On the Peak Testosterone Forum I see certain men's health solutions that have a pretty solid track record. HRT (TRT) does pretty well with a good protocol and on the erectile side, things like pomegranate juice and Citrulline have a decent batting average. DHEA is brand new, but we now have several men who have recently experimented with it with some short term successes at least. For example, look at what this man wrote:
"Before that i was experimenting with 50mgs of DHEA, after a week or two, I noticed morning erections, that were rock hard, the last time i had this was when i was a teenager." 
And it also helped out this guy who was on HCG Monotherapy in several ways:
"I started on 50mg DHEA daily about a week ago and I think it's helped my mood and libido considerably. I am on HCG mono and my T levels look great, but I needed some additional help. My DHEA was in the low 200s so I thought I'd give it a try and I can say I'm actually thinking it's working." 
Just how does DHEA work its magic in some men? Well, one thing that we can say is that it is NOT from increasing total testosterone. Multiple studies in men - it definitely can raise T and DHT in women! - have shown no effect in total testosterone and this is what we will cover below. We will also look at what DHEA does to free testosterone.
NOTE: If you are interested in whether or not testosterone therapy (HTR / TRT) impacts DHEA, skip to the bottom of this page.
a) 50 mg in Men Aged 40-70. According to this study, some change in IGF-1 occurred, but none in testosterone.  This dosage is kind of the standard dosage that I see most men taking on The Peak Testosterone Forum with 25-100 mg being the range.
b) 100 mg in Men Aged 55-70. This small study had a six month study period and found that there was difference in either testosterone or DHT in the men. 
c) ~600 mg in HIV Positive Men. Probably the ultimate verification that supplemental DHEA does not change total testosterone came from a study of HIV positive men where a very large dosage (600 ng/dl) was administered on a daily basis. 
1. Boosting Free Testosterone When Combined With Intense Exercise. Now some of you may know that DHEA can be a precursor to testosterone. So you may be thinking, "Aha! I know why DHEA sometimes does these things: it's boosting testosterone!" However,that typically is not the case, at least in terms of total testosterone. Many studies in men have shown no significant change in total testosterone. Plus, if DHEA routinely increased total testosterone, every bodybuilder on the planet would be taking it.
While it does not appear to consistently boost total testosterone, it may actually boost free testosterone quite significantly if combined with HIIT in some men. See my page How to Increase Testosterone Naturally for the study. As a verification, this same study showed no significant difference in total testosterone levels - only free.
2. Raising Levels Decreased by HRT (Testosterone Therapy). I have not seen proof of this, but one of the well-known online HRT physicians, has stated that HRT generally lowers DHEA levels. We saw this in one of our own guys whose DHEA levels on HRT were about 500 and then rose to 600 when he quit.  For this reason, some HRT docs and clinics recommend supplemental DHEA.
3. Improvement in Erectile Dysfunction. One study showed that 50 mg of DHEA improved all five domains of the IIEF test, one of the standard measures of erectile dysfunction used by researchers.  As a side note, no changes in testosterone were noted as mentioned about. (No increase in PSA or prolactin was noted either.)
4. Brain Booster. In my opinion, HRT works not because it can (sometimes) improve erectile function or restore morning erections, but instead because it is such a brain booster for hypogonadal men. For a man who has low testosterone, Testosterone Can Restore Brain Dopamine and increase brain-benefitting estradiol and DHT levels as well. Therefore, libido and mood usually increase on a well-done HRT program. Depression scores improve. And even mental performance can improve - working and verbal memory for example. Basically, this is not always the case, but usually in my opinion testosterone is a great "brain tonic" for a man that is deficient.
Now let's go back to DHEA. Does it exert similar brain-boosting characteristics? The answer is that it probably does not for most men, simply because there are quite a few studies who found that in men no increased libido, mood or memory. (Women do a little better in the studies.) However, there was one study that found that it "was associated with a remarkable increase in perceived physical and psychological well-being for both men (67%) and women (84%)."  Unfortunately, there was no increase in libido. Like most of the studies, the participants were give 50 mg per day. The bottom line is that some men, for reasons unknown, may get a boost in well-being, mood and the like, but don't expect it. This brain boost may be responsible for some of the good reports I am getting.
5. Sleep Aid. DHEA can lower cortisol and is considered a "stress tonic" by some. Perhaps for this reason, DHEA seems to help with sleep in the sense that it increases REM sleep.  Interestingly enough, morning erections generally occur during the REM sleep phase, so perhaps this explains why the man above enjoyed improved morning erections? (A very large dose, 500 mg, was given in this study and it was on healthy young men. So more study work needs to be done in this area.)
6. Cortisol Reduction. DHEA can lower cortisol as well in some men. Generally, this is not the case though according to a number of studies
CAUTION: DHEA should not be given in my opinion if you are not low in DHEA. It should also not be given in higher dosages. See my page Potential DHEA Dangers for more information. While DHEA levels plummet with aging, it is important to get a DHEA read before. You can pull your DHEA inexpensively here: Testosterone Labs.
Above I documented the studies that show that DHEA does not significantly increase total testosterone on average but likely does increase free testosterone in many men. But what about the other way around? What if a man significantly boosts his testosterone through HRT (TRT)? Will that raise or lower his DHEA?
Unfortunately, my answer to that question is anecdotal: there are several knowledgeable HRT physicians who have stated that decreased DHEA is a common side effect in the medium and long term testosterone therapy. The reason given for this is that testosterone tends to shut down the body's HPA (hypothalamus-pituitary-adrenal) axis, and the theory is that this "shutdown" can leave some men with lower DHEA.
Can I prove this or back it with some references from the medical journals? No, I cannot. However, I can tell you that my DHEA was every low after being on testosterone cypionate for a couple of years. My DHEA-S was right around 100 ug/dl last year (2014) and a typical range for a man my age would be about 109-208 (25th, 75th percentile). 
On a practical level, it would be prudent for men on TRT to measure their DHEA-S before and after TRT. For more information on DHEA, see my Index Page on DHEA.
3) The Journal of Clinical Endocrinology & Metabolism, Published Online: July 01, 2013, 78(6), "Effects of replacement dose of dehydroepiandrosterone in men and women of advancing age."
4) Urology, Mar 1999, 53(3):590 594, "Dehydroepiandrosterone in the treatment of erectile dysfunction: a prospective, double-blind, randomized, placebo-controlled study"
6) American Journal of Physiology - Endocrinology and Metabolism, 1 Jan 1995, 268(1): "DHEA administration increases rapid eye movement sleep and EEG power in the sigma frequency range"
7) ) Metabolism Clinical and Experimental, 2006, 55:858-870, "Endocrine effects of oral dehydroepiandrosterone in men with HIV infection: a prospective, randomized, double-blind, placedbo-controlled trial"
8) Clin Endocrinology, 1998, 49:421-432, "The effect of six months treatment with a 100 mg daily dose of dehydroepiandrosterone (DHEA) on circulating sex steroids, body composition and muscle strength in age advanced men and women"
9) Journal of Andrology, Nov-Dec 2008, 29(6):610 617, "Reference Ranges for Serum Dehydroepiandrosterone Sulfate and Testosterone in Adult Men"