Testosterone replacement and fertility: what TRT does to sperm

Written by Mr Maj Shabbir FRCS(Urol), Consultant Urological Surgeon & Andrologist · 22 October 2026

Testosterone replacement therapy (TRT) can make a real difference to a man with genuine testosterone deficiency. It also suppresses sperm production, in many men to zero, and that trade-off is explained far too rarely. This guide covers why it happens, how quickly, whether it recovers, and what to do if you are on testosterone and want children — or are the partner of someone who is.

Does testosterone replacement affect fertility?

Yes. Testosterone replacement suppresses sperm production for as long as you take it, usually to zero. That is its expected effect, not a rare side effect.

A British Society for Sexual Medicine (BSSM) guideline states that in younger men testosterone therapy frequently causes infertility, and that long-term use is associated with azoospermia — no sperm in the ejaculate at all. This applies to every form of replacement, whether gel, injection or implant, and whether it was prescribed or not. It does not make TRT a bad treatment: BAUS advises that it should be considered when a man has significant symptoms and reduced blood levels of active testosterone. It means fertility has to be part of the decision.

Why does taking testosterone switch off sperm production?

Because your brain reads the testosterone you take as a sign that you already have enough, and turns down the hormone signals that tell your testicles to work.

Testosterone is made in the testicles under instruction from the pituitary gland at the base of the brain. The pituitary sends two messenger hormones: LH, which tells the testicles to make testosterone, and FSH, which supports sperm production. The system regulates itself like a thermostat. When testosterone is high, the pituitary sends less LH and FSH; when it is low, it sends more.

When testosterone arrives from outside, through a gel or injection, the pituitary sees a normal or high level and turns LH and FSH down. The BSSM guideline describes exactly this: external testosterone reduces the body’s own production through negative feedback in the hormone axis. Without those signals the testicles go quiet. They stop making their own testosterone, and with it the local hormone environment that sperm production depends on. Testosterone reaching the testicles from the bloodstream does not replace that. This is why a man on TRT can have a perfectly good testosterone level on his blood test and almost no sperm.

How quickly does TRT affect fertility?

Not overnight, but there is no reliably safe period: the BSSM guideline describes testosterone therapy in younger men frequently causing infertility after 6 to 12 months of treatment.

Two things make timing hard to judge. First, sperm take around 74 days to develop, so a semen sample reflects production that began weeks earlier; an early normal result does not tell you where things will settle. Second, the degree of suppression varies between men. For that reason, if you are on testosterone and want children, I would rather you had a semen analysis than an assumption.

Is infertility from TRT reversible?

Usually, but not always and not quickly. The BSSM guideline reports that in younger men the effect reverses in 60% to 70% within 9 to 12 months.

The remainder take longer: recovery can take many months to years, and in a minority it is incomplete. The longer and the higher the dose of testosterone or anabolic steroids, the less certain it is that the system will restart on its own. When it does not, the problem is usually treatable: treatment aims to restart your own production rather than replace it, and hormonal treatment can restore sperm production when suppression is the cause.

Recovery is tracked with repeat semen analyses, a few months apart, because each check reflects a new cycle of sperm production. If sperm do not return despite treatment, there are still routes to a family, which I set out in the guide to having children with azoospermia.

Do anabolic steroids and gym testosterone have the same effect?

Yes. Anabolic steroids suppress the same pituitary signal, and the NHS lists reduced sperm count, infertility and shrunken testicles among their effects in men.

BAUS also notes strong evidence that anabolic steroids or growth hormones, taken alongside protein shakes, can adversely affect fertility. I see men every year whose azoospermia was caused by a prescription, or by a gym supply, that nobody warned them about. If this applies to you, tell your specialist exactly what you have taken and for how long, including past use. Anabolic steroids are one of the drug-related causes I look for in any assessment of male infertility, and after prolonged or high-dose use the system does not always restart on its own.

I am on TRT and want children. What should I do?

Do not simply stop overnight. Arrange a specialist review, so that testosterone is withdrawn or switched in a planned way while your hormones and semen are checked.

Stopping abruptly can backfire. Your own production has been switched off, so stopping leaves you with low testosterone, and the symptoms that led to treatment, until your system restarts. A planned approach usually looks like this:

1. A semen analysis, to establish where you are now. The semen analysis guide explains how to give a reliable sample.
2. A hormone profile — testosterone, LH, FSH and prolactin — to show how suppressed the system is and to look for an underlying cause.
3. A review of the original diagnosis, because some men are started on testosterone after a single, badly timed blood test.
4. A plan to come off, or switch to a treatment that stimulates your own testicles, with semen re-checked over the following months.
5. Sperm storage as insurance if sperm are present, so that a sample is banked while treatment changes.

It also makes sense for your partner to be assessed at the same time. One important exception: if your testosterone was low because the testicles themselves are failing (primary hypogonadism), stopping replacement will not restore production in the same way, and the plan looks different — sometimes including surgical sperm retrieval for IVF with ICSI.

Can low testosterone be treated without losing fertility?

Often, yes. In secondary hypogonadism, medicines that stimulate your own testicles can raise testosterone while maintaining sperm production.

The distinction is between primary hypogonadism, where the testicles are failing and LH and FSH are high, and secondary hypogonadism, where the testicles are capable but the pituitary signal is inadequate. Secondary hypogonadism is frequently reversible, and for most men who still want children, fertility-sparing treatment is the right route — yet it is under-offered. The first step is often not a prescription at all: weight loss, treating obstructive sleep apnoea, reviewing opioid painkillers and stopping anabolic steroids can restore levels without replacement. In primary hypogonadism, treatment is usually lifelong, which is exactly why sperm storage before starting is worth considering. The low testosterone page covers assessment and treatment in full.

Can I get pregnant if my husband is on TRT?

It is possible, but less likely. Testosterone usually suppresses sperm production, often to zero, yet it is not a contraceptive and cannot be relied on to prevent pregnancy.

Suppression is common but not universal, and it varies between men and over time. The only way to know his current count is a semen analysis. If you are trying to conceive, do not wait to see what happens: book a specialist review for him, and have your own fertility assessed in parallel. If you are over 35, the usual advice is to seek help after about six months of trying rather than twelve. If you do not want a pregnancy, use contraception. And if he stops testosterone in order to conceive, expect recovery to take months rather than weeks.

How should low testosterone be confirmed before starting TRT?

With two morning blood samples, taken before 10am, fasting, on separate days, alongside SHBG, LH, FSH and prolactin, rather than one test taken at a random time.

Testosterone follows a daily rhythm and is highest in the morning, so an afternoon sample can look falsely low; this is a common source of misdiagnosis. Symptoms such as fatigue, low mood and poor libido are not specific to testosterone deficiency, and the NHS notes that in many cases they have nothing to do with hormones. LH and FSH separate primary from secondary causes, which, as above, determines whether fertility can be protected. If you were started on testosterone after a single test, or nobody asked about your plans for children, it is worth reviewing before going further. If children are part of your plans, you can book a consultation; the first appointment can be by video or telephone.

Sources and further reading

1. BSSM: Guidelines on Adult Testosterone Deficiency, With Statements for UK Practice (2017)
2. NHS: Anabolic steroid misuse (reviewed Jan 2026)
3. BAUS: Fertility problems (Mar 2024)
4. BAUS: Male menopause (androgen deficiency in the ageing male) (Mar 2024)
5. NHS: The ‘male menopause’ (reviewed Oct 2022)
6. BAUS leaflet: Male fertility tests, A23/041 (published Mar 2024)