To say herbs don;t have an effect on the body because they're natural is like saying food doesn't have an effect on the body because it's natural.
Tribulus increases LH is SOME people. It can also raise estrogen, which in some cases can actually increase libido. It never did much for me. Whatever it claims to do for libido can be achieved much better with avenacosides. And the increase in LH can be achieved much better with Fadogia Agrestis.
Tribulus, in my opinion, though not inert, is essentially worthless since there are better options.