What DHT is
Dihydrotestosterone (DHT) is the most potent natural androgen at the androgen receptor. It's produced from testosterone by the enzyme 5α-reductase, which removes a 4,5 double bond on the steroid A-ring.
Why DHT is more potent
Compared to testosterone, DHT:
- Binds androgen receptor with 3-5× higher affinity
- Dissociates more slowly
- Stabilizes the active receptor conformation more effectively
- Is not aromatized to estrogen (no estradiol conversion possible)
The result: DHT-dominant tissues experience stronger androgen signaling than T-dominant tissues at the same total androgen exposure.
Type 1 vs Type 2
Two 5α-reductase isozymes:
- Type 1 (SRD5A1), primarily skin, sebaceous glands, liver, brain
- Type 2 (SRD5A2), primarily prostate, seminal vesicles, hair follicles, external genitalia, liver
The two isozymes have different substrate preferences and tissue distributions, with type 2 being the more clinically relevant for prostate and hair issues.
Where DHT dominates
- Prostate (BPH and male pattern fertility)
- Scalp hair follicles (male pattern hair loss)
- External genitalia (development)
- Skin (sebum production, body hair)
In these tissues, DHT signaling is what drives the androgen effect.
5α-reductase inhibitors
Pharmacological options:
- Finasteride, blocks type 2 primarily; reduces DHT ~70%
- Dutasteride, blocks both types; reduces DHT ~95%
Approved uses:
- Benign prostatic hyperplasia (reduces prostate size, improves urinary symptoms)
- Male pattern hair loss (preserves and partially regrows hair)
Trade-offs of inhibition
Side effects in some patients:
- Sexual: reduced libido, erectile dysfunction, ejaculation issues
- Mood: depression, anxiety
- Cognitive: brain fog
- "Post-finasteride syndrome", persistent symptoms after stopping
Most users tolerate the medications well. A minority experiences significant side effects, sometimes persistent. The trade-off reflects DHT's roles beyond hair and prostate, it has effects in brain, sexual function, and other domains.
On TRT considerations
Patients on TRT may experience:
- Increased DHT (proportional to T increase)
- Accelerated male pattern hair loss in genetically susceptible men
- Variable prostate effects (TRT does not cause prostate cancer per TRAVERSE; PSA monitoring continues)
For TRT patients with significant hair concerns, finasteride combination is sometimes considered, with awareness of side effect profile.
The clinical insight: DHT is essential for normal androgen biology in some tissues. Inhibiting it has benefits (hair, prostate) but trade-offs (sexual, mood, cognitive). Patient-specific decision balancing benefits and risks.
Bottom line
5α-reductase converts testosterone to DHT, the more potent androgen. Two isozymes with different distributions. Inhibitors useful for BPH and hair loss but with potential side effects reflecting DHT's broader physiologic roles. Patient-specific decisions about use.