TRT stands for testosterone replacement therapy. A doctor prescribes testosterone because your body no longer makes enough of it. In the Netherlands that usually means an injection or a gel, and normally only after two separate morning measurements have shown a low testosterone level.
Most pages skip that last part.
I read the first ten Dutch search results on TRT before writing this. Two came from a clinic that sells the treatment. One came from a forum about anabolic steroids, one from a pharmacy with no Dutch branch.
Not one of those ten pages explained what external testosterone does to your own production and to your sperm count. That is quite a thing to leave out for a 34-year-old who still wants children. So this article makes room for it, alongside the forms, the side effects and the values that run alongside treatment.
What exactly is TRT?
TRT is testosterone as a medicine, prescribed when your body structurally makes too little of it. That state is called hypogonadism. The goal is not the highest possible number but a level back inside the normal adult male range, together with the symptoms that go with it.
Hypogonadism comes in roughly two flavours. In the primary form the testicles themselves have gone quiet while the brain shouts louder, so LH and FSH run high. In the secondary form the problem sits higher up, in the pituitary or hypothalamus, and LH and FSH are low or simply normal while your testosterone is not.
That distinction is not a detail. It decides whether external testosterone makes sense, or whether something else needs investigating first. Basaria described the split in The Lancet in 2014 as the starting point of any assessment.
Our page on LH and FSH in men covers how those two hormones relate to your testosterone.
When does a doctor consider testosterone therapy?
A doctor considers testosterone therapy when symptoms and laboratory values point the same way. Symptoms alone are too vague, because tiredness, low sex drive and a short fuse have dozens of causes. A single low result is not enough either, since testosterone swings by the day and by the hour.
That is why blood is nearly always drawn twice, in the morning, fasted or at least early. The Endocrine Society noted in its 2018 review that one low value is not enough to call it a deficiency.
Two men can both land on 9.5 nmol/l and still have completely different conversations with their doctor. One is 61, sleeps badly, has gained twelve kilos over a few years and has a high SHBG. The other is 29, trains four times a week and has an LH of 1.2, meaning the signal from above is not arriving.
With the first man a doctor often looks at weight, sleep and apnoea first. With the second the attention moves to the pituitary. Same number, two different routes.
What strikes me is that online you almost only ever see that one number. In practice the context around it matters far more.
Which forms of testosterone therapy exist in the Netherlands?
The Netherlands has four practical forms: a long-acting injection, a shorter injection with a mix of esters, a gel for the skin and capsules taken by mouth. They differ mainly in how often you use them and how flat or how jagged your level runs as a result.
| Form | Brand name in the Netherlands | How often | What it does to your level |
|---|---|---|---|
| Injection with testosterone undecanoate | Nebido | every 10 to 14 weeks | long, reasonably flat curve with a peak in the first weeks |
| Injection with a mix of esters | Sustanon 250 | every 2 to 3 weeks | faster peak and a clearer trough towards the end |
| Gel on the skin | Androgel, Testogel, Tostran | every day | daily fluctuation, the level follows your application time |
| Capsules by mouth | Andriol Testocaps | two to three times a day | short acting and dependent on the fat in your meal |
The Farmacotherapeutisch Kompas lists dosing, contraindications and side effects per preparation. It is the most sober Dutch source available and it is free online.
Choosing between these forms is something you do with your doctor. Some men like one injection a quarter, others prefer to hold the dose in their own hands every day. Both arguments are legitimate.
We go deeper per form on Nebido, on testosterone gel such as Androgel and on Sustanon.
What do you notice on TRT, and when?
The effects do not arrive together. Sex drive and mood shift first for many men, often within weeks. Changes in muscle mass and fat distribution take months, and bone density takes longer still. That ordering surprises almost everyone who starts.
Bhasin and colleagues described in 2018 that the timeline differs sharply per outcome. Libido and energy tend to respond fastest, body composition slowest.
That makes the first month a poor yardstick. You may already feel something while your level is nowhere near stable.
With the long-acting injection this is especially confusing. After the first shot and the loading shot that follows, it usually takes several cycles before the pattern becomes repeatable.
Which side effects are reported most?
The most commonly reported side effects are acne, oilier skin, increased production of red blood cells, fluid retention and tender or swollen breast tissue. Injections add pain at the injection site. How often they occur differs per form and per person.
Heart and vessels were unclear for years. The TRAVERSE trial by Lincoff and colleagues, published in The New England Journal of Medicine in 2023, followed more than five thousand men with low testosterone and raised cardiovascular risk. Testosterone gel did not lead to more heart attacks or strokes than placebo in that group.
That is reassuring, but it is not a free pass. The same trial saw more atrial fibrillation, pulmonary embolism and acute kidney injury in the testosterone arm.
Tender breast tissue is one of the most underrated complaints. It happens because part of your testosterone converts into oestradiol. Our piece on gynaecomastia in men covers what goes on there.
Why does your doctor watch your haematocrit?
Testosterone stimulates the production of red blood cells. That can push up your haematocrit, the share of your blood made up of red cells. If that share climbs too high your blood flows more thickly, which is why this value nearly always runs alongside testosterone therapy.
Ohlander and colleagues mapped how often this happens in Sexual Medicine Reviews in 2018. In their review injections raised it clearly more often than gels did. Jones had already flagged it in older men in 2015.
It is the side effect you can follow most easily yourself, because it appears as a plain number on a blood result. Our marker page on haematocrit explains what the value means.
If you smoke, that counts too. Smoking raises your haematocrit independently of any treatment.
What does TRT do to your fertility?
Testosterone from outside suppresses your own production. Your brain sees a generous level, dials LH and FSH back, and those two hormones are exactly what drive sperm production in your testicles. In many men the sperm count drops sharply as a result, sometimes to near zero.
Fusco and colleagues described this mechanism in detail in 2021. Crosnoe and colleagues had already called external testosterone a preventable cause of male infertility back in 2013.
In some men sperm production recovers after stopping, but that can take months to more than a year, and it does not return equally fully in everyone.
This is where I think commercial pages fall short. If you want children, or have not ruled it out, this conversation belongs before the first injection rather than after it. Other routes exist, and we cover one of them in our piece on clomiphene in men.
If you want to know what a semen analysis actually reports, see semen analysis values.
Is TRT the same as a testosterone cycle?
No. TRT is a prescribed treatment that brings your level back into the normal adult male range. A cycle of anabolic steroids aims at values far above it, often with several compounds at once, usually without a doctor and without blood monitoring.
So the difference is not the molecule. It is the dose, the supervision and the goal.
The Netherlands has unusually good data here. In the HAARLEM study researchers followed a group of Dutch men before, during and after a self-run cycle. Smit summarised the findings in 2022: changes in blood lipids, in haematocrit and in testicular function were clearly measurable, and did not always recover fully.
De Ronde described what happens to testicular function in the same year. Smit had already published an overview of the Dutch outpatient clinic these men can attend in 2018.
That makes the HAARLEM numbers useful even if you never touch a cycle. They show which values move with testosterone, and that is precisely the list a careful treatment follows.
Which blood values run alongside testosterone therapy?
During testosterone therapy a doctor usually looks at more than testosterone alone. The fixed core is your testosterone level, your haematocrit and your PSA. Oestradiol often joins them, and depending on your situation LH and FSH as well.
| Value | Why it is followed |
|---|---|
| Total testosterone | shows whether the dose brings your level into the normal range |
| Free testosterone | the fraction not bound to protein, relevant when SHBG is unusual |
| Haematocrit | rises on testosterone and is the most closely followed side effect |
| PSA | prostate value often recorded before and during treatment |
| Oestradiol | part of your testosterone converts into it, which can explain breast symptoms |
| LH and FSH | show how far your own production has been dialled back |
When and how often that happens is for your treating doctor to decide. It depends on your form of therapy, your baseline values and your symptoms, and it is not something an article can put a number on.
If you want to know in advance roughly what gets measured, see our piece on blood values before you start TRT and on monitoring testosterone therapy.
You can record a baseline yourself with a testosterone test. What gets measured is explained on the marker pages for total testosterone and free testosterone.
What if testosterone therapy does not suit you?
Not every low result calls for testosterone from outside. Sleep debt, heavy excess weight, a lot of alcohol, chronic stress and a raised prolactin can all pull your value down. In those cases a doctor often looks at the cause first.
Ide and colleagues set out in 2020 which routes exist in secondary hypogonadism when external testosterone is not the first choice. Clomiphene is the best known of them, and Wheeler described how it works in men in 2019.
Thuisarts offers plain Dutch-language explanations of fatigue and hormone complaints, written for patients rather than for prescribers.
What does and does not work without medication is something we went through in raising testosterone naturally.
What it comes down to
TRT is a serious medicine with a serious effect on your own hormone balance, and the question is never only whether your value is low. The question is why it is low, what you still have riding on having children, and which values run alongside it once you start.
My advice to any man weighing this up stays the same: do not go shopping for a clinic that says yes with one result in your pocket.
Take your symptoms and your results to your GP and ask about the route that fits your situation. If you want to know where you stand first, record a baseline and discuss it.
Every blood test result includes a professional assessment from a BIG-registered doctor. For treatment decisions, discuss your results with your GP.
References
- Bhasin S, et al. Testosterone therapy in men with hypogonadism. Journal of Clinical Endocrinology and Metabolism, 2018. PMID 29562364
- Lincoff AM, et al. Cardiovascular safety of testosterone-replacement therapy. New England Journal of Medicine, 2023. PMID 37326322
- Basaria S. Male hypogonadism. The Lancet, 2014. PMID 24119423
- Ohlander SJ, et al. Erythrocytosis following testosterone therapy. Sexual Medicine Reviews, 2018. PMID 28526632
- Jones SD Jr, et al. Erythrocytosis and polycythemia secondary to testosterone replacement therapy in the ageing male. Sexual Medicine Reviews, 2015. PMID 27784544
- Fusco F, et al. Suppression of spermatogenesis by exogenous testosterone. Current Pharmaceutical Design, 2021. PMID 33292112
- Crosnoe LE, et al. Exogenous testosterone: a preventable cause of male infertility. Translational Andrology and Urology, 2013. PMID 26813847
- Ide V, et al. Treatment of men with central hypogonadism: alternatives for testosterone replacement therapy. International Journal of Molecular Sciences, 2020. PMID 33375030
- Wheeler KM, et al. Clomiphene citrate for the treatment of hypogonadism. Sexual Medicine Reviews, 2019. PMID 30522888
- Smit DL, et al. Health effects of androgen abuse: a review of the HAARLEM study. Current Opinion in Endocrinology, Diabetes and Obesity, 2022. PMID 35938779
- de Ronde W, et al. Anabolic-androgenic steroid abuse and testicular function in men. Current Opinion in Pharmacology, 2022. PMID 36410315
- Smit DL, et al. Outpatient clinic for users of anabolic androgenic steroids. Netherlands Journal of Medicine, 2018. PMID 29845939
- Farmacotherapeutisch Kompas, testosterone monographs. Accessed 2026.
Autor
Caliberhealth
Dr. Naimi, lekarz wpisany do holenderskiego rejestru BIG, nadzoruje standardy medyczne naszych treści i ocen. Przeczytaj naszą politykę medyczną
