Does TRT Affect Fertility? What the Evidence Actually Shows

Written by Francesca Steyn, NMC-registered fertility practitioner

Testosterone is having a moment. Podcasts, clinics and gym conversations are full of talk about "low T", and testosterone replacement therapy, or TRT, is being framed as a fix for tiredness, low mood and stalled progress in the gym. One question gets far less airtime than it should: does TRT affect fertility? The short answer is yes, it usually does, and often more than men expect. If you are thinking about starting TRT, or you are already on it and hoping to have children, this is worth understanding before you go any further.

As featured in Men's Health. Malebox appears in the current issue of Men's Health, the same issue that runs a major feature questioning whether men are being pushed to worry about "low T". We think the answer is not to panic, and not to dismiss it either, but to know your actual numbers.

How TRT Affects Sperm Production

It helps to know how the body makes sperm. Your brain and your testes talk to each other through a feedback loop. The brain releases hormones that signal the testes to produce both testosterone and sperm. When you take testosterone from an external source, the brain reads your levels as high and dials down those signals. Testosterone production inside the testes falls, and sperm production tends to fall with it. The NHS notes that anabolic steroids and testosterone-containing medicines are a recognised cause of a low sperm count for exactly this reason.

This is not a rare side effect. It is the expected biological response, and it is well documented in the andrology literature. A widely cited review describes exogenous testosterone as "a preventable cause of male infertility", because suppression of sperm production is so consistent. In studies of testosterone used as a male contraceptive, sperm counts fell to one million per millilitre or fewer in the large majority of men within four to six months, and many men reached azoospermia, meaning no sperm in the sample at all. A clinical review of TRT and anabolic steroid use reports an average time to azoospermia of around 120 days. In other words, for many men TRT works as an effective contraceptive, which is the opposite of what someone trying for a baby wants.

Is the Effect Reversible?

For most men, the news here is reassuring. Sperm production usually recovers after stopping TRT, though it takes time and the timeline varies a lot from person to person.

The most authoritative figures come from an integrated analysis of 30 studies published in The Lancet (Liu et al, 2006), which tracked sperm recovery after hormonal suppression. It found that the typical probability of sperm recovering to 20 million per millilitre was 67 percent within 6 months, 90 percent within 12 months, 96 percent within 16 months, and 100 percent within 24 months. More recent clinical reviews report similar recovery rates, often quicker when supported by a specialist.

The same research highlights two things that influence how quickly recovery happens: age and how long you have been taking testosterone. Younger men who have used TRT for a short time often rebound within three to six months. Older men, or those who have been on it for years, may need a year or more. None of this is guaranteed, which is exactly why it is worth making informed decisions early rather than discovering the effect by accident. Researchers have also warned that TRT is too often prescribed to men in infertile couples without the fertility consequences being explained first.

"Low T" and the Importance of Real Numbers

There is a second issue tangled up in all of this. A lot of men are being encouraged to worry about low testosterone without ever measuring it. Symptoms like fatigue, low mood, poor recovery and reduced libido are real, but they are also non-specific, which means they can have many causes that have nothing to do with testosterone.

UK guidance from the British Society for Sexual Medicine is clear that diagnosis should be based on blood tests, not symptoms alone. As a guide, the guidelines point to a total testosterone below 8 nmol/L as a level that usually warrants treatment, above 12 nmol/L as a level that usually does not, and a symptom-led conversation in between. Crucially, they recommend two separate morning samples, taken between 8 and 11am, because testosterone is naturally highest then and fluctuates day to day. A single number taken at the wrong time of day can be misleading.

The takeaway is simple. Before you accept that your testosterone is low, and certainly before you start a therapy that can switch off your fertility, it is worth knowing your actual numbers.

What This Means in Practice

If having children is on your radar, now or in the next few years, factor fertility into any conversation about TRT before you start, not after. There are approaches a specialist can discuss that aim to support testosterone-related symptoms while protecting sperm production, and there are options for preserving fertility, but these decisions are far easier to make at the start.

If you are already on TRT and trying to conceive without success, this is worth raising with a clinician sooner rather than later. Stopping under guidance, and giving your body time, restores sperm production for most men.

And if you simply want to understand where you stand, a baseline picture is a sensible starting point. A male factor is involved in around half of all fertility cases, yet most men have never had their sperm or hormones checked. A home test that measures sperm quality against WHO reference values alongside a hormone profile gives you real data on both the fertility and the testosterone questions at once, with a clinician to talk you through what it means. That is the thinking behind the Malebox Home Sperm Test and Male Hormone Profile, which pairs a lab semen analysis with a hormone panel and a one-to-one consultation with a fertility nurse.

Frequently Asked Questions

Q: Does TRT make you infertile permanently? A: Usually not. TRT suppresses sperm production for as long as you take it, but for most men sperm recovers after stopping, with around 90 percent returning to a normal count within 12 months. Older men and long-term users may take longer, and recovery is not guaranteed.

Q: How quickly does TRT lower sperm count? A: Quite quickly. Studies show significant suppression within three to six months of starting, with many men reaching very low or zero sperm counts by the six-month mark. The average time to no measurable sperm is around four months.

Q: Can I take TRT and still have children? A: It is difficult while on TRT, because it usually suppresses sperm production. Some men work with a specialist on alternatives that support symptoms without shutting down fertility. If children are a priority, discuss this before starting.

Q: Should I get my testosterone tested before starting TRT? A: Yes. UK guidance recommends diagnosing low testosterone with blood tests rather than symptoms alone, ideally two morning samples. Testing first tells you whether your level is genuinely low and gives you a baseline before any treatment.

Q: How do I check my fertility at home? A: An at-home sperm test analyses a sample in a lab against WHO reference values for things like count, motility and morphology. Some tests, including Malebox, add a hormone profile and a consultation so you understand both your sperm health and your testosterone in one go.

Testosterone is worth understanding, not fearing. The men who make the best decisions about it are the ones working from real numbers rather than headlines. Whether you are weighing up TRT, trying for a baby, or simply curious about where you stand, a clear picture of your sperm health and your hormones is a calm and sensible place to begin.

Sources and Further Reading

• Men's Health, where Malebox features in the current issue alongside its coverage of testosterone and "low T".

• NHS, Low sperm count, causes including testosterone and anabolic steroid use.

• British Society for Sexual Medicine, Guidelines on Adult Testosterone Deficiency, Journal of Sexual Medicine, diagnostic thresholds and testing.

• Liu PY et al, Rate, extent, and modifiers of spermatogenic recovery after hormonal male contraception: an integrated analysis, The Lancet, 2006.

• Understanding and managing the suppression of spermatogenesis caused by testosterone replacement therapy and anabolic-androgenic steroids, clinical review.

• Crosnoe LE et al, Exogenous testosterone: a preventable cause of male infertility, Translational Andrology and Urology.

• Misuse of testosterone replacement therapy in men in infertile couples and its influence on infertility treatment.

• World Health Organization 2021 reference values for semen analysis, impact in clinical practice.

Francesca Steyn is an NMC-registered fertility practitioner with over 20 years in reproductive health. She has served on the NICE guideline committee and the HFEA legislative reform group.