What I do know is that minoxidil definitely makes eyebrows grow thicker and coarser, at least for me and several others here on this forum. And no, I don't apply the minoxidil ON the eyebrows of course, but just from applying it on the scalp, there is some that somehow travels through the vascular system and makes its way to the eyebrows.
Actually, I think the eyebrow thickening has been less dramatic than the beard growth side effect I have had from minoxidil. My beard is definitely coming in faster... and those little hairs on the back of the neck that the hairstylist usually trims off.. those hairs grow amazingly fast. I actually have to shave them off between hairstylist visits to keep from looking like orangatang man.
As for the spironolactone, no, I don't think that spironolactone in and of itself has an effect on a normal person's eyebrow. BUT, for those of us as myself who have noticed thicker eyebrow growth as a function of ageing (that happens as you get older) I BELIEVE that spironolactone helps keep them thin. I know that the same DHT that causes us baldies to go bald has an inverse effect on body hair. That is, as we get older, DHT triggers scalp follicles to miniaturize, and causes body hair follicles to thicken... this starts with the development of a beard and pubies during puberty and then slowly continues to chest hair growth, and then to the dreaded back hair growth and thick eyebrows.
I read a post in a different forum that was cited here that was made by a man who could not grow a beard and had no body hair. He went to a Doctor and was told that his testosterone levels were ok, but, his body was not synthesizing enough DHT from the testosterone to promote the kind of hair growth that is expected in a man. He kind of had the opposite problem as we had, but far from being a good thing one can only imagine what kind of other problems this fellow must be suffering from if the puberty-inducing DHT was in chronically low levels in his body.
So, I decided to do an experiment and see if spironolactone would help thin out my ageing eyebrows. And I can tell you that for me, at least it definitely has done so. I figured that if transvestites take it orally (no pun intended) and it helps them rid themselves of male body hair, applying it topically to the eyebrows might get them back under control. And it has definitely WORKED for me. I used to trim them every week. Now, only a stray one here and there for the past several weeks. It took a while, four months or so, but it worked for me. Of course, on the down side I know have this uncontrollable urge to wear fishnet stockings and take it up the ***, but at least my eyebrows are under control. Just kidding. That was a joke.
Hope this helps clarify. Gardener