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Evidence rating: Moderate — two of the five ingredients have controlled human trials with positive results, but the trials are small and one key ingredient failed against placebo
What Red Boost Claims To Be
Red Boost is marketed to men for vitality, blood flow, and sexual performance. The organizing idea is nitric oxide: erections are fundamentally a vascular event, dependent on nitric oxide relaxing smooth muscle in penile blood vessels. Support that pathway nutritionally, the reasoning goes, and you support the function that depends on it.
The mechanism is legitimate physiology — it is the same pathway that prescription PDE5 inhibitors act on, from a different angle. Whether a supplement moves it enough to matter is a separate question, and one the research below actually addresses.
What’s Actually In It
Five named ingredients:
- L-citrulline DL-malate
- Icariin (from horny goat weed, Epimedium)
- Tongkat ali (Eurycoma longifolia)
- Fenugreek (Trigonella foenum-graecum)
- Nettle root
Amounts per ingredient are not disclosed. The powder version lists a scoop of roughly 4.13 g across 30 servings, which at least tells you the total mass available — a useful data point, since the trials below used doses ranging from 200 mg to 1.5 g for single ingredients.
What The Research Shows
According to PubMed, this is a formula where the biochemistry is well established and the clinical evidence is real but preliminary.
L-citrulline has direct human data for erection hardness. In a study of 24 men with mild erectile difficulty (mean age 56.5), participants took placebo for one month, then 1.5 g of L-citrulline daily for a second month. Erection hardness scores improved from 3 to 4 — the score representing normal function — in 50% of men on citrulline versus 8.3% on placebo. Reported monthly intercourse frequency rose from 1.37 at baseline to 2.3 on treatment, and no adverse events occurred. DOI
Read the limitations with the result, though. This was single-blind, not double-blind. It enrolled 24 men. Placebo always ran first rather than being randomized. And the authors state plainly that citrulline is less effective than PDE5 inhibitors, positioning it as an option for men who are wary of those drugs — not as an equivalent.
The pharmacology behind citrulline is sound. A review of nitric-oxide-supporting supplements explains why citrulline is the smarter choice over L-arginine here: oral arginine is largely destroyed by presystemic metabolism before it reaches circulation, while citrulline escapes that and is converted to arginine downstream, then to nitric oxide. DOI
Tongkat ali improved erectile function in a six-month randomized trial — with an important asterisk. A double-blind, placebo-controlled, four-arm trial in 45 men (mean age 47) with age-related androgen decline tested 200 mg of Eurycoma longifolia and a concurrent exercise program, alone and together, over six months. Erectile function improved in both intervention arms, with the largest gains in men receiving supplement plus training, and total testosterone rose. DOI
The authors identify the design flaw themselves: there was no arm receiving only tongkat ali and no arm receiving only training, which makes the two contributions hard to separate cleanly.
Across the wider tongkat ali literature, results are genuinely split. A systematic review of human clinical studies screened 150 articles and included 11 meeting criteria. Seven found a meaningful association between Eurycoma longifolia and improvement in male sexual measures — and four failed to demonstrate sufficient effect. DOI30010-9) A roughly two-thirds hit rate in small trials is encouraging but is not the settled science the category’s advertising implies.
Fenugreek largely did not beat placebo. This is the finding that cuts hardest against the formula. In a double-blind randomized controlled trial, 95 men aged 40-80 took 0, 600, 1200, or 1800 mg of a fenugreek extract daily for 12 weeks. Plasma total testosterone and free testosterone index rose significantly compared to each man’s own baseline — but not significantly compared to placebo (9.0%, p = 0.122 and 11.3%, p = 0.059). Salivary testosterone did beat placebo at the top dose. Critically, the investigators observed no subjective effects at all, on libido or otherwise. DOI
The baseline-versus-placebo distinction is exactly the trap that supplement marketing exploits: “increased testosterone by 13%” is technically true of this trial and thoroughly misleading, because the placebo group moved too.
The Honest Verdict
What holds up: The nitric oxide rationale is real physiology, and L-citrulline is the correct compound to use for it — the choice reflects actual pharmacokinetics rather than label appeal. Citrulline and tongkat ali both have controlled human trials reporting improvements in erectile function scores, and both showed good tolerability. Icariin, the active from horny goat weed, has documented PDE5-inhibiting activity in laboratory work, which is at minimum a coherent reason for its inclusion.
What doesn’t: The trials are small — 24 men, 45 men — with design weaknesses their own authors flag. Fenugreek’s best available RCT found no significant advantage over placebo on plasma testosterone and no subjective benefit whatsoever. A third of the tongkat ali studies found nothing. And the dosing is undisclosed: the citrulline trial used 1.5 g of a single ingredient, while an entire 4.13 g scoop here has to cover five. Nettle root, meanwhile, has essentially no erectile-function evidence; its research base is in prostate symptoms, a different claim entirely.
Who this makes sense for: A generally healthy man with mild, occasional difficulty who wants to try a low-risk nutritional approach, understands the effect will likely be modest, and is not substituting it for a medical evaluation.
Who should skip it: Anyone with more than mild difficulty — persistent erectile dysfunction is frequently an early warning sign of cardiovascular disease or diabetes, and treating it with a supplement can mean missing something that matters far more than the symptom. It also warrants real caution for anyone on nitrates or blood pressure medication, since nitric-oxide-boosting compounds can compound hypotensive effects. See a doctor first; this is one of the clearest cases in the supplement world where the underlying cause is the actual issue.
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This article is for informational purposes only and is not medical advice. Dietary supplements are not intended to diagnose, treat, cure, or prevent any disease. These statements have not been evaluated by the Food and Drug Administration. Talk to your physician before starting any supplement, especially if you have a diagnosed condition or take medication.
Research cited via PubMed:
- Cormio L, et al. Urology. 2011;77(1):119-22. DOI
- Kiani AK, et al. J Prev Med Hyg. 2022;63(2 Suppl 3):E239-E245. DOI
- Leitão AE, et al. Maturitas. 2021;145:78-85. DOI
- Thu HE, et al. Chin J Nat Med. 2017;15(1):71-80. DOI30010-9)
- Lee-Ødegård S, Gundersen TE, Drevon CA. PLoS One. 2024;19(9):e0310170. DOI