Tongkat Ali and SHBG: How Freeing Bound Testosterone Works
Your total testosterone number on a blood test doesn't tell the whole story. A large portion of circulating testosterone is bound to Sex Hormone Binding Globulin (SHBG) and is biologically inactive. Tongkat Ali appears to reduce SHBG levels, effectively increasing the "free" testosterone available for your muscles, brain, and libido to use — even without increasing total testosterone production.
What is SHBG and why does it matter?
Sex Hormone Binding Globulin (SHBG) is a glycoprotein produced by your liver that binds to three hormones: testosterone, dihydrotestosterone (DHT), and estradiol (estrogen). When testosterone is bound to SHBG, it's essentially locked up — unavailable to interact with androgen receptors in your muscles, brain, bones, or reproductive tissue. Think of SHBG as a storage locker: testosterone inside the locker exists on your blood test but can't do its job.
Only about 2-3% of your total testosterone circulates as truly "free" testosterone — unbound and immediately bioavailable. Another 25-40% is loosely bound to albumin (and somewhat available). The remaining 60-70% is tightly bound to SHBG and functionally inactive.
This means two men can have identical total testosterone levels but very different functional testosterone status depending on their SHBG levels. A man with total testosterone of 600 ng/dL and low SHBG may feel sharp, strong, and energetic. A man with the same 600 ng/dL but high SHBG may feel fatigued, low-libido, and weak — because much less of his testosterone is actually available for use.
What causes high SHBG?
SHBG levels increase with aging (roughly 1-2% per year after 40), hyperthyroidism, liver disease, low calorie or very low carbohydrate diets, estrogen dominance, and certain medications (particularly anticonvulsants and some antidepressants). Lifestyle factors like chronic undereating and excessive endurance training can also elevate SHBG.
SHBG tends to decrease with obesity (paradoxically — obese men often have low SHBG but also low free testosterone due to other mechanisms), insulin resistance, hypothyroidism, and anabolic steroid use.
How Tongkat Ali affects SHBG
Tongkat Ali (Eurycoma longifolia) appears to influence testosterone availability through multiple pathways, and SHBG reduction is one of the most significant.
SHBG reduction. Multiple studies and conference presentations have reported that Tongkat Ali supplementation decreases circulating SHBG levels. By reducing the amount of SHBG available to bind testosterone, a greater proportion of total testosterone remains in its free, bioavailable form. This effect appears most pronounced in men whose SHBG is elevated to begin with — which is consistent with how the compound is generally discussed in the sports-science literature, and with the limitation noted further down: men already at the low end of the SHBG range have less room to benefit from this particular mechanism.
LH stimulation. Tongkat Ali's bioactive compound eurycomanone acts on the hypothalamic-pituitary-gonadal (HPG) axis to increase luteinizing hormone (LH) release, which signals the testes to produce more testosterone. This is a direct production pathway, distinct from the SHBG mechanism.
Weak aromatase inhibition. Tongkat Ali may inhibit aromatase (the enzyme that converts testosterone to estrogen), though this effect appears to be modest compared to pharmaceutical aromatase inhibitors. By reducing estrogen conversion, more testosterone remains intact.
Cortisol reduction. Tongkat Ali has documented effects on reducing cortisol — the stress hormone that directly suppresses the HPG axis and inhibits testosterone production. Lower cortisol creates a more favorable hormonal environment for testosterone synthesis.
What the research shows
A 2022 meta-analysis of 9 randomized controlled trials confirmed that Tongkat Ali significantly increased serum testosterone (SMD = 1.352, p = 0.001). While the meta-analysis focused on total testosterone, the individual studies within it — and additional conference-presented data by Dr. Tambi and colleagues — reported SHBG reductions as a contributing mechanism.
The effect appears dose-dependent, with most studies using 200-400mg per day of standardized extract. XWERKS Rise contains 400mg — the upper end of the research-validated range.
Who benefits most from SHBG reduction?
Men with high SHBG and normal total testosterone benefit the most. This profile is common in men over 40, men on very low-carb diets, lean men with low body fat, and men with thyroid imbalances. If your blood work shows total testosterone in the "normal" range but free testosterone is low, SHBG is likely the bottleneck.
Men with already low SHBG (common with obesity and insulin resistance) are less likely to see dramatic benefit from SHBG-targeting interventions because their SHBG isn't the limiting factor. For these men, the LH-stimulation and cortisol-reduction pathways of Tongkat Ali may be more relevant.
Important limitations
Much of the SHBG-specific data for Tongkat Ali comes from conference presentations rather than peer-reviewed publications, making it lower on the evidence hierarchy than the total testosterone data from the 2022 meta-analysis. The SHBG mechanism is biologically plausible and supported by the free testosterone improvements seen in published studies, but direct, large-scale, peer-reviewed SHBG measurement data remains limited.
Additionally, SHBG serves a protective function — it prevents testosterone from being cleared too quickly and helps regulate hormonal balance. Extremely low SHBG (as seen with insulin resistance) is not desirable. The goal is optimal SHBG, not minimal SHBG.
The Bottom Line
SHBG determines how much of your total testosterone is actually available for your body to use. Tongkat Ali appears to reduce SHBG levels, increase LH-driven testosterone production, weakly inhibit aromatase, and reduce cortisol — all of which contribute to greater bioavailable testosterone.
The effect is strongest in men with elevated SHBG (common with aging, lean body composition, and low-carb diets). At 200-400mg/day, Tongkat Ali is among the most evidence-backed natural compounds for addressing the SHBG-to-free-testosterone bottleneck — though the SHBG-specific data is weaker than the total testosterone data. Combined with Boron and Zinc, it provides multi-pathway testosterone support.
Further Reading
Tongkat Ali FAQ — Complete research review with 10 references.
Cortisol vs. Testosterone — How chronic stress suppresses the HPG axis.
Testosterone-Killing Foods — Dietary patterns that affect hormonal balance.
Testosterone Levels by Country — The lifestyle factors driving global testosterone differences.
References
1. Leisegang K, et al. Eurycoma longifolia (Jack) improves serum total testosterone in men: a systematic review and meta-analysis of clinical trials. Medicina. 2022;58(8):1047.
2. Talbott SM, et al. Effect of Tongkat Ali on stress hormones and psychological mood state in moderately stressed subjects. JISSN. 2013;10(1):28.
3. Tambi MI, Imran MK. Eurycoma longifolia Jack in managing idiopathic male infertility. Asian J Androl. 2010;12(3):376-380.
4. Hammond GL. Diverse roles for sex hormone-binding globulin in reproduction. Biol Reprod. 2011;85(3):431-441.
5. Naghii MR, et al. Comparative effects of daily and weekly boron supplementation on plasma steroid hormones and proinflammatory cytokines. J Trace Elem Med Biol. 2011;25(1):54-58.
