Well I will go away and do some research but as far as I am aware there are no side effects of Tribilius taking. Mind you I take the recommended dosage.
I use the Redback one, which is Aust. made. They also do powders and other stuff.
I use the Tribilius for stamina in running (and not erection problems ). It has the effect of purportedly being a libido enchancer and mild aphrodesiac. The fellow I purchased it from indictaed that if you are using it as a "herbal viagra" or sexual dsyfunction, people under 35-40 will not notice much difference. It's main benefit is for people over 40 who have erectile or low sperm count issues.
However I have found a slight increase in my libido (not that it gets much use ). Stamina wise can't really tell - I think it mainly used as a muscle building herb rather than stamina. I also take it as I believe it increase the metabolism (but again not by much).
Interesting L-Glutamine is also used for sexual enhancement - viagra is generally derived from L-Glutamine in regards to the nitric oxide effect. I have found the Glutamine helpful in recovery sessions, particular when combined with creatine.
Edit: Forgot to add re: the above topic - Tribilius can come by itself (moderately rare), with some zinc (slightly more common) and with zinc, horny goat weed and one or two other herbs (common). The bodybuilders tend to try and go for the first two, but most brands seem to have the last combo. I tried Bio-Organics which is No.2 (a bit of zinc) - it seemed okay. Reback is like No.3 with the other stuff.