The science of men's vitality ingredients

The botanicals in men's vitality supplements fall into three honest categories: a few with real mechanistic support, several with promising but thin human evidence, and some that are there for tradition rather than data. Almost no marketing in this category tells you which is which, so this guide does.

The short version. L-citrulline has the clearest mechanism, because it demonstrably raises the precursor your body uses to make nitric oxide. Maca has reasonable evidence for sexual desire and, importantly, works without changing testosterone. Tongkat ali and fenugreek have small positive trials worth taking seriously but not treating as settled. Ginseng has a Cochrane review behind it, with low-certainty conclusions. Horny goat weed has an interesting laboratory mechanism that does not transfer cleanly to humans. Shilajit, cordyceps, and oyster extract are traditional tonics with limited controlled data. Zinc, magnesium, and vitamin D matter, but mostly if you are low in them.

A systematic review in the International Journal of Impotence Research asked whether marketed testosterone boosters actually raise serum testosterone and found that most lacked robust supporting evidence. That is the backdrop for everything below, and it is why the framing here is support rather than transformation.

How to read evidence in this category

Four principles make supplement research far easier to interpret, and they explain most of the disagreement you will encounter.

Repletion beats supplementation. Nutrients produce their clearest effects in people who are deficient. Correcting a low vitamin D level does something measurable. Adding vitamin D to someone already sufficient generally does not. Most of the impressive results in nutritional research come from studies of deficient populations, and they do not generalise to everyone.

Mechanism is not outcome. A compound can do something interesting in a test tube and nothing useful in a person. Absorption, metabolism, and dose all intervene. Laboratory activity is a reason to run a trial, not a substitute for one.

Extract standardisation matters enormously. Two products naming the same plant can contain different amounts of different active compounds prepared different ways. This is a genuine reason trials of the same botanical disagree, and it is also a convenient excuse for brands whose ingredient failed a trial. Treat it as a real factor and a common dodge simultaneously.

Baseline determines response. Botanicals aimed at hormones and vitality consistently show larger effects in men who start lower. A trial in young healthy athletes and a trial in tired 55-year-olds can produce genuinely different results from the same compound.

Circulation support

L-citrulline

This is the ingredient with the strongest mechanistic case in the entire category, and it is not a botanical at all but an amino acid.

Nitric oxide, the molecule that signals blood vessels to widen, is made from L-arginine. Supplementing arginine directly is inefficient, because much of an oral dose is degraded in the gut and liver before it reaches circulation. L-citrulline bypasses that and converts to arginine in the kidneys. A study in the British Journal of Clinical Pharmacology compared both directly and confirmed that oral citrulline raises plasma arginine more effectively than oral arginine, with corresponding effects on nitric oxide metabolism.

That is a solid, replicated pharmacological finding. It supports the pathway. It is not evidence that citrulline treats any condition.

Panax ginseng

Korean red ginseng is among the better-studied botanicals here, partly because it has been examined for sexual function specifically. A Cochrane review of ginseng for erectile dysfunction assessed the trial literature and concluded the evidence was of low certainty, meaning possible benefit but with limitations in trial quality and consistency that prevent a confident conclusion.

Low-certainty evidence from Cochrane is genuinely more than most ingredients in this space can claim. It is still low certainty, and the proposed mechanism, involving nitric-oxide-mediated vasodilation, remains better established than the clinical outcome.

Libido and vitality botanicals

Maca

Maca, Lepidium meyenii, is a Peruvian root with a distinctive and useful evidence profile. A randomised trial in Andrologia found maca improved sexual desire in adult men, and the study title states the key finding plainly: the effect had no relationship with serum testosterone levels.

That matters in both directions. It means maca is not a testosterone booster and should never be sold as one. It also means the observed effect on desire is not explained by hormones, which makes it more interesting rather than less. Separate work by the same group found maca improved semen parameters in adult men.

Trials have generally been small. Typical supplemental doses sit around 1,500 mg to 3,000 mg per day of root powder or extract.

Tongkat ali

Tongkat ali, Eurycoma longifolia, has accumulated a modest but real body of controlled research, much of it on a standardised water extract. A trial in Food and Nutrition Research examined its effects on quality of life, mood, and stress markers, and a later trial in the same journal looked at testosterone levels and quality of life in ageing men.

The proposed mechanisms involve reducing cortisol and supporting free rather than total testosterone. Effects, where reported, tend to appear over 8 to 12 weeks rather than days, and to be larger in men who begin with lower levels. Doses in trials commonly fall in the 200 mg to 400 mg per day range for standardised extracts. The evidence is promising and the trials are small.

Fenugreek

Fenugreek, Trigonella foenum-graecum, appears in this category largely on the strength of trials of specific standardised extracts. A study in The Aging Male examined one such extract in men and reported reductions in symptoms associated with declining androgens alongside changes in testosterone measures. A more recent review in Advances in Clinical and Experimental Medicine assessed fenugreek and ashwagandha together as ingredients in testosterone-boosting supplements and discussed the clinical implications more cautiously.

Fenugreek also affects blood sugar, which is worth knowing if you take medication for diabetes.

Horny goat weed and icariin

This one requires the most care, both scientifically and legally, and the honest account is more interesting than the marketing.

The principal active compound in Epimedium is icariin, and icariin does inhibit phosphodiesterase type 5, the same enzyme targeted by prescription erectile dysfunction drugs. Research in the Journal of Natural Products characterised this activity and showed that chemically modified icariin derivatives can be potent PDE5 inhibitors.

Read that carefully, because the distinction is the whole story. Icariin itself is a far weaker PDE5 inhibitor than pharmaceutical agents, by orders of magnitude. The potent compounds in that research are synthetic derivatives, not what is in a capsule of dried Epimedium. A shared enzyme target does not mean a shared clinical effect, and the gap between a laboratory inhibition assay and a therapeutic dose in a human being is enormous.

So the honest position: interesting mechanism, real traditional use, weak human evidence, and no basis whatsoever for comparing it to prescription medication. Anyone marketing horny goat weed as natural Viagra is misrepresenting the science.

Two safety notes that matter more here than elsewhere. Because PDE5 inhibition affects blood pressure, and because Epimedium products vary widely in content, speak to a doctor before using it if you take nitrates, blood pressure medication, or blood thinners.

Adaptogens

Ashwagandha

Ashwagandha, Withania somnifera, is the most-searched botanical in men's health, and its best-supported effects are on stress and sleep rather than hormones. Its mechanism centres on reducing cortisol.

A randomised controlled trial in the Journal of the International Society of Sports Nutrition examined root extract supplementation alongside resistance training and reported effects on muscle strength and recovery. The 2025 review in Advances in Clinical and Experimental Medicine covers its role in testosterone-focused products with appropriate caution.

Where ashwagandha most plausibly helps a stressed, under-slept man over 45 is by improving sleep and stress, which then supports the hormonal system indirectly. That is a less exciting claim than a direct hormonal one, and it is better supported.

Traditional tonics with thinner evidence

Three ingredients belong in an honest category of their own: long traditional use, plausible rationale, limited controlled human data.

Shilajit is a resinous substance from Himalayan rock, containing fulvic acid and trace minerals, traditionally used in Ayurvedic practice for energy and stamina. Some small studies have examined testosterone and sperm parameters. The systematic review of testosterone boosters cited at the top of this article is the appropriate lens: most such products lack robust evidence. Purity is also a genuine concern with shilajit, since it is a mineral-rich natural material and cheap products have been found contaminated with heavy metals. Sourcing and third-party testing matter more here than for almost anything else in this guide.

Cordyceps, particularly Cordyceps militaris, is studied mainly for exercise performance, oxygen utilisation, and recovery rather than for hormones. A recent review in Nutrients assessed the ergogenic and post-exercise recovery evidence in humans. The picture is modest and mixed.

Oyster extract is essentially a concentrated natural source of zinc, with a long traditional association with male vitality. Its rationale rests on zinc's established role in reproductive health rather than on trials of oyster extract itself.

The micronutrients

Less glamorous than the botanicals, better evidenced, and cheaper.

Vitamin D

Vitamin D is the micronutrient with the most direct evidence linking it to testosterone. A randomised study in Hormone and Metabolic Research examined vitamin D supplementation and testosterone levels in men, finding increases in testosterone measures in men receiving vitamin D compared with placebo.

The critical qualifier is that participants in this line of research were vitamin D deficient or insufficient at baseline. This is repletion, not enhancement, and it illustrates the first principle in this guide precisely. Vitamin D status is cheap to measure, deficiency is common, and testing is more sensible than guessing.

Zinc and magnesium

Both are involved in testosterone production and in hundreds of other enzymatic processes. Deficiency in either is associated with lower testosterone, and correcting a deficiency can help. Taking large doses when you are already sufficient does not produce further benefit, and excessive zinc intake interferes with copper absorption. Food first, supplement to fill an actual gap.

Magnesium is worth a specific mention because a substantial proportion of adults consume less than the recommended intake, according to the NIH Office of Dietary Supplements, and it also supports sleep quality, which feeds back into the hormonal picture.

What this means for choosing a formula

Practical filters, given all of the above:

• Look for standardised extracts with stated doses, not a long list of plant names at unspecified amounts. A proprietary blend that hides doses usually hides small ones.
• Be sceptical of very long ingredient lists. Twenty botanicals in one capsule means each is present below any trialled dose.
• Prefer citrulline to arginine if circulation is the goal, for the reason described above.
• Check third-party testing, particularly for shilajit and any mineral-rich natural material.
• Expect weeks, not days. Every mechanism in this article operates on background physiology.
• Distrust anything compared to prescription medication. That comparison is a marketing tell, not a scientific claim.

Frequently asked questions

Do testosterone booster supplements actually work?

Mostly not, on current evidence. A systematic review in the International Journal of Impotence Research examined whether marketed testosterone boosters raise serum total testosterone and found that most lacked robust supporting evidence. A few ingredients have genuine small trials behind them, and vitamin D repletion in deficient men has reasonable support. But the category as sold is far ahead of the data, and if you suspect low testosterone, a blood test and a doctor will serve you better than a bottle.

Does maca raise testosterone?

No. This is unusually well established for a botanical: the randomised trial in Andrologia that found maca improved sexual desire in men explicitly reported that the effect had no relationship with serum testosterone levels. Maca appears to work through a non-hormonal route. Any brand selling maca as a testosterone booster is contradicting the primary evidence for its own ingredient.

Is horny goat weed like natural Viagra?

No. Icariin, its main active compound, does inhibit PDE5, the same enzyme prescription drugs target, but it is a far weaker inhibitor by orders of magnitude, and the potent compounds in the research literature are synthetic derivatives rather than what is in a capsule of dried Epimedium. Sharing an enzyme target is not the same as sharing a clinical effect. Speak to a doctor before using it if you take nitrates, blood pressure medication, or blood thinners.

How long do these ingredients take to work?

Weeks to months, not days. Every mechanism described in this article acts on background physiology rather than producing an acute effect. Trials of tongkat ali, for example, typically report changes over 8 to 12 weeks. If you are expecting something you can feel the same evening, this is the wrong product category, and the right conversation is with a doctor about on-demand options.

Which single ingredient has the best evidence?

It depends what you mean by best. For a clearly demonstrated mechanism, L-citrulline, because it is directly shown to raise plasma arginine, the precursor for nitric oxide, more effectively than arginine itself. For clinical outcome in a specific area, maca has a randomised trial on sexual desire, and ginseng has a Cochrane review, though with low-certainty conclusions. For the highest-value intervention overall, vitamin D repletion if you are actually deficient.

Should I worry about quality and contamination?

For most botanicals, buy from a company that does third-party testing and states its doses. For shilajit specifically, be genuinely careful: it is a mineral-rich natural material and cheap products have been found contaminated with heavy metals. Third-party testing is not a nice-to-have there.

Can I take these alongside prescription medication?

Ask your doctor or pharmacist first, and be specific about what you want to take. Several interactions in this article are real rather than theoretical: vitamin K opposes warfarin, fenugreek affects blood sugar and so interacts with diabetes medication, and anything with PDE5 activity is a concern alongside nitrates or blood pressure medication. Supplements are not automatically safe just because they are sold without a prescription.

References

1. Morgado A, et al. Do "testosterone boosters" really increase serum total testosterone? A systematic review. Int J Impot Res, 2024. PubMed
2. Schwedhelm E, et al. Pharmacokinetic and pharmacodynamic properties of oral L-citrulline and L-arginine: impact on nitric oxide metabolism. Br J Clin Pharmacol, 2008. PubMed
3. Lee HW, et al. Ginseng for erectile dysfunction. Cochrane Database Syst Rev, 2021. PubMed
4. Gonzales GF, et al. Effect of Lepidium meyenii (MACA) on sexual desire and its absent relationship with serum testosterone levels in adult healthy men. Andrologia, 2002. PubMed
5. Gonzales GF, et al. Lepidium meyenii (Maca) improved semen parameters in adult men. Asian J Androl, 2001. PubMed
6. George A, et al. Efficacy and safety of Eurycoma longifolia water extract plus multivitamins on quality of life, mood and stress. Food Nutr Res, 2018. PubMed
7. Chinnappan SM, et al. Effect of Eurycoma longifolia standardised aqueous root extract on testosterone levels and quality of life in ageing men. Food Nutr Res, 2021. PubMed
8. Rao A, et al. Testofen, a specialised Trigonella foenum-graecum seed extract, reduces age-related symptoms of androgen decrease. Aging Male, 2016. PubMed
9. Skrzypiec-Spring M, et al. Withania somnifera and Trigonella foenum-graecum as ingredients of testosterone-boosting supplements: possible clinical implications. Adv Clin Exp Med, 2025. PubMed
10. Dell'Agli M, et al. Potent inhibition of human phosphodiesterase-5 by icariin derivatives. J Nat Prod, 2008. PubMed
11. Wankhede S, et al. Examining the effect of Withania somnifera supplementation on muscle strength and recovery: a randomized controlled trial. J Int Soc Sports Nutr, 2015. PubMed
12. Jędrejko M, et al. Current evidence of ergogenic and post-exercise recovery effects of dietary supplementation with Cordyceps militaris in humans. Nutrients. PubMed
13. Pilz S, et al. Effect of vitamin D supplementation on testosterone levels in men. Horm Metab Res, 2011. PubMed

Turning ingredients into a routine

Knowing what an ingredient does is only half of it. The other half is dose, sequence and what to leave out, which is covered in what supplements a man over 45 should take. Before adding anything it is worth knowing your baseline, so blood tests men over 45 should ask for is the sensible first step. And if you want the short version of why dose disclosure matters so much in this category, we explain why we print every amount on the label.

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This article is for general education and is not medical advice. It is not a substitute for diagnosis or treatment by a qualified clinician. Speak to your doctor or pharmacist before starting any supplement, particularly if you take prescription medication or have an existing condition.

These statements have not been evaluated by the Food and Drug Administration. These products are not intended to diagnose, treat, cure, or prevent any disease.