Your body produces the greatest portion of it's testosterone in the testicles, but a small amount is produced in the liver. The liver also produces a conversion enzyme called 5-alpha-reductase or "5Ar" which breaks testosterone down into components for bodily utilization.
All androgenic effects of testosterone including maintenance of genital size and function come from DHT not from testosterone in it's original form.
DHT has been available in many forms for many years. There are several injectables and now a gel. DHT is relatively innefective because it has a very short active life in the body when it is exogenous (produced outside the body)
The problems with DHT are many and new research is taking place in this area. It was once thought that DHT was some evil and non necessary thing. Some new research is finding out that maybe current thoughts are wrong.
One example of new research is that while it was asumed that DHT was what caused prostatic enlargement in males as they aged, some new data is finding that maybe this is exactly the opposite of what the real facts are. The problem causing prostatic enlargement under some new data may be related to other hormonal factors. In some cases males with enlarged prostates were given DHT and the prostate glands reduced in size instead of more enlargment.
IF one is genetically predisposted to male-pattern-baldness then DHT can accelerate the process in some men.
DHT blockers can do a great deal of harm and though killing most dht conversion can shrink a prostate if the level is brought down enough, the same dosage can cause many other problems including E.D., loss of body hair, and blood platelet abnormalities. A chance worth taking if you've got a PSA heading for the stratosphere, but not to be used under any other circumstances.
The real hoot is that in a small percentage of men DHT blockers (Proscar//Propecia) cause the "pituitary axis" (your control mechanism that regulates all hormone production) to go nuts and the testicles are sent into "warp drive" producing more and more testosterone trying to get the DHT levels to normalize in the body. When these men are taken off the DHT blockers they have MAJOR problems including warp speed prostate enlargment to sizes far more of a problem than before they were ever given the drug.