Tongkat Ali, Horny Goat Weed and Saw Palmetto: What the Human Evidence Actually Shows

What is Tongkat Ali, and what does the human research show?

Tongkat Ali is the root of Eurycoma longifolia, a Southeast Asian shrub used traditionally as a male tonic and now the most common botanical in testosterone-branded supplements. It is also the one ingredient in this group with a real body of randomised human data behind it.

The most useful summary is a 2022 systematic review and meta-analysis in Medicina, which screened the literature down to nine studies and pooled five randomised controlled trials. Men taking E. longifolia showed a significant increase in total testosterone compared with control, and the effect held in the subgroup who began with clinically low testosterone. The authors’ own conclusion is worth keeping: this supports possible use, and more research is required before it belongs in clinical practice.

Two caveats deserve equal billing. The pooled effect carried a wide confidence interval, which is what happens when you combine five small trials instead of running one large one. And those trials used standardised root extracts at daily doses many times larger than the milligram amounts printed beside Tongkat Ali on blended labels — a gap we examine in our comparison of single-ingredient products versus multi-ingredient blends.

Horny goat weed and icariin: is there human evidence?

Horny goat weed is the common name for Epimedium, a genus whose signature compound, icariin, behaves in laboratory work as a weak inhibitor of the PDE5 enzyme — the same enzyme targeted, far more potently, by prescription erectile dysfunction drugs. The mechanism is real. It is also, so far, a mechanism in cells and animals rather than a demonstrated effect in men.

The best context comes from a urology team at the University of Miami, who catalogued the ingredients in the sixteen most popular testosterone supplements and the sixteen most popular erectile dysfunction supplements sold online in the United States. Horny goat weed was among the most common ingredients they found. Across 37 ingredients and 105 randomised trials, only 19% of ingredients earned a top grade for strong positive evidence, while 68% received C or D grades for contradictory, negative or lacking evidence. Horny goat weed sits in that lower band: a buyer who believes it has been shown to improve erections in men is believing something the published human literature does not yet say.

Is saw palmetto a testosterone ingredient? No, and here is what it does

Saw palmetto (Serenoa repens) is a berry extract studied for lower urinary tract symptoms caused by an enlarged prostate, not for testosterone, libido or erections. It appears on male-vitality labels because prostate health and men’s health have blurred together in marketing, not because it does the job the front of the bottle implies.

It is also the most rigorously tested botanical here, which makes its result unusually informative. An updated Cochrane review published in 2024 pooled 27 studies covering 4,656 men and concluded that Serenoa repens alone provides little to no benefit for men with urinary symptoms due to benign prostatic enlargement, at high certainty of evidence, with little to no difference in quality of life. Adverse events were also little different from placebo, so the safety picture is reassuring even where the efficacy picture is not. When a large, well-conducted review says little to no difference, the honest thing is to repeat it — the same standard we apply in our look at how the leading testosterone boosters compare on dose transparency.

Nettle: leaf on the label, root in the trials

Nettle (Urtica dioica) is a prostate-comfort botanical with one surprisingly large randomised trial to its name, and one label detail most buyers never notice.

The trial is a six-month, double-blind, placebo-controlled crossover study in 620 men with benign prostatic hyperplasia. By intention-to-treat analysis, 81% of men on nettle reported improved urinary symptoms versus 16% on placebo, with the International Prostate Symptom Score falling from 19.8 to 11.8 against 19.2 to 17.7 on placebo. Two results from the same study matter just as much in the other direction: serum PSA and serum testosterone were unchanged in both groups. Nettle did not move testosterone.

The detail worth checking is which part of the plant you are buying. That trial, and the wider prostate literature, uses nettle root. Many male-vitality labels — Vigorpeak’s included — list nettle leaf, a different preparation with a thinner evidence base. A label that says leaf cannot claim the root’s trial.

Does boron raise testosterone?

Boron is an essential trace mineral, and the claim that it raises testosterone traces back to nutritional deprivation experiments from the 1990s rather than to a modern trial in healthy men.

In the best-known of those studies, twelve postmenopausal women were fed a very low-boron diet for 119 days and then given 3 mg of supplemental boron daily for 48 days. The supplementation reduced urinary calcium and magnesium excretion and elevated serum 17-beta-estradiol and testosterone. That is a real finding in depleted postmenopausal women, in a deprivation-and-repletion design, at a defined 3 mg dose of elemental boron. Restoring a nutrient in someone short of it is not the same as raising it in someone who was not, and most men eating a normal diet are not boron-deprived. Note too that 20 mg of a boron amino acid chelate is not 20 mg of boron: a chelate is a compound, and the elemental boron is a fraction of its weight, a figure the panel usually does not print.

Wild yam and sarsaparilla: what the labels imply and what the body can do

Wild yam and sarsaparilla are steroidal-saponin plants, and the reason they appear on hormone-adjacent labels is a chemistry fact that does not transfer to human physiology. Wild yam contains diosgenin, a saponin chemists have used since the 1940s as an industrial starting material for semi-synthetic steroid hormones. That conversion happens in a factory, across several deliberate reaction steps; the human body does not perform it. Swallowing diosgenin does not manufacture progesterone, DHEA or testosterone inside you. Sarsaparilla tells a similar story through sarsasapogenin, with a long traditional record and essentially no controlled human data for male hormone or sexual outcomes.

The fair description of both: traditional botanicals with a plausible-sounding chemistry story and no human evidence behind the hormonal implication. That is not a claim that they do nothing — it is the less flattering statement that nobody has shown they do something.

Studied dose versus label dose, ingredient by ingredient

Ingredient	What the human evidence supports	What the panel prints
Tongkat Ali (Eurycoma longifolia)	Increased total testosterone across five pooled RCTs in a 2022 meta-analysis	10 mg of a 100:1 extract
Horny goat weed (Epimedium)	Laboratory PDE5 activity for icariin; human trial evidence lacking	8 mg of a 10:1 extract
Saw palmetto berry	Little to no benefit for urinary symptoms in a 2024 Cochrane review; not a testosterone ingredient	20 mg
Nettle leaf	Trials used nettle root, which improved urinary symptoms but left testosterone unchanged	20 mg
Boron amino acid chelate	3 mg of elemental boron altered hormone markers in depleted subjects	20 mg of chelate, elemental amount unstated
Wild yam root	Diosgenin is a laboratory precursor; no human hormonal conversion	20 mg
Sarsaparilla root	Traditional use; no controlled human data for male outcomes	20 mg

Read down that third column and the pattern is hard to miss: the amounts printed on a blended male formula sit a long way below the amounts used in the trials that gave these ingredients their reputations. That gap is the most useful thing a buyer can learn to spot, and it is the same gap we trace through the ashwagandha trial doses and the L-citrulline and ginseng blood-flow literature.

Common mistakes when reading a male-formula label

Four errors account for most disappointed purchases, and all four are avoidable in about ninety seconds with the panel in front of you.

Mistaking an extract ratio for a dose. Ten milligrams of a 100:1 extract is not 1,000 mg of root. The ratio describes how the raw material was concentrated, not how potent the capsule is, and ratios are not standardised between manufacturers.

Assuming the plant part does not matter. Nettle leaf against nettle root is the clearest case, but the same trap applies to berry versus seed and root versus aerial parts across the category.

Assuming prostate equals testosterone. Saw palmetto and nettle are prostate-comfort ingredients whose trials measured urine flow and symptom scores. The largest nettle trial measured testosterone explicitly and found no change.

Treating ingredient evidence as product evidence. The Miami review’s most quotable line is that no whole supplement product had published randomised trial evidence. Every claim about a blend is inherited from studies of its parts. A pharmacist reading the same label would start here, and would ask what else you take before you swallow the first capsule.

How to use this when you are comparing products

Start from your complaint, not the ingredient list, because these seven actives do at least three unrelated jobs. For drive and energy, Tongkat Ali is the only one with randomised human data pointing that way. For urinary comfort, saw palmetto and nettle are the relevant names, and for saw palmetto the honest answer is that a large review found little benefit. For erections specifically, none of the seven is the ingredient class with the best data. That triage is the point of matching a formula to your main complaint rather than buying the longest ingredient list. Then check three things on the panel — the amount beside each active, whether the plant part is named, and whether anything hides inside a proprietary blend — and run the shortlist past the known side effects and medication interactions of male supplements before you start.

Frequently asked questions

Which of these ingredients has the best human evidence?

Tongkat Ali. A 2022 systematic review and meta-analysis pooled five randomised controlled trials and found a significant increase in total testosterone in men taking Eurycoma longifolia, with the effect confirmed in men who started with low testosterone. The trials were small and the confidence interval wide, and the authors say more research is needed before clinical use, but it is the only one of the seven actives with that level of support.

Does saw palmetto boost testosterone?

No. Saw palmetto has been studied for lower urinary tract symptoms from an enlarged prostate, not for testosterone, and an updated Cochrane review of 27 trials in 4,656 men concluded it provides little to no benefit even for the urinary symptoms it was tested against. It appears on male-vitality labels because prostate health and men's health are marketed together, not because it changes hormone levels.

Is horny goat weed proven to help erections?

Not in humans. Icariin, the signature compound in Epimedium, acts as a weak PDE5 inhibitor in laboratory work, which is a plausible mechanism. But a systematic review of the ingredients in the most popular male supplements found that most of them, horny goat weed included, sit in the lower evidence grades for contradictory, negative or absent randomised trial data. The mechanism is real; the human proof is not there yet.

Why does nettle leaf appear on labels instead of nettle root?

They are different raw materials with different costs and different evidence. The randomised trials in benign prostatic hyperplasia used nettle root extract, including a 620-man crossover study that improved urinary symptom scores while leaving testosterone unchanged. Nettle leaf has a separate traditional use and a much thinner clinical record, so a label that says leaf cannot fairly borrow the root's trial results.