SHBG: What It Is, Why It Matters, and How to Fix It

Your testosterone came back at 650 ng/dL. Your doctor said everything looks fine. But you're still exhausted, your libido is gone, and you haven't been able to gain muscle in two years.

Here's what nobody told you: total testosterone is only half the story. The other half is SHBG (sex hormone binding globulin). And if your SHBG is elevated, a significant chunk of that 650 is locked away and useless to your cells. You don't feel it because your body can't access it.

This is the most common misread lab in hormone medicine. Most primary care doctors glance at total testosterone, say "normal," and move on. The question that actually matters is how much free testosterone you’re working with. Most doctors never answer it.

SHBG is the protein that determines that answer.

What Is SHBG (Sex Hormone Binding Globulin)?

Sex hormone binding globulin is a glycoprotein produced by the liver that binds testosterone, estradiol, and other sex steroids in the bloodstream, regulating how much of each hormone is biologically available to your tissues.

Think of SHBG as a carrier protein with a very strong grip. When testosterone is bound to SHBG, it can't enter cells, can't activate androgen receptors, and can't do any of the things testosterone is supposed to do. It's testosterone on a leash — present in your blood, but functionally unavailable.

As Hammond (2016) describes in a landmark review, SHBG acts as the "primary gatekeeper of steroid hormone action," with plasma SHBG levels directly determining the bioavailable fraction of circulating androgens and estrogens (Hammond, 2016).

About 30–45% of circulating testosterone binds tightly to SHBG. Another 50–68% binds loosely to albumin (that fraction is still considered bioavailable because the bond is weak enough to release). Only 1-3% circulates completely free: unbound, fully active, directly accessible to tissues.

So when your total testosterone reads 650 ng/dL, and 45% of it is locked to SHBG, you might have effective free testosterone levels well below what most men need to feel good. That's not a lab quirk. That's how your body actually works.

Why Free Testosterone Is What Actually Matters

Total testosterone measures everything, bound and unbound. Free testosterone measures only what your cells can access. The gap between those two numbers is determined almost entirely by your SHBG level.

Dr. Peter Attia made this exact point in a 2024 episode with Dr. Andrew Huberman: "We don't spend a lot of time looking at total [testosterone]... the way I used to spend more time looking at total and free... if a guy's got 2% of [800 ng/dL] as free or unbound, that would translate to 16 nanograms per deciliter of free testosterone." His point: free is what matters clinically, and most labs are estimating it, not measuring it directly.

The standard method for calculating free testosterone is the Vermeulen formula, which uses your total testosterone, SHBG level, and albumin to estimate the free fraction. It's not perfect — it introduces some measurement error — but it's the best widely available tool for interpreting what your total testosterone number actually means in practice.

This is why SHBG belongs on your hormone panel. Without it, you're missing a critical piece of the picture.

Araujo et al. (2007) studied 1,475 men aged 30–79 from the Boston Area Community Health Survey and found that about 24% had total testosterone below 300 ng/dL, but only 11% had free testosterone below 5 ng/dL. That gap means SHBG variation explained a substantial difference in who was actually symptomatic (Araujo et al., 2007). In other words: total testosterone alone misclassified a lot of men as deficient or sufficient. Free testosterone, which accounts for SHBG, told a more accurate story about who was actually experiencing symptoms.

What Causes Low SHBG?

Low SHBG sounds like a good thing at first. Less binding means more free testosterone, right? Sometimes. But low SHBG is almost always a downstream signal of a metabolic problem, not a trait to be optimized for.

The most common driver is insulin resistance and obesity. When insulin levels are chronically elevated, the liver produces less SHBG. Pugeat et al. (1991) showed a strong negative correlation between fasting insulin levels and SHBG in both obese and hyperandrogenic populations, with high insulin effectively suppressing SHBG production at the hepatic level (Pugeat et al., 1991). Li et al. (2010) found that men in the lowest quartile of SHBG were more than twice as likely to have metabolic syndrome compared to men in the highest quartile, in a sample of 1,226 men from the Third National Health and Nutrition Examination Survey (Li et al., 2010).

What suppresses SHBG:

• Insulin resistance and type 2 diabetes: the most consistent driver; elevated insulin directly signals the liver to produce less SHBG
• Obesity, particularly visceral fat: closely tied to insulin resistance and low-grade inflammation
• Non-alcoholic fatty liver disease (NAFLD): Simó et al. (2015) found that liver fat content, independent of BMI, is a strong determinant of circulating SHBG levels, with proinflammatory cytokines released by fatty liver tissue downregulating SHBG production (Simo et al., 2015)
• Hypothyroidism: low thyroid hormone suppresses SHBG production; normalizing thyroid function typically raises SHBG
• Anabolic steroid use: exogenous testosterone and other androgens consistently drive SHBG down; this is one of the mechanisms by which supraphysiologic androgen use increases free testosterone out of proportion to what total testosterone would suggest
• High-protein, very low-carb diets: there's emerging evidence that ketogenic and carnivore diets can suppress SHBG in some individuals; this is part of what Derek (More Plates More Dates) has flagged in the keto and carnivore communities, where sky-high SHBG in some followers is being underacknowledged

For women, low SHBG is closely associated with PCOS. Zhu et al. (2019) reviewed the relationship between SHBG and polycystic ovary syndrome, finding that low serum SHBG is both a consequence and a diagnostic marker of insulin resistance and hyperandrogenism in PCOS, with SHBG gene polymorphisms also playing a role in susceptibility (Zhu et al., 2019).

What Causes High SHBG?

High SHBG is the opposite problem. It binds up too much testosterone, leaving the free fraction too low to support normal function. This is where men with "normal" total testosterone can feel genuinely hypogonadal.

Aging is the most universal driver. SHBG increases steadily with age in men, which is part of why free testosterone drops significantly faster than total testosterone over the decades. Diver et al. (2003) confirmed significant diurnal rhythms in both total and free testosterone in middle-aged men, with SHBG levels showing their own circadian pattern, which is relevant for timing your labs correctly (Diver et al., 2003).

What raises SHBG:

• Aging: SHBG climbs reliably after 40, accelerating the drop in free testosterone even when total stays stable
• Hyperthyroidism: elevated thyroid hormone is one of the strongest drivers of high SHBG; an overactive thyroid can push SHBG dramatically above range
• Liver disease: while fatty liver lowers SHBG, inflammatory liver disease and cirrhosis can paradoxically raise it in some cases
• Very low calorie intake: prolonged caloric restriction or crash dieting raises SHBG, partly explaining why aggressive diets leave people feeling lousy despite weight loss
• Oral estrogen therapy: oral estrogens taken by postmenopausal women or trans women who use oral estradiol substantially increase SHBG because the liver first-pass effect amplifies the estrogenic signal; transdermal estrogen does not have this effect to the same degree
• Certain medications: anticonvulsants (particularly phenytoin and carbamazepine), some antifungals, and thyroid medication if overdosed can all raise SHBG

Rannevik et al. (1995) followed 160 women through menopause over 12 years and documented SHBG changes alongside steroid hormones and bone density, confirming that SHBG shifts are tightly coupled to the estrogen-testosterone balance during hormonal transitions (Rannevik et al., 1995).

High SHBG also carries clinical consequences beyond just low free testosterone. Mellström et al. (2008) studied 2,639 older men and found that high SHBG was directly and independently associated with fracture risk, with each standard deviation increase in SHBG associated with a 41% higher risk of fracture (HR 1.41, 95% CI 1.22–1.63) , an effect that persisted after adjusting for bone mineral density, suggesting SHBG may affect bone independently of the sex steroids it carries (Mellstrom et al., 2008).

How to Read Your SHBG Lab Results

Standard reference ranges vary by lab, but general adult guidelines look like this:

Men:

• Low: below 10–13 nmol/L (associated with insulin resistance, metabolic syndrome)
• Normal: 10–57 nmol/L (most functional ranges favor the 20–40 nmol/L zone)
• High: above 57 nmol/L (associated with low free testosterone symptoms)

Women (premenopausal):

• Low: below 25–30 nmol/L (associated with PCOS, insulin resistance)
• Normal: 25–122 nmol/L
• High: above 122 nmol/L (less common; associated with thyroid overactivity, liver disease)

These are reference ranges. They tell you where you fall relative to a population average, not where you need to be to feel optimal. Many men feel their best with SHBG in the 20–35 nmol/L range. Some need slightly higher or lower. What matters most is how your free testosterone looks once your SHBG number is in the picture.

When to get tested: Ideally in the morning (7–10 AM), fasted or in a consistent fed state. SHBG has a diurnal rhythm, rising through the day in parallel with cortisol. Morning labs give the most consistent results and the most accurate free testosterone calculation.

What to test alongside SHBG: Total testosterone, free testosterone (calculated or direct), albumin, LH, FSH, estradiol, thyroid panel (TSH, free T3, free T4), fasting insulin, and a full metabolic panel. SHBG doesn't tell you much in isolation. It's one piece of a larger picture.

SHBG's Role in TRT Dosing

This is where SHBG gets clinically important for anyone on testosterone replacement therapy.

Your SHBG level significantly affects how your body responds to a given TRT dose and how often you need to inject. Low SHBG and high SHBG patients need very different dosing approaches.

Low SHBG on TRT: Men with low SHBG tend to have a larger peak-to-trough swing in free testosterone between doses. Their free testosterone spikes high after an injection and drops faster. This often translates to emotional instability, energy crashes in the days before the next dose, and a tendency for estradiol to peak disproportionately high early in the dosing cycle. For these patients, more frequent dosing (twice weekly or even every other day with smaller amounts) smooths the curve and improves subjective response.

High SHBG on TRT: Men with high SHBG often need a higher total weekly dose to achieve the same free testosterone levels. Their SHBG is mopping up so much of what they're putting in that standard doses leave them underdosed. Some clinicians also extend their dosing intervals to weekly instead of twice-weekly, because SHBG itself helps buffer the drop, maintaining steadier free testosterone levels over the week.

Peter Attia's perspective in his TRT episode is worth noting: "the more frequently you can take [testosterone] the better... twice a week is really nice... if you go to a testosterone clinic giving you 200 [mg] every two weeks, 50 twice a week is the same total dose." But for high-SHBG patients, some providers actually find weekly dosing works better because the protein buffering maintains free levels more consistently.

The bottom line: a HEXIS protocol doesn't guess at dosing. Your SHBG level is one of the first things your provider uses to determine starting dose, delivery method, and frequency. Getting that number wrong means your protocol will be off from day one.

What Affects SHBG Levels You Can Actually Change

SHBG is not fixed. Several lifestyle and clinical factors move it meaningfully.

Weight loss and metabolic improvement is the most reliably effective intervention. If insulin resistance is driving your low SHBG, losing visceral fat and improving insulin sensitivity will raise it. Peter et al. (2010) showed that in a 9-month lifestyle intervention study, SHBG levels correlated positively with insulin sensitivity measured by glucose clamp, and the relationship was largely mediated by liver fat. Less liver fat, higher SHBG (Peter et al., 2010).

Thyroid correction: if your thyroid is the problem, treating it is the intervention. Low SHBG from hypothyroidism responds well to thyroid hormone replacement. High SHBG from hyperthyroidism normalizes when thyroid levels come under control.

Reducing alcohol: chronic alcohol use, even at moderate levels, can alter liver function in ways that affect SHBG production. Reducing alcohol intake often shows improvement within weeks.

Insulin-sensitizing strategies: improving metabolic health through diet, exercise, sleep, and weight management is the most sustainable approach. Time-restricted eating has also shown some promise: Li et al. (2021) ran a 6-week time-restricted feeding trial in 15 women with anovulatory PCOS and found improvements in SHBG, HOMA-IR, LH/FSH ratios, and menstrual cycle regularity, without significant caloric restriction (Li et al., 2021).

Addressing medications: if an anticonvulsant or another medication is driving high SHBG, that's a conversation with the prescribing physician. Switching delivery methods (e.g., from oral to transdermal estrogen) can also reduce SHBG in women who are on hormone therapy.

Boron comes up constantly on Reddit. Some evidence suggests supplemental boron (3-10 mg/day) may modestly lower SHBG in some individuals, but the data is thin and the effect size small. Not a primary intervention. Address the metabolic root cause first.

SHBG in Women: A Different Picture

Everything above applies to women too, but with some important differences.

In women, SHBG regulates the bioavailability of estradiol and testosterone. Since women have much lower baseline testosterone levels, a change in SHBG has a proportionally larger effect on how much testosterone is available. A woman with SHBG of 90 nmol/L and total testosterone of 30 ng/dL may have essentially no functional free testosterone, contributing to symptoms like low libido, poor muscle tone, brain fog, and fatigue. These are symptoms that are often attributed to estrogen or menopause but are actually driven by the SHBG-testosterone dynamic.

For perimenopausal and postmenopausal women, SHBG levels typically rise as estrogen falls, further squeezing the already-low free testosterone fraction. This is why women starting testosterone therapy for menopause symptoms sometimes see limited response: their SHBG is capturing most of it before it reaches tissues.

For PCOS patients, the pattern flips. Low SHBG due to insulin resistance allows more free testosterone to circulate, contributing to androgenic symptoms (acne, hirsutism, irregular cycles). Jayagopal et al. (2003) found SHBG to be a more stable and consistent marker of insulin resistance in PCOS than either HOMA-IR or testosterone alone, with PCOS patients showing SHBG of 28.6 vs. 57.6 nmol/L in controls (p=0.001), suggesting SHBG may be useful as a surrogate marker for metabolic health in this population (Jayagopal et al., 2003).

When to Recheck

If you're making lifestyle changes to address abnormal SHBG, give the intervention time before rechecking:

• After starting or adjusting thyroid medication: retest in 6–8 weeks, alongside thyroid levels
• After significant weight loss (10+ lbs): retest in 3 months
• After improving metabolic health / reducing insulin resistance: retest in 3–6 months
• After changing TRT protocol: retest in 6–8 weeks, alongside full hormone panel
• After starting or stopping oral estrogen: retest in 6–8 weeks

SHBG doesn't move overnight. The liver needs time to adjust production rates in response to changing hormonal and metabolic signals. If you retest too early, you'll see incomplete data and potentially make premature protocol changes.

Routine monitoring: for anyone on TRT or HRT, SHBG should be part of every routine lab panel, typically every 3–6 months once a protocol is stable, and 6–8 weeks after any dose or delivery method change.

Cost, Coverage, and Access

What an SHBG test costs: As a standalone add-on to a standard hormone panel, SHBG testing typically runs $20–60 at major lab networks (LabCorp, Quest) when ordered by a physician. Many commercial insurers will cover it when ordered for clinically documented symptoms of hormone imbalance, though prior authorization policies vary.

Ordering on your own: Direct-to-consumer lab platforms (Ulta Lab Tests, Marek Health, Let's Get Checked, and others) allow you to order SHBG without a physician visit, typically for $30–80 as part of a hormone panel bundle.

Through HEXIS: SHBG is included in the standard HEXIS hormone panel, which your provider reviews as part of your first consultation. There's no guesswork about what to order. Your HEXIS provider will look at total testosterone, free testosterone, SHBG, estradiol, LH, FSH, thyroid, and metabolic markers together, so the interpretation is always in context.

If your SHBG is abnormal, your HEXIS provider will work with you to identify the likely cause, adjust your protocol if you're on TRT or HRT, and build a monitoring plan appropriate to your situation. HEXIS sees patients both in person in Great Falls, MT and via telehealth across Montana, Washington, Idaho, and Oregon.

FAQ

What is a normal SHBG level for men?

Most labs report normal SHBG for adult men as 10–57 nmol/L, though functional medicine practitioners often target 20–40 nmol/L for optimal hormone bioavailability. Values below 10 nmol/L strongly suggest insulin resistance or metabolic syndrome. Values above 57 nmol/L, especially paired with low-normal total testosterone, can produce clinical symptoms of low testosterone even when total testosterone appears adequate.

Can high SHBG make you feel low testosterone symptoms even with normal total testosterone?

Yes, and this is one of the most underrecognized problems in hormone medicine. If your SHBG is elevated, a larger fraction of your total testosterone is biologically inactive. A man with total testosterone of 600 ng/dL and SHBG of 75 nmol/L may have free testosterone levels equivalent to someone with total testosterone of 350 ng/dL and normal SHBG, and experience the same symptoms of fatigue, low libido, and poor body composition as a result.

Does losing weight lower SHBG or raise it?

It depends on what's abnormal. If you have low SHBG driven by insulin resistance, losing visceral fat and improving insulin sensitivity will raise it toward normal. If you have high SHBG, modest weight loss doesn't consistently lower it. You'd need to address the specific driver (thyroid, medication, etc.). Extreme caloric restriction or crash dieting can paradoxically raise SHBG in anyone, including those already high.

How does anabolic steroid use affect SHBG?

Exogenous androgens, including testosterone used at supraphysiologic doses, consistently and significantly suppress SHBG. This is partly why anabolic steroid users can have very high free testosterone fractions even at moderate total testosterone levels — the SHBG that would normally bind the majority of circulating testosterone is suppressed. When androgens are stopped, SHBG rebounds, often sharply, causing a temporary period of low free testosterone during recovery.

Should I test SHBG if I feel fine on TRT?

Yes, periodically. Even if you feel good, SHBG monitoring helps your provider understand whether your free testosterone is where it should be and whether your dose is still appropriate as your body composition, age, and metabolic health change. SHBG tends to rise with age, meaning a dose that was appropriate at 40 may not be adequate at 50 with the same total testosterone target. Routine monitoring avoids underdosing or overdosing as your biology changes over time.

Working With SHBG at HEXIS

If you've had labs that showed "normal" testosterone but you're still symptomatic (fatigue, poor recovery, low libido, brain fog), SHBG is worth looking at closely. Your HEXIS provider won't just check the box and move on.

Your SHBG level tells us what your hormone picture actually looks like, not just what the headline number says. It guides dosing decisions, delivery method selection, and monitoring intervals. Whether your SHBG is too high or too low, the approach starts with understanding why, and then building a protocol around your specific physiology.

Your protocol starts with labs, not guesswork. Schedule a consultation and let's look at the full picture.

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