DHT is made when the enzyme 5-alpha-reductase converts testosterone inside tissues such as the prostate, skin and liver. Inside cells it is a more potent activator of the androgen receptor than testosterone itself, and some tissues, such as the prostate, need it to develop and work fully.3
Blood levels are much lower than testosterone, roughly seven to ten times lower in men with normal hormone levels.3 Because most of DHT's action happens inside the tissues that make it, the amount measured in blood is a poor guide to what is going on in, say, the prostate.3
Most men first hear about DHT because of two medicines that block 5-alpha-reductase: finasteride and dutasteride. They are prescribed for an enlarged prostate and, in the case of finasteride, for male pattern hair loss. Knowing what DHT does helps make sense of both their benefits and their side effects, including the modest effects on semen described below.
What does DHT do in men?
Before birth, DHT is essential for forming the external male genitals. Boys born with an inherited 5-alpha-reductase deficiency have markedly low DHT and incompletely formed genitals, yet develop strongly male features at puberty when testosterone surges.1
That classic 1974 finding showed that testosterone and DHT have partly separate jobs.1 In adult men, DHT acts mainly on the prostate, the skin and hair follicles. Reducing DHT in the skin clearly slows male pattern baldness, but the biggest factor in who goes bald is genetic sensitivity of the androgen receptor, not how much DHT is in the blood.3
Do DHT blockers affect semen?
Mildly. In a year-long trial of 99 healthy men, dutasteride 0.5 mg and finasteride 5 mg daily cut blood DHT by 94% and 73% respectively, and caused modest, largely reversible drops in semen measures.2
Total sperm count fell by around 29% to 34% at six months. By one year, semen volume was down about 30% with dutasteride and 15% with finasteride, and motility dipped slightly. Morphology did not change.2 Men planning a family who take one of these medicines may want to discuss timing with their doctor. For more on what drives volume, see how to increase semen volume.
Does testosterone therapy raise DHT, and does it matter?
Testosterone therapy can raise blood DHT modestly. A detailed review concluded that such rises should not be a concern in practice and have not been linked with higher prostate cancer or enlargement risk.3
The review also found no DHT-specific safety signals in long-term studies of DHT gel, even when blood DHT rose around tenfold, though it noted that large long-term trials are still lacking.3 Men on TRT are monitored for prostate health regardless.
Should you worry about your DHT level?
For most men, no. DHT is rarely measured routinely, and blood levels say little about activity inside the tissues. Symptoms such as urinary changes or hair loss are better guides than a number.
DHT is one of several hormones made from testosterone, alongside oestradiol, and it is testosterone itself that doctors measure when checking for deficiency. Human research on supplements sold as DHT blockers or boosters is still developing, so it is worth talking to a GP or pharmacist before trying one. If you notice new urinary symptoms, such as a weak stream or getting up at night to pass urine, see a GP, because the prostate is worth checking in its own right.
Common questions
Does DHT cause hair loss?
DHT plays a role in male pattern baldness, and lowering DHT in the skin slows it. But genetics, especially how sensitive your androgen receptors are, matters more than your blood DHT level.3
Is DHT the same as testosterone?
No. DHT is made from testosterone and is a more potent activator of androgen receptors inside cells, but it circulates at much lower levels.3
Can DHT blockers lower semen volume?
Yes, modestly. In one trial, semen volume fell about 30% with dutasteride and 15% with finasteride after a year, with changes that appeared largely reversible after stopping.2
Read more on this
How to increase semen volume: what actually works
How testosterone changes after 40 (and what actually helps)
Sources
- Imperato-McGinley J, et al. Steroid 5alpha-reductase deficiency in man: an inherited form of male pseudohermaphroditism. Science. 1974;186(4170):1213-1215. PubMed
- Amory JK, et al. The effect of 5alpha-reductase inhibition with dutasteride and finasteride on semen parameters and serum hormones in healthy men. J Clin Endocrinol Metab. 2007;92(5):1659-1665. PubMed
- Swerdloff RS, et al. Dihydrotestosterone: biochemistry, physiology, and clinical implications of elevated blood levels. Endocr Rev. 2017;38(3):220-254. PubMed
Not medical advice. Written by Eric Stephens from the research cited above; not reviewed by a doctor. If something worries you, see a GP.