European research has demonstrated that a concentrated extract from Stinging Nettle (Urtica dioica) root contains a unique pathway for increasing free testosterone levels in blood.  A particular molecule in this extract has the ability to bind to sex hormone binding globulin (SHBG) thus blocking the binding of testosterone.  This allows more free testosterone to circulate in the blood.  It is free testosterone that brings about the masculinization process not bound testosterone.  Bound testosterone is not available to work on the body.  It has been demonstrated that Nettle root extract components can actually displace testosterone when it is bound to SHBG.  Nettle root extract contains divanillyltetrahydrofuran which binds to SHBG.  Divanillyltetrahydrofuran is a lignan with the highest binding affinity of lignans.  Researchers have also shown that Nettle root is beneficial to prostrate health.  It is known that a metabolite of testosterone known as dihydrotestosterone (DHT) stimulates the prostate to grow eventually leading to prostate enlargement which generates urinary issues.  Nettle root contains components that inhibit the binding of DHT to various sites found on the prostate membrane thereby preventing benign prostatic hyperplasia.  Stinging Nettle root is often used in Europe to treat enlarged prostates.  Onnit’s T-Plus contains Stinging Nettle root which may boost free testosterone levels increasing your chances of developing more muscle mass.

Active and Inactive Testosterone

Most of the testosterone (around 90 percent) is made in the testes.  The other 10 percent is made in the adrenal glands.  As a steroidal hormone, testosterone is known to increase libido by acting on the brain and also functions as an anabolic hormone in developing skeletal muscle and bone.  Testosterone becomes bound to sex hormone binding globulin (SHBG) when in the blood stream and very small amounts (around 2 percent) remains free in solution.  The rest of the testosterone is bound to albumin (around 20 percent).  Bound testosterone is not available to cell receptor sites and does not participate in skeletal muscle and bone development or libido-effects.  As males age, testosterone levels fall bringing about decreased libido, weight gain, muscle loss, and bone loss.  At this point in time, it is desirable to increase free-levels of testosterone to bring back sex drive, muscle tissue, and strong bones.

Testosterone levels can begin dropping as early as 35 years of age.  As testosterone levels begin to drop, interestingly SHBG levels begin to rise and in fact may increase by 40 percent.  So, as you age you end up with lower levels of free testosterone to maintain your masculinity.  SHBG is thought to be part of the aging process. 

It has also been reported that the liver is involved with testosterone binding to SHBG.  Moreover, this liver-induced binding is increased with various drugs and alcohol consumption.  Excessive use of antihypertension medications, transquilizers, and sedatives decrease libido.  In particular, beta-blockers and antidepressants are known to bring about sexual dysfunction. 

It would seem reasonable that if it is possible to block testosterone from binding to SHBG that libido, muscle mass, and bone density would return to normal.  Simply, having more free testosterone available should maintain masculinity.  Furthermore, Stinging Nettle root inhibits an enzyme known as 5-alpha reductase.  This enzyme is responsible for conversion of testosterone into dihydrotestosterone (DHT).  Recall that excess DHT causes prostatic hyperplasia (enlarged prostate) as well as hair loss.  Research has demonstrated that Nettle root extract contains divanillyltetrahydrofuran.  This molecule is responsible for displacing testosterone from SHBG.


Researchers have shown that concentrated Stinging Nettle root extract contains a molecule that has the ability to bind SHBG and block testosterone binding.  The molecule that is supposed to be responsible for this activity is known as divanillyltetrahydrofuran.  Blocking of testosterone binding to SHBG is believed to have the ability to boost free testosterone plasma levels.  If you are a body builder or just want to raise low testosterone levels, Stinging Nettle root extract may be able to raise free testosterone levels which promotes increased libido, muscle mass, and healthy bone mass.  Onnit’s T-Plus contains a number of ingredients important for building muscle mass and Stinging Nettle root is one of them.  T-plus boosts testosterone levels from a number of perspectives as well as blocking estrogen production to ensure high levels of testosterone.  

Resource List:

Natural Products as Aromatase Inhibitors

Interaction of lignans with human sex hormone binding globulin (SHBG).

Sex hormone binding globulin and aging.

Sex hormone-binding globulin influences gene expression of LNCaP and MCF-7 cells in response to androgen and estrogen treatment.