You may have noticed that erectile dysfunction related human studies for this supplement are lacking. Well, all I can say is all those rats couldn't have been that wrong. Steven Lamm, . in his excellent book, The Hardness Factor , uses it in his practice and says that many of his patients swear by it. He performed a (non peer-reviewed) HGW study on 38 men. 25 were healthy men and 13 were taking Viagra. About two thirds of the healthy men and about half of the men using Viagra responded positively to the Horny Goat Weed. Of course, this is not a rigorous study, since the placebo effect was not taken into account, but it's a good sign nonetheless.
Total testosterone goes down by about 1-2% per year , starting sometime in your 30s, and bioavailable testosterone decreases by about 2-3% a year. Those numbers can be pretty misleading though. Men approaching middle age tend to exercise a lot less, and eat a lot worse. So nobody really knows what a “natural” decline in testosterone looks like, on a population-wide basis. It’s kind of like saying muscle mass decreases 1-2% a year once you hit middle age … that decrease can have a lot to do with more time spent on work and family, and less time spent trying to get ripped to attract a partner (among other reasons, of course).