While it deceases serum DHT, I believe its effect is by stopping the intracellular conversion at the scalp.
I also think this is (one reason) why some men may have sides.
Hairloss is not necessarily dependent on serum DHT, but DHT sensitive scalp. If someone had low-ish DHT to begin with, but a very DHT sensitive scalp, they might still lose hair. If this person also took finasteride, while they might lower hair loss, they might reduce their serum DHT to almost nonexistent levels.
This is why I cannot imagine a hair transplant doc/derm rxing finasteride without first running baseline hormone labs.
My serum DHT ON finasteride is just below top of range, I have no sides. My baseline DHT was over top of range, even before TRT.
This is actually a really, really good point. Using DHT levels and scalp sensitivity as two independent factors yields the following possibilities:
1) Naturally high DHT; scalp very sensitive to DHT (highest risk of hairloss)
2) Naturally low DHT; scalp very sensitive to DHT (moderate risk of hairloss)
3) Naturally high DHT; scalp not sensitive to DHT (moderate risk of hairloss)
4) Naturally low DHT; scalp not sensitive to DHT (lowest risk of hairloss)
Obviously, there is room for someone to fall between those extremes. Nevertheless, in light of the above, men in the first and third categories would be ideal candidates for finasteride (assuming that finasteride's only effect is to lower DHT). The "best responders" to finasteride are probably men in the third category, and it is tempting to think that Lou is an example of one. Categories two and four should probably avoid it altogether.
Another factor may be pre-existing estrogen levels, Finasteride raises estrogen levels in two interrelated ways: The first is that, by bottle-necking DHT conversion, it leaves more T available for aromatase converstion to E2. Second, because DHT itself is an aromatase inhibitor, there is actually more aromatase available to convert the T to E2. The result is that finasteride will almost certainly result in higher E2 levels. Thus, finasteride may be contradindicated for a man who already has high E2 levels.
I suspect that my DHT levels are naturally quite high, based on the other androgenic characteristics I have (deep voice, significant body hair, etc.). I also have very, very low E2. My E2 fluctuates between 7 and 13 with a TT of 720-750. I wouldn't be surprised if I have super high DHT levels that is suppressing my E2, causing hairloss, etc. I suspect, too, that based on the early onset of my hairloss, that I have a fairly sensitive scalp. I would suspect that I am in the first category and could possibly use finasteride without negative effects; a serum DHT test could confirm.
On the other hand, this is all just a theory. One troubling aspect is the reports of men who have diminished masculinity even after dropping finasteride and whose DHT levels apparently recover to pre-finasteride levels. This suggests that finasteride is doing something other than simply lowering DHT and that whatever that something is may be the real culprit.
This is also to say nothing of the fact that even if one has naturally very high DHT and are still within range even on finasteride, you have lost the "gift" of having naturally high DHT. It would be like telling a man whose TT is 1,200 that he will still be in range if he took a drug that dropped his TT to 800. He may still feel well relative to others, but he would be giving up something relative to himself. So it is with naturally high DHT levels.
To summarize: Anyone considering finasteride should get DHT checked. if it is mid-range or lower, I'd say finasteride is suicide. If it is at the top of the range or over, it might be an option.
