My first RE recommended I try it for at least three months. I was not doing IVF or any fertility treatments, just TTC naturally, but he thought it would help improve my egg quality. He never tested my levels, but just told me to take 75 mg for three months. I didn't even last on it for two. I had side effects from it, the worst being that it made my cycle irregular and I didn't need any assistance with that.
After talking with my RE about my cycle irregularity, he said, oh yes, DHEA can do that.
Some people swear by it, but the severity of the side effects weren't worth it for me and my levels were never tested and he didn't think it was necessary to do do.