A 2019 review in the World Journal of Men's Health calls testosterone a poor contraceptive.
Keep one point in mind: these trials aimed to stop sperm production on purpose, in healthy volunteers. Men who take testosterone for low levels are a different group, and results vary from man to man.
How Long Sperm Takes to Come Back
To see what happens after men stop, a 2006 analysis in The Lancet pooled data on 1,549 healthy men from 30 studies. It measured how long sperm counts took to return to 20 million per mL, a level the authors used as a marker of fertility.
The median time to reach that level was 3.4 months. The chance of recovery was 67% within 6 months, 90% within 12 months, 96% within 16 months and 100% within 24 months.
Recovery was slower in men who used hormones for longer and in men who used longer-acting testosterone products. It was faster in men with higher sperm counts before treatment. The authors found that each of these factors had only a small effect.
In the 1990 WHO trial, after the injections stopped, the median time from zero back to each man's own starting count was 6.7 months.
What we don't know: these numbers come from controlled trials of healthy volunteers aged 18 to 51. The trials also limited how long men used testosterone. The 2019 review notes that the extent of recovery is not clear for long-term users.
The review also reports that the effect on sperm varies with the form of testosterone, and it calls for more research on each form. So recovery is likely for most men, but I cannot promise it for any one man.
If sperm does not return, a couple may need assisted reproduction, such as in vitro fertilization. The review notes that these treatments are expensive and do not always work, which is one more reason to plan before you start.
From our practice: A man in his mid-30s came to us already on testosterone. An outside lab had found a borderline low level, and a stand-alone testosterone clinic started treatment. No one had discussed his fertility.
We talked through the fertility risk first. He paused testosterone so we could get a new baseline. We then checked a full panel: LH, FSH, total and free testosterone, SHBG and the other labs his history called for.
His own testosterone was only mildly low. So we chose a treatment aimed at helping his body make more of its own testosterone. We also ordered a semen analysis and referred him to a fertility specialist to discuss his options.
What Guidelines Say
The American Urological Association (AUA) guideline on testosterone, published in 2018 and reconfirmed in 2024, makes three main points about fertility risk.
First, men with low testosterone who are interested in fertility should have a reproductive health evaluation before treatment. Second, doctors should discuss the long-term effect of testosterone on sperm production with men who want children in the future. Third, doctors should not prescribe testosterone therapy to men who are trying to conceive now. The AUA rates the second and third points as strong recommendations.
The guideline also allows other medical approaches for men with low testosterone who want to stay fertile.
The risk has not always been clear, even to doctors. A survey of AUA members, run in 2010 and published in 2012, asked about treating male infertility. Of the urologists who answered, 25% said they would give testosterone to an infertile man while the couple tried to conceive. Only 387 urologists answered, about 5% of those asked, so the result may not reflect the whole field.
The 2019 review also notes that this effect can surprise patients, because testosterone can improve sex drive and erections.
The first question I ask: do you want children someday, and if so, when? "Not sure" is a fine answer, and it still shapes the plan.
Before You Start: A Checklist
If there is any chance you want children, cover these points before your first prescription.
Your family-planning timeline: children soon, children later and no plans at all each lead to a different plan. Tell your doctor even if the answer is years away.
A baseline semen analysis: the 2019 review recommends one for every man of reproductive age before testosterone therapy. It gives you a reference point if you need to check later.
Sperm banking: freezing sperm before you start keeps a sample in storage that does not depend on how your body recovers.
Fertility-preserving approaches: some ways of treating low testosterone aim to protect sperm production. They do not suit every man, so we choose them case by case.
The reason your testosterone is low: the AUA advises an LH test for men with low testosterone. It also advises a prolactin test when LH is low or low-normal. The cause can change the treatment, so it is worth finding first.
How We Approach It
At Kinetic Edge Health, the fertility conversation comes before any hormone decision. I am a urologist, and male fertility is part of my field. So the first visit covers your family plans along with your symptoms.
Our lab panel includes LH and FSH, not only testosterone, and we add a semen analysis before treatment when fertility matters to you. If testosterone therapy makes sense, we time it around your family plans. If it does not, we discuss other options, and either way we follow your labs over time.
This approach applies to both our sexual health care and our metabolic and hormonal care. Results vary from man to man, and we adjust the plan as your goals change.
Ask the Fertility Question First
Fertility is easier to protect than to restore. If there is any chance you want children, say so at your first visit. Then ask how the plan accounts for it, and expect a clear, specific answer.