After spending the past several weeks dismantling the evidence behind tribulus, D-aspartic acid, and fenugreek, I want to talk about two compounds that deserve a different kind of conversation. Because not everything in the testosterone supplement space is junk science. Some ingredients have real data behind them. And intellectual honesty requires acknowledging that when the evidence is there, even if the conclusion comes with significant caveats.
Tongkat ali and ashwagandha are the two popular supplements that come closest to passing my evidence framework. They have controlled human trials. They have plausible mechanisms. They have measurable — if modest — effects on testosterone in certain populations. I'd take either of them over tribulus or DAA without hesitation.
But "closest to passing" is not the same as "passing." And understanding exactly where these two compounds fall short is, I think, more instructive than another simple debunking. The limitations here reveal something important about why most approaches to natural testosterone support hit a ceiling — and what it would take to move past it.
Tongkat Ali: The Stress-Reduction Route
Eurycoma longifolia — commonly known as tongkat ali or longjack — is a flowering plant native to Southeast Asia, particularly Malaysia, Indonesia, and Vietnam. It has been used in traditional Malay medicine for centuries as an energy tonic, aphrodisiac, and antimalarial remedy. The root contains quassinoids, particularly eurycomanone, which appear to be the primary bioactive compounds.
The tongkat ali research base is better than most in the testosterone supplement space, though that's admittedly a low bar. Two studies stand out.
Talbott et al., 2013. Published in the Journal of the International Society of Sports Nutrition, this study examined 63 moderately stressed adults (both men and women) taking 200mg of a tongkat ali extract daily for four weeks. The key findings: cortisol decreased by 16%, and testosterone increased by 37% compared to placebo. These are meaningful numbers. But the critical detail is in the study population — these were moderately stressed individuals. Their cortisol was elevated at baseline. The testosterone increase was measured in the context of cortisol reduction in people who were hormonally suppressed by stress to begin with.
Henkel et al., 2014. Published in Andrologia, this study focused on late-onset hypogonadal men — men over 40 with clinically low testosterone. After one month of tongkat ali supplementation, the researchers reported significant improvements in testosterone levels and aging male symptom scores. Again, real effects. But again, in a population that was starting from a deficit.
What the Tongkat Ali Data Actually Tells Us
The tongkat ali evidence, when you read it carefully, reveals a specific and limited mechanism of action. Tongkat ali appears to work primarily through cortisol reduction. Cortisol and testosterone exist in an inverse relationship — when chronic stress keeps cortisol elevated, it suppresses the HPG axis and directly inhibits testosterone production. By reducing cortisol, tongkat ali removes a brake on testosterone production. The result looks like a testosterone increase, but the mechanism is stress mitigation, not production enhancement.
This is a meaningful distinction. If your testosterone is low because you're chronically stressed, tongkat ali may genuinely help. It's addressing a real bottleneck. But if your cortisol is already well-managed — if stress isn't the primary factor suppressing your T — the compound has much less to offer. You can't reduce cortisol below healthy levels, and even if you could, it wouldn't push testosterone higher.
The data in healthy, non-stressed men is considerably less impressive than the headline numbers from stressed populations would suggest. This is a supplement that helps most when you need it least to be a "testosterone booster" — because if stress is your primary issue, the solution is stress management, not supplementation. Tongkat ali just happens to assist with one aspect of that.
Ashwagandha: The Strongest Case in the Adaptogen Category
Withania somnifera — ashwagandha — is the supplement I give the most credit to in this entire review series. Not because it's perfect. Not because it's the final answer. But because the evidence behind it is genuinely solid by supplement industry standards, and I have to call that what it is.
Ashwagandha is a plant in the Solanaceae (nightshade) family, used extensively in Ayurvedic medicine as a Rasayana — a rejuvenation tonic. The primary bioactive compounds are withanolides, steroidal lactones concentrated mainly in the root. The most well-studied extract is KSM-66, a full-spectrum root extract standardized to 5% withanolides.
The Evidence
Lopresti et al., 2019. Published in The Aging Male, this randomized, double-blind, placebo-controlled trial enrolled 57 overweight men aged 40-70 with mild fatigue. Participants received 300mg of ashwagandha root extract (KSM-66) twice daily for 8 weeks. The results: a 14.7% increase in testosterone compared to placebo, along with an 18% increase in DHEA-S. Cortisol decreased by 11.4% in the ashwagandha group. These are well-measured, statistically significant, clinically relevant effect sizes in a properly designed trial.
Wankhede et al., 2015. Published in the Journal of the International Society of Sports Nutrition, this study examined 57 young resistance-trained men taking 300mg of ashwagandha extract twice daily for 8 weeks during a strength training program. The ashwagandha group showed significantly greater increases in muscle strength and size compared to placebo, and testosterone levels increased significantly more in the ashwagandha group. This is one of the few supplement studies that demonstrates both hormonal and functional outcomes in an active, healthy population.
These are not garbage studies. They're well-designed, adequately powered, properly controlled, and published in legitimate journals. The effects are real. I want to be clear about that: ashwagandha has genuine evidence supporting a modest testosterone-enhancing effect. If someone asked me to rank popular testosterone supplements by evidence quality, ashwagandha would be near the top.
But Here's the Limitation
When you examine the mechanism carefully, ashwagandha's testosterone effect follows the same fundamental pathway as tongkat ali: cortisol reduction leading to reduced HPG axis suppression. Ashwagandha is classified as an adaptogen — a compound that helps the body manage physiological stress responses. Its primary measurable hormonal effect is a reduction in cortisol. The testosterone increase appears to be a downstream consequence of that cortisol reduction, not a direct enhancement of testosterone synthesis.
The practical implication is significant: there's a ceiling. Once cortisol is adequately managed — once the stress-related suppression of the HPG axis is resolved — ashwagandha has diminishing returns for testosterone. You can remove a brake, but removing a brake is not the same as pressing the accelerator.
The effect sizes, while real, are modest in absolute terms. The Lopresti study showed an increase of approximately 50-80 ng/dL in total testosterone. For a man starting at 350 ng/dL, that could bring him to 400-430 ng/dL — a noticeable improvement, but still in the low-normal range. And the strongest results consistently appear in populations where stress or excess weight are suppressing testosterone to begin with. In healthy, lean, low-stress men, the effect sizes shrink considerably.
Cortisol Reduction vs. Production Enhancement
This is the conceptual distinction that ties this entire review series together. When I evaluate testosterone-support compounds, I'm asking a fundamental question: does this compound help the body produce more testosterone, or does it simply remove a factor that's suppressing production?
Both are valuable. If your testosterone is low because chronic stress has your cortisol through the roof, a compound that lowers cortisol will measurably help. Tongkat ali and ashwagandha do this. The evidence is real.
But for most men — particularly men over 35 who are experiencing the gradual age-related decline in testosterone that affects the majority of the male population — cortisol isn't the primary bottleneck. The primary bottleneck is the production chain itself: precursor availability, enzymatic activity at each conversion step, Leydig cell health and mitochondrial function, and the efficiency of the HPG axis signaling cascade.
Addressing cortisol is addressing one input to a multi-input system. It's a valid piece of the puzzle. But it's one piece, and for men whose stress levels are already reasonable, it's not the piece that's missing.
My Honest Assessment
Tongkat ali and ashwagandha are the closest thing to legitimate testosterone support in the popular supplement space. They have real mechanisms, real data, and real effects. If you're highly stressed, either one may help. I'd take either over tribulus, D-aspartic acid, or fenugreek without a moment's hesitation.
But neither addresses the core production chain — the HPG axis. They work on one input (cortisol) rather than the production machinery itself. That's why the effect sizes plateau. That's why the most impressive results show up in stressed and overweight populations, where cortisol suppression is a significant factor. And that's why, for the average man looking for meaningful, sustained testosterone support, these compounds are helpful but incomplete.
For most men, the real bottleneck isn't cortisol — it's the production chain itself: precursor availability, enzyme activity, Leydig cell health. The question I kept coming back to in my research was whether any natural compound exists that addresses these production-chain factors directly, rather than working on the periphery through stress modulation.
It took me a long time to find a compound that fit that description. When I did, the mechanism of action was fundamentally different from anything I'd seen in the adaptogen category — it supported mitochondrial function in Leydig cells, enhanced precursor pathways, and produced testosterone increases while maintaining LH and FSH levels (indicating the HPG axis was working with the compound, not being suppressed by it). I wrote a detailed analysis of that data in my Shilajit clinical review.
For the framework behind all of these evaluations, see Why Most Supplement Studies Are Worthless. For a detailed explanation of the HPG axis and why it matters for testosterone production, see my HPG axis deep dive.