It's the only prohormone that's still legal. DHEA, when it was declassified as a Schedule II (or III) drug in the mid-90s, it was marketed at the next best thing to steroids. That opened the door, of course, for androstenedione and its more potential big brother, androstendiol.
Then, you had norandrostendione and norandrostendiol, the precursors for nandrolone.
They all got banned except for DHEA.
Back in the day, it was recommended that you take 200 to 250 mg of DHEA to get any decent effects from it. I don't know if that's changed since then.