It goes by many names – Epimedium brevicornum (the plant), icariin (the active chemical), Horny Goat Weed (the commercially available product). I have purchased this from Physicians Formulas and found that it is like a weak Viagra. Of course, with herbs, you never know what you are getting – there is no FDA regulation or quality standards with herbal products – but there is definitely a weak effect.

Now there is a study from the Department of Pharmacological Sciences, University of Milan, which says that altering icariin, the active chemical in Epimedium, can produce a chemical that is as active as Viagra. Here is the link to the recently published study: (CLICK HERE).
One of the authors on the study also showed, in another study, that red wine and the extracts from grape skin inhibit PDE5, the same enzyme that Viagra inhibits. For study: (CLICK HERE).Please note: I have found a recent study that shows that combining HGW with Viagra (and presumably other PDE5Is) is not a good idea, and that HGW can reduce levels of Viagra by up to 60%! See my post on this.

Here is a link to that study:
http://www.mdpi.com/1420-3049/18/6/7323