You can't talk seriously about testosterone support without talking about SHBG — a protein most men have never heard of but that plays a bigger role than most people realize.
Sex hormone-binding globulin (SHBG) binds to testosterone in your bloodstream. Testosterone that's bound to SHBG isn't available for your body to use — only the unbound, “free” testosterone is biologically active.
SHBG levels tend to rise with age, meaning more of your testosterone gets bound up and less is available — even if your total testosterone number looks normal on paper.
Nettle Leaf and Boron are both studied for their role in helping regulate SHBG binding, which is part of why HorseWood includes them alongside Tongkat Ali in its formula.