January 3, 2023

Does Tongkat Ali (Longjack) Really Increase Testosterone? | Scientific Studies

by Bryan Wellington

Few herbal supplements have generated as much buzz in the “male enhancement” world like Tongkat Ali. Also known as Longjack, and its scientific name, Eurycoma longifolia. With all the interest and click-bait surrounding this herb, I knew I had to take a hard look at the science behind the herb.

In this article I’ll look at the evidence behind the buzz, and I’ll also look at whether Tongkat Ali is safe.

Key Findings

There is substantial evidence that Tongkat Ali is associated with increased testosterone in humans.

Unlike other supplements, these results appear to be consistent among younger, active adults, aging males, and people in between.

✲ The exact mechanism of Longjack (Tongkat Ali) isn’t known, though it’s theorized it results in “freeing” testosterone from plasma cells.

The US FDA has no official statement on Tongkat, but a European agency has listed it as potentially toxic.

Primary Findings

Our primary data come from a couple of studies that are around a decade old. This does nothing to diminish the validity of their results. In fact, as we’ll see, they actually have been supported by all of the later findings.

The first study was actually published in a journal known as an authority on hormones, Andrologia, and was actually the first-of-its kind study of Tongkat Ali in humans. Scientists in this trial wanted to address the serious condition of hypogonadism, the clinical name for low testosterone. Researchers found that one month of 200 mg/day Tongkat Ali improved testosterone in over 55% of the men.

The next study, published in the journal Phytotherapy Research, looked to determine if Tongkat Ali could help with the symptoms of aging in males and females. They found significant increases in testosterone and strength in both test groups. Two notes for what we’ll discuss later, the dose was 400 mg/day, and the proposed mechanism was the un-binding of testosterone from blood cells.

The only study I could find that had “no” evidence of testosterone increases actually wasn’t testing blood testosterone, but urinary testosterone. It was actually a study comparing different anti-doping methods, and did not make any definitive claims about total testosterone. I point this out because some sources I’ve seen quote this study as a refutation of Longkat, when this study doesn’t do that at all–it’s a comparison of blood, urine, and saliva tests to determine their strengths and weaknesses.

In Healthy Individuals

Sometimes it can take quite a lot of digging through old, scanned documents to find studies that flew under the radar when they came out. Case in point, a highly focused study of male bicyclists consumed 100 mg of Tongkat Ali just before exercise, and their testosterone and cortisol levels were measured afterward. The study found that cortisol levels were over 32% lower, and testosterone was over 16% higher.

For those who haven’t read through every article I’ve ever written, cortisol and testosterone have an inverse relationship–when cortisol goes up, testosterone goes down. Which is why anti-stress herbs like Ashwagandha are possibly effective for testosterone and weight loss.

Best Studies to Date

Anyone who is well-read on scientific literature may have noticed a key phrase missing from the studies I’ve quoted so far: placebo controlled. Well, kudos to you, and also to the authors of the next two studies, one of whom even authored the study on bicyclists.

From Bikes to Stress

Publishing in the Journal of the International Society of Sports Nutrition, the bicyclists’ researchers wanted to build on the correlation they found between cortisol, Tongkat Ali, and testosterone. They found volunteers for a placebo controlled study of psychologically stressed individuals (men and women), and had the test group take 200 mg/day for four weeks.

In the study they found a statistically significant improvement in tension, anger, and confusion–and a statistically significant drop in cortisol (-16%) and increase in testosterone (+37%).

Most Rigorous Study

The best-run study I’ve found is also the most recent. Published in the journal Maturitas, researchers conducted a six-month long, double-blind, placebo-controlled study with 45 men. Primary outcomes were erectile dysfunction and testosterone levels.

While their publicly available data doesn’t show their raw numbers, I was able to contact a University friend who has access to paid library memberships and he was able to get me the goods: using Longkat Ali increased testosterone by 55% in test men. All of the data passed the standard of statistical significance (p = 0.05 for those who are interested), while some data for testosterone increases in the test groups came in at staggering p = 0.003.

Mechanisms and Safety

It’s important in medicine to know if something works, but sometimes it’s just as important to know how something works. Sticking with testosterone, researchers learned early on that artificial steroids increase strength. But only after learning how they worked did they learn how dangerous steroids really were. Learning the mechanisms also led to lowering the doses of steroids so they could safely and effectively treat everything from acne to bronchitis.


In the article I mentioned earlier, studying the effects of Longkat Ali on stress, the authors made a few key observations. One, of course, is that there may be a link between the lowering of cortisol and the subsequent increase in testosterone. The other link they made was that, like the study of aging men and women, the mechanism may be in the separating of testosterone from blood cells.

In the body, male and female, up to 98% of testosterone is bound to either sex-hormone binding globules (SHBG) or albumin (both types of blood cells). Testosterone bound to albumin is still considered “bioavailable” because the body can still use it. It has become a hot-button concept in testosterone research to determine if a given compound can split the testosterone off of the SHBG, where the body can’t use it.

At this point, more cellular research needs to be conducted to determine what, exactly, Tongkat Ali is doing–working with the hormone cortisol, or with blood cells. 


Two important factors continued to show up in my research–1) that the Tongkat Ali was a hot-water extract, and 2) that the dose was always between 100 mg and 400 mg per day.

To the first factor, the hot-water extract method is the only one that all the authors of all the studies found had the proper compounds (eurycomanone, polysaccharides, glycosaponins, and quassinoids). For further support of this method, consider that it has been jointly patented by no less a team of authorities than the Government of Malaysia and the Massachusetts Institute of Technology (MIT).

Second, there are varying reports about the safety of Tongkat Ali, based on dosage. All of the research I have quoted found no evidence of side-effect or tissue damage, allowing that all studies stayed under the 400 mg dose. The authors of one study did note that there is toxicity to animals in studies that exceeded these doses.

The safety of Longkat Ali has been corroborated by other trusted sources. However, I should note that the European Food Safety Authority has deemed that the “safety of [Tongkat Ali] has not been established under any condition of use.”

Additionally, the FDA of the Philippines has issued a warning about a consumer brand of Longkat Ali–though that was not in conjunction with safety, per se, but with authorized sales.

What then of the US? A clinical trial has been approved by the US government, but results are not yet available. The only other US warning is about a Longkat Ali supplement claiming to be a treatment for malaria–which is of course illegal to claim without FDA approval.


This has been one of my longest articles, to date, on a testosterone ingredient, and that’s largely owing to the sheer number of studies I found with unique parameters but corroborating results. In scientific research, if we see the same or similar results no matter how many different ways we can test it, that speaks to a high confidence of correlation, if not outright causation.

In this case, I also wanted to address the safety of Longkat, because there does appear to be some discrepancy in sources. It is important to address these issues when serious health concerns may be on the line.

Longkat Ali does appear to satisfy the statistical and clinical thresholds for increasing testosterone, and has done so with apparent safety. There is, however, more research to be done on the exact nature of its mechanisms, as these will help settle the differences in safety determinations and the doses that prove most effectual.


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