You have to define what you mean by regrowth because no one ever defines this term or contrasts it with the terms "growth" or "improvement". I think that AA's, including reductase inhibitors can halt hair loss fairly effectively and probably, few debate this. As regrowth agents, they are likely to work best for the very young.
Once follicles go completely dormant, however, I don't think that there is good evidence that AA's cause regrowth or that they awaken dormant follicles. This appears to be what estrogens do, however. This is why virtually all of the impressive "recoveries" are by either transgender females or XY's who don't attempt to avoid feminization like
@bridgeburn on the hormonal life thread.
It's not safe to take AA's other than reductase inhibitors without estrogen, however, for longer than a handful of months. My feeling is that the AA's (mainly spironolactone, CPA and bicalutamide) spoof regrowth in some but it doesn't last and it is probably due to some lengthening of anagen more so than due to the awakening of dormant follicles but we don't know. I harp constantly for the people using AA's without estrogen to post pics and none of them ever do.