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Free Testosterone

Free testosterone is a measurement of testosterone that is not bound to SHBG, and is thought to be more reflective of the effects of testosterone than a basic blood measurement of testosterone.

Human Effect Matrix

The Human Effect Matrix looks at human studies (it excludes animal and in vitro studies) to tell you what supplements affect free testosterone
Grade Level of Evidence
Robust research conducted with repeated double-blind clinical trials
Multiple studies where at least two are double-blind and placebo controlled
Single double-blind study or multiple cohort studies
Uncontrolled or observational studies only
Level of Evidence
? The amount of high quality evidence. The more evidence, the more we can trust the results.
Outcome Magnitude of effect
? The direction and size of the supplement's impact on each outcome. Some supplements can have an increasing effect, others have a decreasing effect, and others have no effect.
Consistency of research results
? Scientific research does not always agree. HIGH or VERY HIGH means that most of the scientific research agrees.
grade-c Dehydroepiandrosterone Minor Very High See 2 studies
Increases in free testosterone have been noted to coincide with testosterone increases (which are unreliable)
grade-c Zinc Minor Very High See 2 studies
Free testosterone follows the same trends as testosterone, and may be increased following supplementation in persons who are deficient in zinc
grade-c Chromium - Very High See 2 studies
No significant influence of chromium supplementation on free testosterone concentrations in women with PCOS.
grade-c Nigella sativa  
grade-c Velvet Antler  
grade-c Vitamin E  
grade-d Boron  
grade-d Calcium  
grade-d D-Aspartic Acid  
grade-d Tribulus terrestris  

All comparative evidence is now gathered in our ​A-to-Z Supplement Reference.

The evidence for each separate supplement is still freely available ​here.