TRT and Ejaculate Volume and Semen: What Really Changes

The question about ejaculate volume comes up in two contexts. The first is fear before therapy: 'will I have less semen after testosterone, and does that mean I will lose fertility?'. The second is an observation during treatment: 'since I started testosterone my ejaculate is clearly smaller — is that normal?'. In both cases it is worth separating three different concepts that blur together in everyday talk: ejaculate volume (how many milliliters of fluid), sperm concentration and count (how many cells are in that fluid), and fertility (the ability to conceive).

These three quantities depend on different organs and different hormonal mechanisms. Exogenous testosterone acts on them differently, which is why the simple slogan 'TRT reduces semen' can be both true (for sperm count) and misleading (for volume). In the sections below we take it apart.

Ejaculate is a mixture of three main fractions. Sperm, together with a small amount of fluid, come from the testicles and epididymides and make up only a fraction of the volume. By far the largest part of the fluid is produced by the seminal vesicles, and another substantial part by the prostate; a small contribution comes from the bulbourethral glands. That is why in men after vasectomy, who have no sperm in the ejaculate, semen volume is usually similar to before.

The seminal vesicles and prostate are androgen-dependent organs: for normal growth, secretion and contraction they need dihydrotestosterone and circulating testosterone. That matters, because it is precisely this circulating testosterone that TRT raises. In men with a genuine androgen deficiency, the accessory glands may be under-stimulated and ejaculate can be small; once the hormone level is corrected, their function should improve, not worsen. This mechanism is an argument that TRT alone should not systematically reduce ejaculate volume.

The semen-analysis reference values given by the World Health Organization (WHO) for the lower limit of volume are about 1.4–1.5 ml, depending on the edition of the manual; a typical value in healthy men usually falls within 2–5 ml. Volume also depends, however, on the abstinence period, hydration, age and frequency of intercourse, so a single measurement without these factors says little.

To understand the gap between sperm count and volume, you need to look at the hypothalamic–pituitary–gonadal axis. Testosterone supplied from outside is detected by the regulatory system as 'sufficient', so the pituitary reduces secretion of LH and FSH — the hormones that drive the testicles. LH stimulates Leydig cells to produce testosterone inside the testicles, and FSH together with a high local testosterone concentration sustains spermatogenesis. When gonadotropins fall sharply, the testicles produce less testosterone internally and fewer sperm.

The effect has been known for decades from research on male hormonal contraception. In an integrated analysis of 30 studies covering 1,549 healthy men taking androgens or androgens with a progestagen, sperm disappeared or fell dramatically in number over time and returned after treatment ended. In turn, in a paper on men on TRT, the authors point out that about 40% of those treated with testosterone develop azoospermia. For fertility that is an enormous change, but it does not concern the organs that determine ejaculate volume.

The reverse question — does testosterone increase ejaculate volume in men who have too little of it? — was examined in a randomized, double-blind, placebo-controlled trial. The result is surprising to many and shows how carefully simple associations must be treated.

How should this be interpreted? First, the trial does not show that testosterone reduces ejaculate volume — it shows that in men with low testosterone and reported ejaculatory problems (including reduced volume), giving testosterone did not improve symptoms significantly more than placebo. Second, the abstract does not report a result for ejaculate volume alone, so no conclusions can be drawn about that single parameter. Third, the high placebo response (an improvement of 2.5 points) is notable, reminding us that a subjective assessment of semen amount is susceptible to expectations and mood.

The practical conclusion is twofold: do not expect TRT to 'increase semen amount', and do not assume it will 'reduce it'. If ejaculate is small, causes must be sought more widely than the hormone.

Despite the above data, many men describe a subjective reduction in volume after starting therapy. From a physiological standpoint there are several possible explanations that are not mutually exclusive. The first is a genuinely smaller share of fluid and cells from the testicles and epididymides — a small fraction, but it may be noticeable if the previous volume was very high. The second is a change in consistency: without sperm, semen can be watery and look like 'less' regardless of its actual volume.

The third and most often overlooked explanation is factors unrelated to therapy that coincide with its start. They include longer or shorter abstinence periods, dehydration, age, chronic prostatitis, prostate enlargement, diabetes, thyroid disease and medications. Particular attention is paid to 5-alpha-reductase inhibitors (finasteride, dutasteride) and bladder-neck relaxing drugs used in benign prostatic hyperplasia (e.g. tamsulosin), which can change ejaculation, including causing retrograde ejaculation, in which semen passes into the bladder. A man who was prescribed both kinds of drugs in the same period will easily attribute the changes to testosterone.

Men who want to preserve fertility during TRT often hear about human chorionic gonadotropin (hCG), which mimics the action of LH and sustains testosterone production in the testicles. The details of hCG use are covered in a separate entry in the knowledge base, and the mechanism and data on testicular shrinkage are described in our article on testicular atrophy. Here we are interested in what hCG does to semen.

What follows for volume? In the hCG group semen parameters, including volume, did not change during treatment, which is consistent with the idea that volume depends on accessory glands maintained by circulating testosterone, not on the testicles. For completeness: other fertility-protection strategies — drugs that raise endogenous testosterone (e.g. clomiphene) or newer short-acting testosterone forms — have no comparable data on volume, and their use is sometimes off-label and should be supervised by a specialist.

If the goal is solely to improve the symptoms of hypogonadism (libido, energy, mood), TRT may be justified and need not fundamentally change ejaculate volume. If the goal is to preserve fertility, TRT without an additional strategy is a risky choice. Distinguishing these two goals is crucial and should come up at the first visit.

Remember the limits of the available data. There are no large randomized trials that measured ejaculate volume as the primary endpoint during TRT; conclusions rest on the physiology of the organs, on indirect data from contraception and fertility research, and on small clinical series. Any individual observation should therefore be verified with a semen analysis rather than relying on impression.

Ejaculate volume and fertility are two separate topics that TRT touches in different ways. For sperm count the effect is large and well documented; for fluid volume it is unclear and probably small. That is why a man considering therapy should talk about parenthood plans, not 'semen amount', and a man who has noticed a change should start with a semen analysis and a medication review, not with a dose modification.