Dihydrotestosterone (DHT)
5-Alpha-Reductase Physiology: Where DHT Matters vs Where Testosterone Acts Directly
Evidence grade 4 of 5, Strong. Read how the Atlas grades evidence.
The written rationale for this grade is still being prepared.
- FDA
- N/A (endogenous metabolite); 5-ARIs (finasteride, dutasteride) are FDA-approved
Reference only. Not medical advice.
What can go wrong
5-alpha-reductase inhibitors (finasteride, dutasteride) can cause decreased libido, erectile dysfunction, and ejaculatory changes; a subset of men report persistent symptoms after stopping (post-finasteride syndrome), which remains scientifically contested but is taken seriously by regulators. 5-ARIs roughly halve PSA, which must be accounted for in prostate-cancer screening. DHT itself is not something men typically supplement, though topical/transdermal DHT preparations exist outside the US.
This is something to take to a clinician. The Atlas can tell you what is known about dihydrotestosterone (dht) in general. It cannot tell you what is happening in your body, and the difference matters most for exactly the symptoms that bring people to this page.
Dihydrotestosterone is the most potent natural androgen, formed when 5-alpha-reductase removes a double bond from testosterone. DHT binds the androgen receptor with several-fold higher affinity and dissociates more slowly than testosterone, effectively amplifying the androgen signal in specific tissues. The physiology divides cleanly: DHT is the operative androgen in the prostate, the skin and hair follicle, and the external genitalia, whereas testosterone acts DIRECTLY (without conversion) on muscle, the larynx, and via the brain on libido and spermatogenesis. Two 5-alpha-reductase isoenzymes exist, and the rare human 5-AR type-2 deficiency syndrome reveals exactly which traits depend on DHT.
The androgen amplifier. Testosterone does some jobs itself; for others it must first become DHT.
What people take it for
What it is taken for. Approval, where it exists, covers only some of these.
- Prostate
- DHT-driven growth; 5-ARIs shrink the gland in BPH
- Hair
- DHT miniaturizes susceptible scalp follicles; 5-ARIs are used in androgenetic alopecia
- External genitalia
- DHT-dependent development demonstrated by 5-AR deficiency
How it works
5-alpha-reductase (two isoforms, SRD5A1 and SRD5A2) catalyzes the irreversible reduction of testosterone to DHT. Because DHT binds the androgen receptor more tightly and stabilizes the receptor-DNA complex longer, it acts as a tissue-level amplifier in cells that express the enzyme richly, notably the prostate, genital skin, and the dermal papilla of hair follicles. In scalp follicles of genetically susceptible men, DHT miniaturizes hairs (androgenetic alopecia); in the prostate it drives glandular growth, the rationale for 5-AR inhibitors in BPH and the chemoprevention signal in prostate-cancer trials. Crucially, DHT does NOT aromatize to estradiol, so DHT-dominant androgen action carries no estrogenic component.
The 5-AR type-2 deficiency experiment of nature
Imperato-McGinley's studies of 5-alpha-reductase type-2 deficiency (the 'guevedoces' of the Dominican Republic, 1974) are the definitive natural experiment. Affected 46,XY individuals, unable to make DHT, are born with ambiguous or feminized external genitalia DESPITE normal testosterone, proving external genital development is DHT-dependent. Yet at puberty, surging testosterone (acting directly) still drives muscle, voice deepening, and male sexual identity, while the DHT-dependent features (prostate growth, male-pattern hair, facial hair density) remain reduced. This precisely maps the division of labor: T for muscle/voice/libido, DHT for prostate/skin/external genitalia. It also explains why finasteride users keep muscle and (usually) libido while gaining hair, and why a minority report persistent sexual side effects, an actively debated phenomenon (so-called post-finasteride syndrome).
What people get wrong
Often saidDHT is just 'bad testosterone' you want to suppress
ActuallyDHT is essential for normal male external genital development and is a normal androgen. Blanket suppression is appropriate only for specific indications (BPH, hair loss) and carries its own sexual side-effect profile.
Often saidMore 5-alpha-reductase blockade is always safer for the prostate
Actually5-ARI use shrinks the prostate and lowers PSA, but it complicates PSA interpretation and a minority of users report persistent sexual dysfunction; it is a targeted therapy, not a wellness supplement.
Who profits, and who pushes back
Nobody is named here yet, because we have not done that work on this entry. Read that as unfinished. Somebody almost certainly sells this, and somebody almost certainly disputes it. Assume both until we have checked.
What we do not know
- Is post-finasteride syndrome a distinct entity, and what is its true incidence and mechanism?
- How should PSA be reinterpreted in long-term 5-ARI users for cancer detection?
- Does scalp-targeted vs systemic 5-AR inhibition meaningfully change the side-effect ratio?
At a glance
- AR affinity
- DHT binds AR ~2-3x more avidly than T, dissociates ~5x slower
- Isoenzymes
- Type 1 (skin, liver), Type 2 (prostate, genital skin, hair follicle)
- Finasteride
- Blocks type 2; dutasteride blocks both
- Cannot aromatize
- DHT is NOT converted to estrogen
What this entry does not yet cover
What follows is unfinished work on our side, not a finding about Dihydrotestosterone (DHT). A short entry is not a safe entry.
- Timeline. We have not built the dated record of research and regulatory events.
- Cost and market. We have not documented what it sells for or who sells it.
- Supply chain. We have not mapped where it is made.
- Who uses it. We have not documented the user groups.
- What could change. No forward-looking summary yet.
- How it compares. We have not set it against the alternatives.
- Children and teenagers. We have not checked what is known about younger people.
- Where we land. We have not taken a position on this yet.
Sources
The studies below are named and described, but not linked. You cannot open them from here and check our reading against them, which means this page is our summary of the literature rather than a document you can verify. Weigh it accordingly until the links exist.
The studies that matter
Imperato-McGinley 5-AR deficiency1974
'Guevedoces' cohort: DHT required for normal external genital development; T sufficient for puberty's muscle/voice changes
PCPT (finasteride chemoprevention)2003
Finasteride reduced overall prostate-cancer detection but raised a high-grade signal later attributed largely to detection bias
Finasteride/dutasteride alopecia trials1998-2006
5-AR inhibition lowers scalp DHT and improves hair counts in androgenetic alopecia