Do I need blood tests before starting TRT?

Yes. TRT is only started once low testosterone is biochemically confirmed, usually on two separate morning samples, alongside a wider baseline panel covering hormone, blood count, prostate and liver markers. This applies whether you are treated on the NHS or privately.

How often will I need blood tests once I'm on TRT?

Most UK programmes test again around 3 months after starting or after a dose change, again at 6 months, then every 6 to 12 months once things are stable. Testosterone level, haematocrit and, where age-appropriate, PSA are checked at each round.

What happens if my haematocrit is too high on TRT?

TRT can thicken the blood by raising red cell mass. If haematocrit rises above a safe threshold, a clinician will typically reduce the dose, space out injections, or arrange venesection, a blood donation style procedure, to bring it back down, then re-test before continuing.

Are TRT blood tests available on the NHS?

Yes, if you are being investigated or treated for suspected hypogonadism through your GP or an NHS endocrinology service, the relevant baseline and follow-up bloods are funded as part of that pathway. Private testing is generally faster to arrange and interpret, which is the main reason people choose it.

How much do TRT blood tests cost privately?

A baseline workup, covering the consultation and full panel, commonly costs £150 to £400 privately in the UK. Follow-up monitoring rounds are usually £60 to £120 each if billed separately, though some programmes bundle monitoring into the ongoing monthly fee instead.

Men's Health

TRT and fertility: what you need to know

Reviewed by the My London Pharmacy clinical team, Yvonne Lim, Pharmacist Independent Prescriber ·31 August 2026 ·7 min read

Quick answer

Testosterone replacement therapy commonly reduces or stops natural sperm production, because it suppresses the hormone signals (LH and FSH) that drive it, so this should always be discussed before starting if you may want children. The effect is usually reversible after stopping, though recovery can take several months to a year or more and isn't certain for every man.

Fertility is one of the most important things to discuss before starting TRT, and one of the most commonly overlooked. Testosterone replacement therapy treats the symptoms of low testosterone effectively, but it does this in a way that typically reduces natural sperm production at the same time. This guide explains why, whether it's reversible, and what your options are if fertility matters to you now or in the future. None of this means TRT is off the table if you might want children eventually; it means the conversation needs to happen before you start, not after.

It's a topic that's easy to put off, particularly if children feel like a distant, hypothetical prospect rather than an immediate plan. But because the effect on fertility begins as soon as you start treatment, and because recovery afterwards isn't instant, "distant, hypothetical" is exactly the point at which this is worth discussing, not something to leave until it becomes urgent.

How TRT affects fertility

When you take exogenous testosterone (testosterone from outside the body, as a gel, injection or other formulation), your circulating testosterone level rises. Your brain detects this and responds by reducing the hormone signals it normally sends to the testes, which are the very signals that drive sperm production. The result is that sperm production commonly falls, and in many men it stops almost entirely while they remain on treatment.

Why this happens: the biology in brief

Testosterone production and sperm production are both controlled by a feedback loop between the brain and the testes. The pituitary gland releases luteinising hormone (LH) and follicle stimulating hormone (FSH), which stimulate the testes to produce both testosterone and sperm. When testosterone is supplied from outside the body, the brain senses that levels are already high and reduces LH and FSH output accordingly. Less LH and FSH means less of the testicular stimulation that sperm production depends on, even though the testosterone level itself, measured in the blood, looks normal or high.

This is also why a blood test showing a healthy testosterone level while on TRT tells you nothing about your current fertility. The two are regulated by the same feedback loop, but pulling on one side of it, artificially raising blood testosterone, actively works against the other.

Four-step graphic showing how TRT raises testosterone, reduces natural signalling, lowers sperm production, and should be discussed before starting

Is the effect reversible

For most men, sperm production recovers after stopping TRT, but the timeline varies considerably and isn't instant. Recovery commonly takes several months, and for some men can take a year or more, depending on factors including how long TRT was used, the dose, and individual variation in how quickly the hormonal feedback loop resets. Full recovery isn't certain for every man, which is exactly why this is a conversation worth having before starting, not after.

Options if you want to preserve fertility

If having children in the near future is a possibility, it's worth raising this at your very first consultation. Sperm banking (cryopreservation) before starting treatment is a straightforward, well-established option that gives you a safeguard regardless of what happens to your fertility while on treatment. Some clinicians may also consider alternative approaches aimed at supporting natural testosterone production while preserving fertility, but these are individual, specialist decisions made case by case.

It's also worth thinking about timing more broadly, not just the immediate decision to start or delay TRT. If children are a firm plan for the next year or two rather than a distant possibility, that's a very different conversation from "maybe one day," and it's worth being specific with your clinician rather than leaving it vague.

What to discuss before starting TRT

Before starting, it's worth telling your clinician clearly whether you want children now, in the next few years, or not at all. This single piece of information can genuinely change the approach discussed with you, including whether TRT is the right first step or whether fertility preservation or an alternative should be considered alongside or instead of it. It's also worth mentioning if your partner is already, or might soon be, undergoing her own fertility investigations, since the timing of both partners' plans can matter together.

If you're already on TRT and thinking about fertility

If your circumstances have changed since starting TRT and fertility is now a consideration, raise it with your clinician rather than stopping treatment abruptly on your own. A semen analysis can establish where things currently stand, and your clinician can talk through a supervised plan, whether that's a planned pause, a change in approach, or simply a realistic timeline to work towards.

Stopping TRT on your own without a plan isn't the safest route, even though it might seem like the obvious first step. Coming off treatment abruptly can mean a period of low testosterone symptoms returning before your natural production has properly picked back up, on top of an uncertain fertility timeline. A supervised approach gives you a much clearer picture of where things genuinely stand and what to expect next.

It's also worth having this conversation even if you're not yet certain fertility matters to you. Circumstances change, and a clinician who already knows your history and current bloods is far better placed to help you plan than one meeting you for the first time after the decision has become urgent. There's no downside to raising it early, even as a "just in case" question at a routine monitoring appointment.

Frequently asked questions

Does TRT affect fertility?

Yes. TRT commonly reduces or stops natural sperm production because it suppresses the hormone signals (LH and FSH) that drive it, even though blood testosterone levels themselves look normal or high.

Why does testosterone therapy lower sperm count?

Exogenous testosterone causes the brain to reduce LH and FSH output through a natural feedback loop, and it's LH and FSH that stimulate the testes to produce sperm, so less signalling means less sperm production.

Does fertility recover after stopping TRT?

Usually, yes, though recovery can take several months to a year or more and isn't certain for every man. The timeline depends on factors including how long TRT was used and individual variation.

Can I preserve fertility before starting TRT?

Sperm banking before starting treatment is a well-established option. It's worth raising fertility plans at your first consultation so this can be discussed before you begin.

What should I do if I want children while on TRT?

Talk to your clinician rather than stopping treatment abruptly on your own. A semen analysis can show where things stand, and your clinician can plan a supervised next step with you.