What brand do you use? I've tried only Ultimate Nutrition's Tribulus Terrestris (capsules 750 mg with 45% saponins). As far as I can see, people usually don't have problems with Twinlab's Trib. and Bulgarian Sopharma Tribestan, but I didn't see anyone say positive things about Ultimate Nutrition's Tribulus.
Well, according to that Bulgarian study (the only one about this herb), Tribulus increases lutenizing hormone, thereby forcing your body to increase production of its own testosterone. Allegedly, that's how it works. Lutenizing hormone by itself wouldn't be able to do anything in terms of strength, endurance, libido etc. The problem is that increased LH can increase both estrogen and testosterone, which obviously doesn't sound good.
Either way, if Tribulus really affects testosterone level, in theory you could end up with imbalance in hormone levels and their natural production (this is just my conclusion on the basis of what I've read so far). I just hope that the changes are reversible, that's why I posted the original message, hoping that someone who had his libido down as a result from using Tribulus would say whether it got back up to normal or not.
I've found these messages in the Google's newsgroups archive, you might want to check them out:
http://groups.google.com/groups?hl=en&lr=&ie=UTF-8&
oe=UTF8&safe=off&s...
