What Is SHBG and How Does It Affect Your Testosterone?
By TRT NYC Editorial Team
SHBG (sex hormone-binding globulin) is a protein made mainly by the liver that binds to testosterone in your blood. Testosterone bound to SHBG is inactive, so high SHBG lowers your free (usable) testosterone, while low SHBG raises it. That’s why SHBG is key to correctly interpreting your testosterone levels. Here’s how it works.
If your total testosterone is “normal” but you feel low, SHBG is one of the first things to check. It’s the hidden variable that decides how much of your testosterone is actually available to your body. (To see how that plays out, read free vs total testosterone.)
What Is SHBG?
SHBG (sex hormone-binding globulin) is a protein produced mostly by your liver. Its job is to bind and transport sex hormones primarily testosterone and estrogen, through your bloodstream. Hormone that’s bound to SHBG is held tightly and can’t be used by your cells. So SHBG acts like a sponge: the more SHBG you have, the more testosterone it soaks up and locks away.
How SHBG Affects Testosterone
SHBG directly controls your free testosterone, the small, active portion your body actually uses:
- High SHBG binds up more testosterone → less free testosterone → you can feel symptoms even with a normal total.
- Low SHBG binds less → more free testosterone available.
This is why two men with the same total testosterone can feel completely different, their SHBG (and therefore free testosterone) differs.
High SHBG vs Low SHBG
| High SHBG | Low SHBG | |
|---|---|---|
| Effect on free T | Lowers free testosterone | Raises free testosterone |
| Common causes | Aging, hyperthyroidism, liver disease, very low-calorie diets | Obesity, insulin resistance, hypothyroidism, high insulin |
| Typical impact | Low-T symptoms despite normal total | More usable testosterone (but linked to metabolic issues) |
What Causes High or Low SHBG?
SHBG goes up with: aging, an overactive thyroid, liver disease, estrogen, and prolonged calorie restriction. SHBG goes down with: obesity, insulin resistance and high insulin, an underactive thyroid, and certain medications.
Because so much of this ties to metabolic health, SHBG is also a useful window into what’s going on beyond just testosterone.
SHBG and Free Testosterone
The practical takeaway:you can’t interpret testosterone without SHBG. A normal total with high SHBG often means low free testosterone and symptoms. That’s why labs calculate free testosterone using total testosterone, SHBG, and albumin. If your free T is low because SHBG is high, the fix targets SHBG, see how to lower SHBG and increase free testosterone.
Normal SHBG Levels
Normal SHBG ranges vary by lab, age, and method, so there’s no single universal number, compare your result to your lab’s reference range. What matters most is how your SHBG affects your free testosterone and whether you have symptoms, not the SHBG number in isolation. Always interpret it alongside total and free testosterone (normal testosterone levels).
How to Lower High SHBG
If high SHBG is dragging down your free testosterone, the approach focuses on the causes. Losing excess weight, improving insulin sensitivity, treating thyroid issues, and not over-restricting calories. These can lower SHBG and free up more usable testosterone. Get the full playbook in how to lower SHBG and increase free testosterone.
The Bottom Line
SHBG is the liver protein that binds your testosterone and controls how much is free and usable. High SHBG lowers free testosterone (and can cause symptoms despite a normal total), while low SHBG raises it but often signals metabolic issues. Always test SHBG alongside total and free testosterone, it’s the missing piece that makes your labs make sense.
👉 Want to see your full picture? Use an at-home testosterone test kit and learn which panel to order so SHBG is included.
Frequently Asked Questions
What is SHBG?
SHBG (sex hormone-binding globulin) is a protein made mainly by the liver that binds and transports testosterone and estrogen in the blood. Testosterone bound to SHBG is inactive, so SHBG controls how much free, usable testosterone you have.
How does SHBG affect testosterone?
SHBG binds testosterone and makes it inactive, so high SHBG lowers your free (usable) testosterone while low SHBG raises it. This is why a normal total testosterone can still leave you symptomatic if SHBG is high.
What does high SHBG mean?
High SHBG means more of your testosterone is bound and inactive, leaving less free testosterone, which can cause low-T symptoms even with a normal total. Common causes include aging, hyperthyroidism, liver disease, and very low-calorie diets.
What does low SHBG mean?
Low SHBG means less testosterone is bound, so more is free and usable. However, low SHBG is often linked to obesity, insulin resistance, and metabolic issues, so it can be a sign to check your metabolic health.
What is a normal SHBG level?
Normal SHBG ranges vary by lab, age, and method, so there’s no single universal number, use your lab’s reference range. What matters most is how SHBG affects your free testosterone and whether you have symptoms.
How do you lower SHBG?
High SHBG can be lowered by losing excess weight, improving insulin sensitivity, treating thyroid problems, and avoiding extreme calorie restriction. Lowering SHBG frees up more usable testosterone. See our dedicated guide for the full approach.
Written by the TRT NYC Editorial Team. Reviewed against current testing guidance (Endocrine Society; MedlinePlus). Last updated: June 2026.
Medical disclaimer: This article is for educational purposes only and is not medical advice, diagnosis, or treatment. Reference ranges vary by laboratory. trtnyc.com is an independent informational resource, not a medical provider. Always interpret lab results with a licensed healthcare provider.