Supplements

Stinging Nettle

Updated · 28 sources

Stinging nettle (Urtica dioica, and the related Urtica urens) is a common plant whose root and leaf are sold as different herbal products. The root is used for urinary symptoms from an enlarged prostate (benign prostatic hyperplasia, BPH), and it appears in “free testosterone” supplements. The leaf is used for joint pain and allergies and as a remedy to increase urine flow.

Two facts matter most. First, in January 2025 the European Medicines Agency’s herbal committee reviewed the root trials and concluded that efficacy in BPH “has not yet been proven sufficiently,” so the root is accepted in the EU only as a traditional herbal medicine (EMA assessment report, root, 2025). Second, the testosterone claim rests on lab studies of binding to sex hormone-binding globulin (SHBG). In men with BPH, testosterone did not change significantly.

This page summarizes what EU regulators, clinical trials and meta-analyses report. It is for education only and is not medical advice.

Property Detail
Type Herbal preparation; plant parts differ in constituents and use
Route Oral (tea, extract, juice); fresh leaf applied to skin in one small trial
EU root monograph doses Dry extracts about 301–720 mg/day depending on the extract (960 mg/day at the start for one extract); or 2 g of root as tea, 2–3 times daily
Doses in cited trials Root extract 360–1,200 mg/day; leaf extract 500 mg every 8 hours
Half-life Not established; the EMA lists no pharmacokinetic data for root preparations
Serum testosterone No significant change in controlled BPH trials; no trials found in healthy men or lifters
EU status Traditional herbal medicine only (root, leaf and aerial parts); no well-established use
US status Dietary supplement; limited to “structure and function” claims
WADA status Not named on the 2026 Prohibited List

What it is

Nettle is a perennial plant covered in stinging hairs. On contact, the hairs release active substances that cause itching, skin inflammation and hives within moments. These include small amounts of acetylcholine, serotonin, formic acid and leukotrienes (EMA assessment report, leaf, 2010).

Root vs leaf

The EMA assesses root, leaf and aerial parts separately. A result for one part should not be assumed to apply to another.

Feature Root Leaf
Main constituents named by the EMA Lectin UDA (Urtica dioica agglutinin, 0.05–0.6%), lignans, polysaccharides; sterols are very low in products (about 0.01%) Flavonoids (1–2%), silicates (1–4%), caffeic acid esters; vitamin K about 0.16–0.64 mg per 100 g
EU traditional-use indication Lower urinary tract symptoms related to BPH, after a doctor has excluded serious conditions Minor joint pain; increasing urine flow in minor urinary complaints
EU monograph doses See facts table; for adult and elderly men Tea 8–12 g/day; dry extracts 450–750 mg per dose, 2–3 times daily
Duration in the monograph Long-term use possible No more than 4 weeks (joint pain) or 2–4 weeks (urinary)
Monograph date Revision 1, January 22, 2025 January 14, 2010; reviewed January 26, 2022, no revision needed

Sources: EU monograph, root, 2025; EU monograph, leaf, 2010; EMA leaf addendum, 2022.

A third EU monograph covers the aerial parts (herb). Its traditional uses are minor urinary complaints, minor joint pain and seborrheic skin conditions (EMA assessment report, herb, 2025).

How it works in the body

The mechanism is unknown. The EMA states that only a few components of the active principle have been identified. SHBG, aromatase, epidermal growth factor and prostate steroid membrane receptors have been discussed as possible targets. The 5α-reductase enzyme and androgen receptors are thought less likely to be involved, which separates nettle from drugs such as finasteride. The EMA adds that it is unclear whether the lab and animal data apply to people (EMA, root, 2025).

Absorption data are almost absent. The EMA found none for root preparations themselves. In patients and healthy volunteers given 20 mg of purified UDA by mouth, 30–50% was excreted unchanged in feces and under 1% appeared in urine. That suggests UDA is very stable in the gut and only partly absorbed. We found no study measuring nettle lignans in human blood after a normal dose of root extract.

Regulatory status

  • EU, root. The 2025 monograph lists seven root preparations, all under traditional use, meaning they are accepted on at least 30 years of use rather than on proof from trials. Its market overview shows German products authorized as “well-established use,” some no longer marketed. The committee still judged the placebo-controlled trials inadequate. A European list entry was not supported because genotoxicity data are lacking (EMA, root, 2025).
  • EU, leaf. In 2010 the assessors called the osteoarthritis studies “poor, not convincing,” which ruled out well-established use (EMA, leaf, 2010). A 2022 review found four relevant new papers, none of which justified a revision (EMA leaf addendum).
  • Combinations. The root monograph does not cover mixtures. Its report does list a saw palmetto and nettle root combination (320 mg and 240 mg/day) marketed in Germany since 1976 (EMA, root, 2025).
  • United States. Nettle is sold as a dietary supplement, limited to non-therapeutic “structure and function” claims (EMA, root, 2025). Manufacturers do not need to prove safety or efficacy before sale (LactMed).
  • Guidelines. The European Association of Urology guideline lists nettle root as a traditional-use product. Its only plant-extract recommendations concern hexane-extracted saw palmetto, not nettle (EAU guidelines).
  • Sport. Nettle is not named on the WADA 2026 Prohibited List.

What the research shows

Testosterone and SHBG

SHBG is a blood protein that binds testosterone and controls how much circulates in free form. The marketing idea is that nettle compounds occupy SHBG and so release more free testosterone; one such compound, DVT, is itself sold as a nutraceutical. The evidence comes in two very different kinds.

Lab studies (not in people):

  • Lignans bind SHBG (in vitro). Most lignans from nettle root bound human SHBG in a binding assay, and the affinity of 3,4-divanillyltetrahydrofuran (DVT) was “outstandingly high” among them (Schöttner et al., Planta Med 1997).
  • That affinity is low next to testosterone (in vitro). In diluted human serum, DVT’s relative binding affinity was 1.5% of testosterone’s. With 1 mM zinc added, binding disappeared. DVT did raise testosterone activity in a cell culture reporter system by displacing it from SHBG (Round et al., J Biol Chem 2020).

These two papers do not conflict: DVT is strong compared with other lignans and weak compared with testosterone.

Human measurements (men with BPH, as summarized by the EMA and in the trial abstract):

Study Who and design Product Hormone finding
Vontobel et al. 1985 50 men; double-blind, controlled; 9 weeks Root extract 600 mg/day SHBG fell (p=0.0005); sex hormones did not change significantly
Fischer and Wilbert 1992 40 men; randomized, double-blind; 6 months Root extract 1,200 mg/day SHBG fell (p under 0.05); sex hormones did not change significantly
Bauer et al. 1988 Open study; 12 weeks Root extract PSA, estradiol, estrone and SHBG changed from baseline (p under 0.05); no further data published, so the EMA could not evaluate it
Safarinejad, J Herb Pharmacother 2005 620 men; randomized, double-blind; 6 months Root fluid extract 120 mg, 3 times daily Testosterone and PSA unchanged in both groups

The hormones tested in the first three studies were testosterone, DHT, estradiol and estrone (EMA, root, 2025). The sources above do not report free testosterone. We found no controlled trial in healthy men, lifters or men with low testosterone, and none measuring muscle mass or strength.

About “unbinding testosterone.” The claim takes a lab binding result and assumes it happens in the body at supplement doses. No study we found shows that DVT reaches a meaningful level in human blood, or that nettle raises free testosterone in men. Older men with BPH showed lower SHBG, but their measured testosterone did not rise.

For similar claims about other ingredients, see Tribulus terrestris, Tongkat Ali and Boron.

BPH: nettle root alone

Symptoms are usually measured with the International Prostate Symptom Score (IPSS, 0–35, higher is worse). The EMA counted eight randomized, double-blind, placebo-controlled trials of root preparations. It accepted none as proof of efficacy.

Trial Men and duration Product Nettle vs placebo Limits
Schneider and Rübben, Urologe A 2004 246; 12 months; multicenter Dry extract 459 mg/day IPSS 18.7 to 13.0 vs 18.5 to 13.8 (p=0.0233); peak flow +3.0 vs +2.9 mL/s (not significant) EMA: a difference of 1 point (−5.7 vs −4.7) is not clinically significant
Safarinejad 2005 620 randomized; 6 months Fluid extract 120 mg, 3 times daily IPSS 19.8 to 11.8 vs 19.2 to 17.7 (p=0.002); peak flow +8.2 vs +3.4 mL/s; prostate 40.1 to 36.3 cc (unchanged on placebo) Largest trial, but EMA could not identify the preparation; called intention-to-treat, yet percentages use the 558 completers
Ghorbanibirgani et al., Iran Red Crescent Med J 2013 100; 8 weeks 300 mg capsules, two capsules twice daily AUA score 26.5 to 2.1 vs 27.85 to 27.85 Letter, not a full report; product undefined; see below
Engelmann et al. 1996 41; 3 months Aqueous extract 3 mL twice daily IPSS −9.5 vs −4.7 (p=0.002) Small and short; product withdrawn because of its taste
Dathe and Schmid 1987 72; 6–8 weeks Extract 600 mg/day Mean flow +1.3 vs +0.2 mL/s; residual urine −40% vs −8%; no clear difference in symptoms No measures of spread reported

Trials without a link are as summarized in the EMA report.

The 2013 result is not credible at face value. A fall of about 24 points in 8 weeks, with no placebo change at all, is far outside the other trials here, where placebo groups improved by about 1.5 to 4.7 points. Note also the pattern: the largest trial of an extract similar to those in the monograph (Schneider and Rübben) showed the smallest gain, while the largest effects came from trials whose products could not be identified.

The EMA also set aside a 12-week trial in 60 men (450 mg/day) because the extract was not defined, and a 40-man trial (Fischer and Wilbert) that it read as a negative result for efficacy. It criticized a 2016 meta-analysis for a poorly described search and for including combination products. The committee’s reasons overall were short duration, few patients, poorly defined preparations and non-EU settings.

BPH: combination with saw palmetto

The most studied mixture is PRO 160/120, with 160 mg of saw palmetto extract and 120 mg of nettle root extract per capsule, taken twice daily.

Study Design and n Comparison Result
Lopatkin et al., World J Urol 2005 Double-blind, multicenter; 257 older men; 24 weeks Placebo IPSS fell 6 vs 4 points (P=0.003, one-tailed)
Sökeland, BJU Int 2000 Subgroup of 431 from a double-blind trial of 543 men with early BPH; 24 weeks Finasteride Peak flow +1.9 vs +2.4 mL/s (P=0.52); more adverse events with finasteride
Ibishev et al., Urologiia 2019 Open, randomized; 102 men with BPH and chronic prostate inflammation; 3 months Saw palmetto 320 mg/day alone Authors favored the combination; the abstract gives no figures

Three cautions apply:

  • No placebo arm against finasteride. Both groups improved, but the trial cannot show how much of that was placebo response.
  • Weak pooled evidence. The 2023 Cochrane review pooled saw palmetto mixtures, not only those with nettle, and found a mean IPSS difference of −2.41 points (95% CI −4.54 to −0.29; 4 studies, 460 men). It rated this low certainty and said the mixtures “may result in little to no difference” (Franco et al., Cochrane 2023).
  • Nettle’s own contribution is unclear. Saw palmetto alone gave little to no benefit in the same review, with high certainty (MD −0.90 points at 3–6 months). An added effect from nettle is possible, but the only direct comparison we found is open-label and reports no numbers in its abstract.

Osteoarthritis and joint pain

The evidence is mostly open, observational or based on mixed products.

Study Design and n Product Result
Randall et al., J R Soc Med 2000 Double-blind crossover; 27 patients with thumb-base or index-finger-base osteoarthritis Fresh nettle leaf on the skin daily for 1 week vs white deadnettle Pain (P=0.026) and disability (P=0.0027) improved more with nettle sting
Jacquet et al., Arthritis Res Ther 2009 Double-blind RCT; 81 patients with knee or hip osteoarthritis; 3 months Fish oil, vitamin E and nettle vs placebo Analgesic use 6.5 vs 16.5 tablets/week (P under 0.001); NSAID use 0.4 vs 1.0 defined daily doses/day (P=0.02)
Überall et al., J Pain Res 2026 Retrospective, propensity-matched registry; 1,073 patients in each group; 12 weeks Nettle leaf extract (Hox alpha, 145 mg capsules) vs over-the-counter NSAIDs Composite of no adverse-reaction dropout plus meaningful pain relief: 96.2% vs 73.2%; adverse-reaction dropouts 2.1% vs 25.2%
Ramm and Hansen 1997 Open, no control group; 8,955 patients; 3 weeks Leaf extract 335 mg, 2 capsules twice daily Rest pain fell about 55%; many patients cut NSAID use

The 1997 study is as summarized in the EMA leaf report.

Each result has a major limit:

  • Randall. Blinding was incomplete, because only one plant stings. The trial tests the sting on the skin, not an oral product.
  • Jacquet. Fish oil and vitamin E make it impossible to credit the nettle.
  • Überall. Patients chose their own treatment, more than half the registry was excluded by matching, and data were self-reported. The authors call it exploratory. It was funded by a grant from Strathmann, a company the EMA report names in connection with another nettle leaf product.

In an open randomized trial of 40 people with acute arthritis, both 50 mg of diclofenac plus 50 g of stewed nettle purée and 200 mg of diclofenac improved C-reactive protein and joint scores, and the authors judged them equally effective. The EMA excluded it from the leaf assessment because it probably concerned the whole herb (EMA, leaf, 2010). We found no large placebo-controlled trial of an oral nettle-only product in osteoarthritis.

Allergic rhinitis

Nettle is widely sold for hay fever, but only two small placebo-controlled trials turned up, and neither shows a clear effect:

  • Mittman, Planta Med 1990. 98 people started and 69 finished a 1-week trial of freeze-dried nettle. It rated higher than placebo on global assessment, but only slightly higher on daily symptom diaries.
  • Bakhshaee et al., Iran J Pharm Res 2017. 74 patients with a positive skin prick test took root extract 150 mg, 4 times daily, or placebo for 1 month, on top of loratadine and saline rinses. Only 40 completed. Symptoms improved in both groups, with similar effects on placebo. Nasal eosinophils fell on nettle and IgE, IL-4 and IL-5 did not change; the only reported lab difference between groups was in interferon-γ (P=0.017).

The EMA did not consider this use, because no product had a 10-year medicinal record for it in the EU (EMA, root, 2025).

Blood glucose

Two meta-analyses in adults with type 2 diabetes agree on fasting glucose and differ on HbA1c (average blood sugar over about 3 months):

Meta-analysis Trials Fasting glucose HbA1c
Ziaei et al., Phytother Res 2020 8 RCTs, 401 participants −18.01 mg/dL (95% CI −30.04 to −5.97) −0.77% (95% CI −1.77 to 0.22); not significant
Tabrizi et al., Mini Rev Med Chem 2022 13 clinical trials −17.17 mg/dL (95% CI −26.60 to −7.73) −0.93% (95% CI −1.66 to −0.17); significant

Tabrizi pooled more clinical trials than Ziaei’s RCT-only set, which may explain the different HbA1c verdicts. Neither found a significant change in insulin. Differences between trials were very large (I² about 93–95% for fasting glucose, where 100% means nearly all variation is between studies).

One placebo-controlled trial gave 46 patients with advanced type 2 diabetes a leaf extract, 500 mg every 8 hours for 3 months, on top of oral drugs, and compared them with 46 on placebo. Fasting glucose, 2-hour glucose and HbA1c all improved, without significant changes in creatinine, liver enzymes or blood pressure. The EMA reviewed this and related trials in 2022. It noted short duration, small samples, uncontrolled diets, unspecified background drugs and poorly described extracts, and concluded they did not change its assessment (EMA leaf addendum).

These data apply to people with diagnosed diabetes. We found no evidence on glucose in healthy lifters or on diabetes outcomes such as complications.

Blood pressure

Human data are limited and inconsistent:

  • Type 2 diabetes. Tabrizi found systolic pressure 5.03 mmHg lower (95% CI −8.15 to −1.91), with no significant change in diastolic pressure (Tabrizi et al., 2022). The 92-patient leaf extract trial above found no significant effect (EMA leaf addendum).
  • Mild hypertension. In a Lebanese trial, 8 people drank a nettle leaf extract (300 mL/day) for 16 weeks. Systolic pressure fell from 138.53 to 126.64 mmHg, against 137.41 to 136.77 mmHg in 7 people on placebo. The paper describes the groups as randomized but also as formed by taste preference, and the extract was not chemically characterized (Samaha et al., Biomolecules 2019).
  • Urine output and animal data. In an open study of 32 adults with heart or venous insufficiency, 15 mL of nettle herb juice 3 times daily raised urine volume, which the EMA did not accept as proof. In anesthetized rats, intravenous extract increased urine output and lowered blood pressure. The EMA says that in its animal data the diuretic effect was shown only this way, with limited relevance to people (EMA, herb, 2025).

Side effects and risks

Reported side effects

The EU monographs list stomach and bowel complaints (nausea, heartburn, fullness, gas, diarrhea, and vomiting with the leaf) and allergic reactions (itching, rash, hives), at unknown frequency.

  • Root. More than 17,000 men took part in 34 clinical studies, with few adverse effects reported. The EMA derived no safety concerns from EudraVigilance, the EU’s side effect database, and cites more than 30 years on the market. In the one-year Schneider and Rübben trial, events were 29 on nettle and 38 on placebo (EMA, root, 2025).
  • Leaf. In 5 studies totaling 10,368 patients on a dry extract for 3 weeks to 12 months, minor effects occurred in 1.2–2.7%, with no serious events reported (EMA, leaf, 2010).

Skin contact

Handling the fresh plant causes a local rash and itching. In the thumb pain trial, 23 of 27 patients found the sting acceptable. One stopped because of a rash on the hand (EMA, leaf, 2010).

Breast effects: case reports only

Two reports link nettle to breast symptoms. They cannot establish cause or frequency.

  • Nettle tea. A man developed gynecomastia (breast tissue growth) and a woman developed galactorrhea (milk discharge), with nettle tea the only cause identified (Sahin et al., N Z Med J 2007).
  • Nettle supplement. A 30-year-old woman taking 500 mg for allergies developed galactorrhea with normal prolactin and thyroid tests. It resolved within a week of stopping. She was also using an etonogestrel implant and occasional echinacea (Easton et al., Am J Case Rep 2021).

The proposed link to SHBG and estrogen is hypothetical. The relevant controlled trials did not report significant changes in sex hormones.

Pregnancy and breastfeeding

Human safety data are lacking. The leaf and herb monographs say use in pregnancy and lactation is not recommended, and no fertility data exist. The EMA notes that nettle is reputed to be an abortifacient and to affect the menstrual cycle, and that effects on the uterus have been documented in animals (EMA, herb, 2025). The root monograph marks pregnancy as “not relevant” because it covers only men with BPH. That is not a statement of safety, and its report says use cannot be recommended (EMA, root, 2025).

LactMed describes nettle as a purported milk-increasing herb with minimal scientific support. It advises against applying it to the breast, after one infant developed an allergic rash following topical use on the mother’s nipple (LactMed).

Drug interactions

All three monographs state “none reported,” but this reflects an absence of studies as much as evidence of safety. The EMA has no pharmacokinetic or interaction data for the root.

  • Warfarin and similar anticoagulants. German labeling warned that vitamin K in nettle leaf could weaken these drugs. The EMA calculated 24–96 mcg of vitamin K at the maximum daily dose, under 1% of a therapeutic vitamin K dose, and expects no interaction (EMA, herb, 2025).
  • Diabetes and blood pressure drugs. A reference text warns of possible interactions from excessive use, based on preclinical data. The EMA found this insufficient for a monograph warning. Since the trials above report lower glucose in people on oral diabetes drugs, an additive effect cannot be ruled out, but none has been documented.

Who should be careful

  • Reduced fluid intake. The leaf monograph contraindicates use where reduced fluid intake is advised, such as severe heart or kidney disease.
  • Urinary symptoms. Fever, spasms, blood in the urine, painful urination or urinary retention need medical review. The root is only meant for use after a doctor has excluded serious conditions.
  • Joint swelling. Joint pain with swelling, redness or fever also needs medical review.
  • Children. The leaf is not recommended under 12 years, and the root has no relevant use under 18.
  • Missing safety tests. Adequate genotoxicity, reproductive toxicity and carcinogenicity testing has not been done.

Quality and product variability

“Nettle” on a label does not define a product. Root extracts in the EU monograph vary by solvent (methanol or ethanol at different strengths) and by extract ratio. The EMA could not identify the preparation in several trials, including the largest. LactMed adds that dietary supplements often differ from their labels in ingredients or amounts, and that results for one product may not apply to another.

Key takeaways

  • Root and leaf are different products. The root is used for BPH symptoms; the leaf for joint pain and urine flow. Evidence for one does not carry over to the other.
  • No testosterone effect shown. Binding to SHBG is a lab finding, and DVT has only 1.5% of testosterone’s affinity. In men with BPH, SHBG fell but testosterone did not significantly change, and no trials in healthy men or lifters were found.
  • BPH efficacy is unproven. The EMA accepted root only as a traditional medicine in 2025. The largest trial of a monograph-type extract showed a 1-point IPSS difference, while the largest reported effects came from undefined products.
  • Saw palmetto combinations remain uncertain. A placebo-controlled trial found a 2-point advantage, and Cochrane rated pooled mixture evidence as low certainty.
  • Osteoarthritis, allergy and metabolic data are weak. Trials are small, use mixed or undefined products, or lack controls. Fasting glucose fell about 18 mg/dL in people with type 2 diabetes, but the EMA did not find these trials decisive.
  • Generally well tolerated, with gaps. Stomach upset and allergic reactions are the main known effects. Pregnancy and lactation use is not recommended, and genotoxicity and interactions remain poorly studied.

Sources

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