"In otherwise healthy males, testosterone is not influenced with supplementation of tribulus terrestris. There may be an increase in infertile men, but this is weak."
and
"A study in fertile boars with combination therapy of tribulus terrestris, Eurycoma Longifolia Jack and Leuzea carthamoides noted that 11mg/kg oral administration (correlating to a 750mg oral dose for a 70kg human) increased mounting behaviour by 20% and increase seminal volume; higher doses (42mg/kg and 110mg/kg) were unaffective.[80]
Various other animal models confirm aphrodisiac effects, including the lyophilized extract dried fruits at 50mg/kg and 100mg/kg in sexually sluggish male rats which noted dose-dependent increases in all parameters of sexuality and penile function increasing with prolonged administration.[59] Intake of tribulus at lower doses of 2.5, 5, and 10mg/kg for a period of 8 weeks was associated with decreases in the latency of mounting, intromission, and ejaculation while improving mounting and intromission frequency; with 5mg/kg and 10mg/kg being of equal potency[35] and in castrated rats Tribulus appears to be slightly less effective at 5mg/kg than were biweekly injections of testosterone cypionate at inducing aphrodisia, but both groups were lesser than an uncastrated control[84] while another study comparing Tribulus Terrestris against Sildenafil Citrate (Viagra) in sexually normal rats at doses of 100mg/kg bodyweight and 0.71mg/kg, respectively, found that there were no significant differences between both groups, as both were more effective than control at inducing aphrodisia with similar efficacy.[60]
In men with low sperm count, supplementation of 6g tribulus root is associated with a significantly greater improvement in sexual health (assessed by survey) by 49.38% which was greater than placebo (27.80%).[67]"
