A glycoprotein produced mainly in your liver, SHBG binds with testosterone and oestradiol in your blood, transporting them to other tissues in your body.

High levels of SHBG are often found in men with hyperthyroidism (an overactive thyroid) and cirrhosis of the liver. High levels of SHBG can also reduce the amount of free testosterone available in your body, leading to a decreased sex drive, reduced muscle mass, erectile dysfunction and low sperm production. Low levels of SHBG mean your body has more free testosterone available. This can cause mood swings, an increased muscle mass and weight gain.