Men on TRT (testosterone replacement therapy) should always have good levels of DHT (dihydrotestosterone), right? After all, we get our DHT from testosterone and so men with good levels of testosterone from TRT should have good levels of DHT. And DHT is very important, since it is responsible for a good portion of our libido.
However, men on injections of testosteorne cypionate or enanthate can actually end up with levels of DHT that are not high enough to sufficiently boost libido. Usually this is not the case, but it can happen. There is an enzyme (5-alpha reductase) that converts your testosterone into DHT and so the amount of DHT that you end up with is dependent on this metabolic process, and it is quite unpredictable.
So, if you are on injections, and end up with a) low libido and b) DHT levels in the lower part of the lab range for men, what do you do? Do you switch to some other type of testosterone therapy, i.e. another delivery system? You could, of course, switch to the topicals / transdermals. For example, Androgel works very well for some men. If you need a less expensive alternative or, if Androgel does not work for you, you can also try this: Compounded Testosterone Transdermals. (Compounded testosterone has a huge advantage: it can be written for any strength.)
Transdermal testosterone, because it is rubbed into the skin, has a very high conversion rate to DHT. From what I have seen on the Peak Testosterone Forum, men using transdermals will usually end up with DHT well over the top of the lab range, i.e. "supraphysiological." Supraphyiological means that your DHT is actually at unnatrually high levels that simply don't occur in healthy, young men. I would add, actually, that DHT very often ends up 2-4 times the top of the lab range actually, and this is one of the things that I personally don't like about transdermals. I just personally feel uncomfortable driving hormones to very high levels, and with DHT you could potentially accelerate male pattern baldness and/or cause prostate issues, so you want to stay within the lab range and try to hit the targets you and your (hopefullly knowledgeable) doctor set.
So is there a better solution out there? One of our senior forum members (JustAskin) alerted me to a clever solution that takes advantage of this property of transdermals. JustAskin's TRT physician, by the way, is the legendary Dr. Shippen, who has been a pioneer and apostle of almost all the good T-raising protocols that savvy doctors use today. Note that JustAskin's TRT protocol was testosterone cypionate injections, but he still had a low libido and DHT on the low side.
SOLUTION: Dr. Shippen recommended that he use a transdermal compounded testosterone once every seven days to boost DHT in conjunction with his cypionate injections. They found that his DHT actually went too high with this protocol and so then they switched it to every two weeks and that worked very well. It is amazing that the effect of the transdermal cream lasts this long but that is the case. Just Askin commented on this solution here:
"I found thru many labs ran that my libido is like in my twenties when my DHT is around 105. Caution: If you take 2 Grams of L-Citrulline when your libido is high, it will get so hard it actually hurts." 
By the way, I will add that JustAskin is in his 60's and so this turned back the clock about four decades! No one can promise that will happen for any given individual - JustAskin's arteries are clearly in decent shape for example - but I'm just passing along information as to what has worked for some men on the Peak Testosterone Forum.