On this page, I will be talking about the standard DHEA dosages that I see out there. However, even discussing the subject makes some assumptions in my mind. First of all, I don't think anyone should supplement that is not actually low in DHEA-S. Furthermore, I believe that this kind of "protocol" should be followed:
a) Talk to a doc or LEF, naturopath or Life Extension Foundation and find out if you have any contraindications. (High PSA, arrhythmia, etc.) Read my page on DHEA Dangers.
b) Get a DHEA-S blood draw and, if low, proceed to b.
c) Discuss with a doc or LEF, naturopath or Life Extension Foundation an appropriate dosage. Of course, I recommend reading below
c) Find your target DHEA-S levels. I have seen docs and the LEF generally target a range of 350-500 ug/dl approximately.
d) Re-measure after a few weeks and verify you have hit your target levels.
CAUTION: My labs were 108 ug/dl, which is very low, and this is the sole reason that I tried it. Again, you do not want to even consider taking DHEA in my opinion unless you are low in DHEA-S and you do not want to go too high in DHEA-S after you begin taking DHEA either. Set a target with your physician or naturopath. From what I have seen, usually the upper mid range of DHEA-S is what is targeted and where men often feel best.
1. Ray Peat (~4 mg daily). Ray Peat, a respected blogger with a Ph. D. in Biology wrote:
"Young people produce about 12 to 15 milligrams of DHEA per day, and that amount decreases by about 2 mg. per day for every decade after the age of 30. This is one of the reasons that young people eat more without getting fat, and tolerate cold weather better: DHEA, like the thyroid hormone, increases our heat production and ability to burn calories. At the age of 50, about 4 mg of DHEA per day will usually restore the level of DHEA in the blood to a youthful level. It is important to avoid taking more than needed, since some people (especially if they are deficient in progesterone, pregnenolone, or thyroid) can turn the excess into estrogen or testosterone, and large amounts of those sex hormones can disturb the function of the thymus gland and the liver." 
His comment about 4 mg restoring youthful levels does not mesh with that of LEF, where around 25 mg is used to get men back to youthful levels. Studies that I have seen also mention a higher dosage to get to youthful levels. As I always say: measure yourself and see if you are hitting your target levels. You can do that with these cheap Self-Testing Testosterone Labs.
2. Dr Shames (5-10 mg daily). Dr. Shames is one of the pioneering thyroid and adrenal fatigue physicians. He writes in his book that it is a "potent medication" that should be limited in his opinion to 5-10 mg daily. 
CAUTION: I always recommend, when it comes to hormones, working with a knowledgeable physician, naturopath or organization such as Life Extenson Foundation. Also, some countries do not allow over the counter purchases of DHEA.
3. LEF (15-50 mg daily). To find the dosage appropriate for me, I called Life Extension Foundation and they recommended 25 mg for a man on testosterone therapy like myself. However, their page says that one may need between 15 and 50 mg in order to achieve target levels of DHEA-S. What are these target levels? According to their web site as of this writing, the stated goal for adult men is to keep DHEAS levels between 350 and 500 ug/dl.  This is what I call a "replacement philosophy," where the goal is simply to restore a give hormone to youthful levels. The contrast to this is going "supraphysiological," i.e. raising hormones past what is normal and natural. This often leads to problems in my opinion whether you are talking about testosterone, estradiol, DHEA, melatonin, etc.
One of the moderators on the Peak Testosterone Forum provided an example of this when he took 25 mg of DHEA and yet it only boosted his levels of DHEA-S to ~220 ug/dl. 
4. IGF-1 (25 mg). On my page DHEA and IGF-1, I make a case that 25 mg should probably be your upper limit on DHEA, in order to avoid raising your IGF-1 levels too much. (Not everyone reacts the same to a given dosage, so the best thing is to measure your IGF-1 before and after using on of these Hormone Labs in my opinion.)
5. Well Known TRT Doctors (25 mg daily). Dr. Shippen is one of the early pioneers of testosterone therapy and seems to be well-respected by his patients. (I have no affiliation.) He wrote the TRT classic The Testosterone Syndrome years ago that was clearly ahead of its day. According to one of our senior posters on testosterone therapy, Dr. Shippen prescribed 25 mg of oral DHEA per day. Dr. Shippen prefers this brand. Like me, this man is on HRT (testosterone therapy) that includes a combination of testosterone cypionate and daily HCG. Does this mean that Dr. Shippen always recommends 25 mg? Of course not. I am sure he tailors based on your preexisting DHEA-S levels, whether you are on TRT and a number of other factors, i.e. you'd have to set up an appointment to verify. 
In addition, you can read in my post on How DHEA and Pregnenalone Cured My Anxiety how Dr. Justin Saya put me on a similar dosage of 25 mg of DHEA per day (oral before bed). Again, you would have to call Dr. Saya and make an appt to find his dosage for you inidividually.
6.Diabetes and Prediabetes (25-50 mg daily). This is an involved subject as the studies are mixed. In my opinion, the data overall suggests that men struggling with blood sugar issues and high cholesterol can improve insulin sensitivity and normalize blood sugar levels with reasonable dosages of DHEA. Of course, if you are diabetic in particular, it is critical to talk to your doctor first before making any changes.
7. Mood, Depression, Anxiety and Cognition (50 mg). Dosages in the successful studies for these conditions tend to be 50 mg from what I have seen. For example, one study of middle-aged and senior men and women 40-70 years found that 50 mg "was associated with a remarkable increase in perceived physical and psychological well-being for both men (67%) and women (84%) ." 
4) Feeling Fat, Fuzzy or Frazzled, by Dr. Shames, p. 163
5) J Clin Endocrinol Metab, 1994 Jun, 78(6):1360-7, "Effects of replacement dose of dehydroepiandrosterone in men and women of advancing age"