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Ashwagandha KSM-66 vs Tribulus Terrestris

A scientifically based look at Tribulus and Ashwagandha's effect on testosterone

Tribulus Terrestris

Tribulus Terrestris is easily the most popular herb used as a natural testosterone booster, but does the research back its use?  When anecdotal evidence is ignored and Tribulus is put under real scientific scrutiny, it consistently proves to be ineffective.  It has been shown to have  no effect on testosterone in human studies. But what about all the claims of its ability to supercharge muscle growth?  Again, Tribulus Terrestris when compared to placebo, shows no increase in lean muscle mass.

So Why All Misconceptions?

Some evidence supports the claim that Tribulus increases libido and sexual performance, which is often the goal when trying to boost testosterone.  And when this happens individuals typically incorrectly conclude increased testosterone is the reason for it.  So in summary, if your goal is building muscle and increasing testosterone there is no reason to believe Tribulus will benefit you.  But if you are trying to improve your sex drive it may be a viable option.


An 8-week, randomized, double-blind, placebo-controlled  clinical study, with 57 young male subjects (18-50 years old) was carried out to determine the effect of Ashwagandha on serum testosterone levels, muscle mass, and strength.  Below is a summary of the study's findings.

Significant increase in testosterone (Placebo: +18.0 ng/dL vs. Ashwagandha +96.2 ng/dL)

• Average of 43.2 lb. individual increase in bench press over the placebo group

• Significant increase in muscle size at the arms (Placebo: +5.3 cm vs. Ashwagandha: +8.6 cm)

• Significant reduction of exercise-induced muscle damage as indicated by the stabilization of serum creatine kinase

• Significant decrease in body fat percentage (Placebo: -1.5% vs. Ashwagandha: -3.5%)

Ashwagandha is thought to produce these results primarily from its effect on cortisol. One study  showed a 27.9% decrease in cortisol after 60 days of supplementing 300 mg/day.  Reducing this stress hormone will increase testosterone and the ability to build muscle, it can also reduce anxiety and stress.