When I took it, I found it made me a helluva lot more horny, and I had a super-short fuse, I'd get pissed at people quite quickly. And I broke out with some mild acne a bit.
On a factual side, it actually *could have* increased my free testosterone levels; I had them checked before taking trib, and during. The levels were substantially higher during the time I was taking trib, but still within the normal ranges. Now, at this time, I was also lifting the heavest poundage I ever had.
Does it work? Sure, anecdotally.
The only real study I've ever found on tribulus found it "had pro-erectile activity", but didn't have any anabolic qualities. Heh.
Needless to say I don't waste my money on it anymore.