Herbal Supplements and Erectile Function: A UK Evidence Guide (2026)

By Jordan Harvey · 26 July 2026 · Updated 26 July 2026 · 13 min read

Erectile difficulties affect a meaningful share of UK men — 41.5% overall in a study of 12,490 participants, rising to 45.6% in men over 40 and approximately 50% in men over 55 (Li et al., Int J Clin Practice, 2022). Since the UK approved over-the-counter sildenafil (Viagra Connect®) in 2018, prescription volume has grown substantially — over 4.7 million ED medications are now dispensed annually across UK ICBs. Sildenafil works for many men, but it isn't for everyone: side effects affect up to 16% of users, it is contraindicated with nitrate medication, and it addresses the immediate symptom rather than the underlying physiology.

This guide reviews the eight herbal ingredients with the strongest published evidence related to erectile function, ranked by trial quality. L-Arginine tops the list: in Rhim et al. (2019), a meta-analysis of 10 RCTs (n=540), L-arginine was associated with statistically significant erectile-function improvement (OR 3.37, p=0.01) at 1,500–5,000mg/day. Tongkat Ali follows closely, with a 5-RCT meta-analysis (SMD 1.352, p=0.001) on serum testosterone. See our herbal vs prescription ED guide for more on how the published evidence for each compares.

How Do Herbal Supplements Differ from Prescription PDE5 Inhibitors?

Sildenafil, tadalafil, and vardenafil are PDE5 inhibitors: they block the enzyme that breaks down cyclic GMP (cGMP), the molecule that keeps blood vessels in the penis relaxed during arousal. They are effective and fast-acting, but they do not address upstream physiological factors such as nitric oxide synthesis, testosterone status, or vascular health. The herbal ingredients reviewed in this article have been studied via three different mechanisms in published research:

• Nitric oxide precursor activity: L-Arginine is the amino acid your body converts into nitric oxide via endothelial NOS (eNOS). Rather than preventing NO breakdown, L-Arginine increases substrate supply. In Rhim et al. (2019), this pathway was associated with improved IIEF scores across 10 RCTs.
• Testosterone status: In Leisegang et al. (2022), Tongkat Ali was associated with significant serum testosterone changes (SMD 1.352). Zinc carries an EFSA-authorised health claim: “Zinc contributes to the maintenance of normal testosterone levels in the blood.” In Pandit et al. (2016), an RCT using purified shilajit at 250mg twice daily (500mg/day), total testosterone was approximately 20% higher than placebo over 90 days. Blue Power contains shilajit at 50mg/day; this finding cannot be transferred to Blue Power as a label claim.
• PDE5-pathway activity (laboratory data): In Dell'Agli et al. (2008), icariin (the active compound in Horny Goat Weed) demonstrated competitive PDE5 inhibition at IC50 0.432 μmol/L with 167-fold selectivity for PDE5 over PDE4. This is the same enzyme class targeted by sildenafil, though icariin's activity is considerably lower. Most evidence for icariin's effects in humans remains preclinical.

This explains the timeline difference. Sildenafil works in 30–60 minutes; herbal ingredients studied in trials generally showed measurable effects after 4–12 weeks of consistent daily use. They are not on-demand. They are not expected to be faster than the underlying biology they may be influencing.

What Are the Side Effects of Sildenafil & Why Some Men Ask About Herbal Supplements?

Sildenafil is contraindicated with nitrate medications (used for angina), and caution is needed with antihypertensives, alpha-blockers, and certain HIV medications. Men who experience persistent side effects, those who cannot take PDE5 inhibitors due to contraindications, or those who want to understand what the published research says about upstream herbal ingredients have legitimate reasons to read an evidence review like this one. None of this means sildenafil is inappropriate — it is an effective medication for many men.

8 Herbal Ingredients Studied for Erectile Function, Ranked by Evidence

1. L-Arginine Strongest Evidence

L-Arginine is the amino acid the body converts into nitric oxide via endothelial NOS (eNOS). In Rhim et al. (2019), a meta-analysis pooling 10 RCTs (n=540), a statistically significant improvement in erectile function was reported (OR 3.37, 95% CI 1.29–8.77, p=0.01) across all four IIEF subdomains (Rhim et al., Andrology, 2019). In studies combining L-Arginine with Pycnogenol (pine bark extract), even stronger effects were observed across multiple RCTs in men with mild-to-moderate erectile difficulty.

Adverse effects in trials: 8.3% in the L-Arginine group vs 2.3% with placebo, mostly mild GI symptoms. Clinical doses used in trials ranged from 1,500 to 5,000mg daily. For depth on the mechanism, dosing nuances, and the L-citrulline comparison, see our L-Arginine guide.

2. Tongkat Ali Studied Ingredient

Tongkat Ali (Eurycoma longifolia) is among the most clinically studied herbal ingredients in this category. In Leisegang et al. (2022), a meta-analysis of 5 RCTs, a significant change in serum testosterone was reported (SMD 1.352, 95% CI 0.565–2.138, p=0.001) (Leisegang et al., 2022). In Leitao et al. (2021), a 6-month RCT, improvements in erectile function scores and total testosterone were observed in men with age-related hormonal decline (Leitao et al., 2021). In a 12-week sexual-function trial, measures of sexual desire increased progressively at weeks 6 and 12 with continued use.

3. Horny Goat Weed (Icariin) Icariin Source

Horny Goat Weed contains icariin, a flavonoid. In Dell'Agli et al. (2008), laboratory work measured icariin's IC50 at 0.432 μmol/L with 167-fold selectivity for PDE5 over PDE4 — the same enzyme class targeted by sildenafil, though at considerably lower activity (Dell'Agli et al., 2008). In animal studies, erectogenic effects were reported with higher nNOS expression and improved smooth muscle content in the corpus cavernosum.

The honest caveat: most evidence for icariin's effects in humans remains preclinical. Enhanced icariin derivatives have shown up to 80-fold greater in vitro activity in laboratory settings, but human RCTs are limited.

4. Korean Ginseng Cochrane-Reviewed

Korean Red Ginseng was the subject of a Cochrane Review (2021) covering 9 RCTs vs placebo. The review found a modest improvement in erectile function on the IIEF-15 (MD 3.52, 95% CI 1.79–5.25) and a notable improvement in self-reported intercourse success (RR 2.55, 95% CI 1.76–3.69), although evidence certainty was rated low (Cochrane 2021). An earlier systematic review of 7 RCTs (n=349) had reported similar effects (RR 2.40, p<0.00001).

5. Maca Root Studied Ingredient

In the published literature, maca has been associated with changes in sexual desire without corresponding changes in testosterone levels — a different mechanism from the testosterone-related ingredients above. In Shin et al. (2010), a systematic review of 4 RCTs, 2 trials showed positive effects on sexual desire, with benefits typically appearing after 6 or more weeks (Shin et al., BMC Comp Alt Med, 2010). One trial also showed improvements in IIEF-5 scores. The mechanism appears to be central nervous system-mediated rather than hormonal.

6. Zinc EFSA-Authorised Claim

Zinc carries an EFSA-authorised health claim: “Zinc contributes to the maintenance of normal testosterone levels in the blood.” (Regulation EU 432/2012, Claim ID 301). In Prasad et al. (1996), zinc restriction reduced serum testosterone significantly in young men, and supplementation in zinc-deficient elderly men was associated with a near-doubling of levels. Since testosterone status relates to vascular and sexual health, adequate zinc is considered foundational. See our Zinc & Testosterone guide for the full evidence breakdown.

7. Shilajit Studied Ingredient

In Pandit et al. (2016), a double-blind placebo-controlled RCT in men aged 45–55, total testosterone was approximately 20% higher than placebo over 90 days in those receiving purified shilajit at 250mg twice daily (Pandit et al., Andrologia, 2016). Blue Power contains shilajit at 50mg/day; the Pandit (2016) finding used 500mg/day and cannot be transferred to Blue Power as a label claim. The fulvic acid content in shilajit has also been studied for its role in mineral absorption — potentially relevant for men over 50.

8. Tribulus Terrestris Weakest Evidence

Tribulus is widely marketed in the men's supplement sector, but the evidence is the weakest in this list. A 2025 systematic review found erectile function improvement in only 3 of 5 studies at 400–750mg/day, and crucially, 8 of 10 testosterone studies found no significant change in androgen profiles (2025 systematic review). Tribulus is not in Blue Power's formula precisely because the evidence does not support inclusion at the same level as the other ingredients above.

Complete Comparison Table

Safety, Interactions & When to See Your GP

Persistent erectile difficulty is often an early warning sign of cardiovascular disease, type 2 diabetes, or other medical conditions. The same vascular biology that drives erections is the biology of arterial health throughout the body — if it is failing in one place, it is worth checking everywhere. Addressing erectile difficulty requires a GP appointment as the starting point, then layering in lifestyle changes (sleep, exercise, alcohol, weight) and supplements as appropriate under professional guidance.

How to Choose Quality Herbal Supplements in the UK

• Avoid hidden "Men's Health Blend" formulas: If individual ingredient milligrams are not disclosed, you cannot compare to clinical evidence.
• Check for sildenafil contamination: The MHRA has issued multiple warnings about "natural" supplements illegally spiked with prescription PDE5 inhibitors. Buy only from UK-registered companies.
• Match doses to clinical evidence: published trials used single-ingredient doses (for example, 200mg Tongkat Ali); a multi-ingredient supplement spreads its content across several ingredients at lower per-ingredient doses. Compare any product's disclosed milligrams against the trial doses listed in the comparison table above.
• UK GMP certification: Required quality baseline.
• Certificate of Analysis: Available on request — confirms identity, active content, and absence of contaminants.
• Read the Mendurance comparison for the broader UK supplement market context.
• Set realistic timelines: 4–12 weeks of daily use is the trial-supported window. If you are expecting same-day results, you need a PDE5 inhibitor and a GP conversation, not a supplement.

What Blue Power Contains

Retail prices vary; figures are indicative of single-ingredient UK high-street pricing.

Frequently Asked Questions

The Bottom Line: What the Evidence Supports

For UK men weighing whether a herbal supplement fits alongside medical advice, the published evidence is worth reviewing ingredient by ingredient, at the trial doses described above. The ranking is clear: L-Arginine and Tongkat Ali have the strongest meta-analytic evidence, Korean Ginseng has Cochrane-reviewed support, and Shilajit, Maca, Zinc, and Horny Goat Weed have each been studied individually in published trials, with evidence of differing strength as set out in the ranked section above. Tribulus and most proprietary blends with undisclosed doses do not make the cut.

Crucially: see your GP first. Erectile difficulty can be an early warning sign of cardiovascular disease, diabetes, or other conditions that need medical assessment. Once underlying issues have been addressed, any decision about a herbal supplement is best made with your GP, reviewing the published per-ingredient evidence and disclosed doses — as a complement to medical care, never a replacement for it.