Stinging Nettle

Urtica dioica L. belongs to Urticaceae, the nettle family, in the order Rosales; NCBI Taxonomy files it as taxon 3501 under the common name great nettle. MSKCC describes it as a perennial herbaceous flowering plant native to Asia, Europe, and North America, and it is one of the most familiar plants of field edges, ditches, gardens, and farmyards, favouring rich, disturbed ground. It spreads by creeping roots and rhizomes into dense clumps of upright stems, with opposite, heart-shaped, coarsely toothed leaves and drooping tassels of tiny green flowers. The species name dioica, “two houses”, refers to male and female flowers usually being borne on separate plants. The EU monographs cover it together with the small annual nettle, Urtica urens L., and their hybrids.

The sting comes from hollow hairs on the leaves and stems. Each is a fine needle with a brittle tip that breaks on contact, letting the hair inject a small amount of irritant fluid into the skin. EMA’s assessment report lists small amounts of histamine, choline, acetylcholine, and serotonin, particularly in the stinging hairs, and the textbook explanation has long credited these amines and formic acid with the burning. Fu and colleagues (Annals of Botany 2006) complicated that story: in the hairs of a related Asian species, Urtica thunbergiana, histamine, oxalic acid, and tartaric acid were the main constituents, serotonin and formic acid were present only at low levels, and oxalic and tartaric acids produced long-lasting pain in rats. Whether the same is true of U. dioica has not been shown.

Two very different materials reach the market. Nettle herb or leaf is the dried aerial parts. EMA’s assessment report, citing older handbooks, describes it as rich in minerals including calcium, potassium, silicon, iron, and magnesium, with flavonoid glycosides of kaempferol, isorhamnetin, and quercetin, triterpenes and sterols including β-sitosterol, and the coumarin scopoletin. Nettle root, defined by the European Pharmacopoeia as the dried underground parts, contains a small lectin called Urtica dioica agglutinin (UDA, 0.05–0.6%), lignans, polysaccharides, sterols, and other compounds. EMA notes that none of these has been established as the active principle, and that phytosterols, often credited in supplement marketing, make up only about 0.01% of nettle products. Extracts differ widely: the EU root monograph lists seven preparations, from a simple tea to dry extracts concentrated as much as 16:1.

Nettle has been a medicine and a food for as long as people have lived beside it. EMA’s assessment report notes that the ancient Greeks knew its effects and that Dioscorides regarded the herb as a tonic, diuretic, digestive, blood purifier, cough remedy, styptic to stop bleeding, and aid to healing wounds; Pliny and later writers also praised it as a styptic, and Dioscorides remained the main authority on nettle into the sixteenth century. Folk medicine across Europe used the herb for dropsy (fluid retention), rheumatism, gout, skin eruptions, poor milk supply, and heavy bleeding, and Sebastian Kneipp promoted it in 1891 as a metabolic enhancer. Stinging the skin over painful joints with fresh nettles is an old practice too; Randall and colleagues noted numerous published references to nettle sting for arthritis pain before they tested it.

The root came later. EMA’s root assessment report says it was first mentioned as a medicine by Paracelsus and Matthiolus, and that in folk medicine the herb and leaves mattered more than the root. The Eclectic physicians used leaf and root as a blood purifier, styptic, tonic, and diuretic. Nettle root was first used for urinary tract disorders in the 1950s, and in 1986 Germany’s Commission E approved it for urination problems in early-stage benign prostatic enlargement. Root extracts, especially a dry extract made with 20% methanol, were on the German market from the 1970s, and four large observational studies there enrolled more than 14,000 men, all reporting significant improvement in symptoms but without a placebo group for comparison.

The modern evidence base grew out of that market. EMA counts more than 17,000 men treated with nettle root preparations in 34 clinical studies, most of them open and uncontrolled. Randomized trials were run in Germany, Russia, and Iran, including trials of a fixed combination of saw palmetto and nettle root extracts. Nettle also entered clinical research on hay fever, in Mittman’s small 1990 trial at a naturopathic college in Portland, Oregon, and arthritis pain, in Randall’s 2000 trial at the University of Plymouth. The EU’s Committee on Herbal Medicinal Products first adopted monographs on nettle herb in 2008, nettle leaf in 2010, and nettle root in 2012, and revised the herb and root monographs on 22 January 2025, granting traditional use only.

How nettle root might act on the prostate is unknown. Chrubasik and colleagues (Phytomedicine 2007), in a comprehensive review, concluded that only a few components of the active principle have been identified and the mechanism remains unclear. They judged it likely that sex hormone binding globulin (SHBG), aromatase, epidermal growth factor, and prostate steroid membrane receptors are involved, and less likely that the root acts on 5-alpha-reductase, the target of finasteride, or on androgen receptors. Extracts and a polysaccharide fraction showed anti-inflammatory activity, and a methanolic extract inhibited cell proliferation in the laboratory. In small human studies summarized by EMA, root extract lowered SHBG levels without significantly changing testosterone or other sex hormones, and Safarinejad found PSA and testosterone unchanged after six months. EMA concludes it is unclear whether the laboratory and animal data predict effects in people.

For the leaf, EMA describes a diuretic effect in animals that is only partly explained. Early studies found more urine with increased chloride and urea, and flavonoids and the high potassium content have been suggested as contributors. But in rats a clear diuretic and blood-pressure-lowering effect appeared only when an extract was infused into a vein, while oral doses in several studies produced little or no effect, so EMA judges the findings of limited relevance to people. In the laboratory, nettle extract blocked the histamine H1 receptor and inhibited COX-1, COX-2, and prostaglandin D2 synthase, enzymes in inflammatory pathways relevant to hay fever (MSKCC). Nettle phenolic compounds also inhibited the carbohydrate-digesting enzymes alpha-glucosidase and alpha-amylase in vitro, a proposed basis for effects on blood sugar.

Deliberate stinging works as a counter-irritant. The injected irritants cause burning, itching weals that, according to Fu and colleagues, can last more than 12 hours. The idea behind applying fresh nettle to a painful joint is that this local irritation dampens the perception of deeper pain, a principle shared with other counter-irritants such as capsaicin creams, but the mechanism has not been studied directly in people using nettle.

Prostate symptoms are the root’s main use, and the evidence is contested. Schneider and Rübben (Urologe A 2004) gave 246 men 459 mg of a dry methanolic root extract or placebo daily for a year. The International Prostate Symptom Score (IPSS) fell from 18.7 to 13.0 with nettle and from 18.5 to 13.8 with placebo, a statistically significant difference, but peak urine flow and residual urine improved about equally in both groups, and the authors wrote that a strong increase in flow should not be expected. EMA’s assessors noted that a 31% versus 25% fall in symptom score is not clinically significant. Smaller German trials from the 1980s and 1990s, with 40 to 72 men each, gave mixed results that EMA judged unconvincing because of small size, short duration, poorly defined outcomes, or unbalanced groups.

The most positive single trial is also the hardest to interpret. Safarinejad (Journal of Herbal Pharmacotherapy 2005) randomized 620 men in Iran to nettle root or placebo for six months. The IPSS fell from 19.8 to 11.8 with nettle and from 19.2 to 17.7 with placebo, peak flow rose by 8.2 versus 3.4 ml per second, residual urine halved, and prostate volume shrank modestly, with no side effects reported. Those effects are far larger than in other trials, and EMA declined to rely on the study because the preparation could not be identified. Combination products have somewhat firmer support: Lopatkin and colleagues (World Journal of Urology 2005) randomized 257 men to a capsule of 160 mg saw palmetto extract plus 120 mg nettle root extract twice daily or placebo for 24 weeks, and symptom scores fell by 6 versus 4 points. Because saw palmetto is in the mix, that trial cannot show what nettle contributes. Chrubasik and colleagues concluded that the size and significance of any effect of nettle root remained to be established before it could be accepted in BPH guidelines.

Hay fever: Mittman (Planta Medica 1990) randomized 98 people with allergic rhinitis to a freeze-dried nettle preparation or placebo for one week; 69 finished. Nettle was rated higher than placebo in the global assessment at follow-up but only slightly higher in daily symptom diaries. Bakhshaee and colleagues (Iranian Journal of Pharmaceutical Research 2017) gave 74 people with allergic rhinitis 150 mg tablets of nettle root extract or placebo for a month; only 40 completed, symptom scores improved in both groups, and the authors acknowledged that placebo produced similar effects, although nasal eosinophil counts fell with nettle. MSKCC’s summary is blunt: evidence is lacking to support nettle for allergies. The popular idea of nettle as a natural antihistamine rests on laboratory findings rather than convincing trials.

Joint pain: Randall and colleagues (Journal of the Royal Society of Medicine 2000) ran a double-blind crossover trial in 27 people with osteoarthritis pain at the base of the thumb or index finger. Applying fresh stinging nettle leaf to the painful area daily for a week reduced pain and disability scores more than white deadnettle (Lamium album), a non-stinging lookalike used as placebo. It was a small trial, and keeping people blind is difficult when one leaf stings. EMA accepts oral nettle herb only as a traditional product for minor articular pain, noting that the available studies are open and uncontrolled. Blood sugar: Ziaei and colleagues (Phytotherapy Research 2020) pooled eight trials with 401 people with type 2 diabetes and found fasting glucose about 18 mg/dL lower with nettle, but no significant change in HbA1c, insulin, or insulin resistance, with very high heterogeneity between studies. That is not a reason to use nettle in place of diabetes treatment.

EU traditional use, nettle root (EMA/HMPC/322646/2023, revision 1, adopted 22 January 2025): for relief of lower urinary tract symptoms related to benign prostatic hyperplasia in adult men, after serious conditions have been excluded by a doctor. Options include 2 g of comminuted root in 150 ml of water as an infusion two to three times daily; a dry extract (DER 7–14:1, methanol 20%) at 150–160 mg three times daily, 300 mg twice daily for the first three months, or 460 mg once daily; a dry extract (DER 5.4–8.3:1, ethanol 20%) at 240 mg three times daily; or a 1:1 liquid extract (ethanol 30%) at 40 drops three times daily. Long-term use is possible. There is no relevant use under 18. See a doctor if symptoms worsen or if fever, spasms, blood in the urine, painful urination, or urinary retention occur.

EU traditional use, nettle herb (EMA/HMPC/261302/2022, revision 1, adopted 22 January 2025). To increase urine in minor urinary complaints, together with plenty of fluid: 1.5 g of dried herb in 150 ml of boiling water as an infusion three to four times daily, for adults; or, from age 12, powdered herb at 380–570 mg three to four times daily or expressed fresh juice at 10–15 ml three times daily. See a doctor if symptoms last longer than two weeks. For minor joint pain in adults: 3–6 g of herb in 200 ml of boiling water three times daily, or juice, liquid extract, or tincture (1:5, 2–6 ml up to three times daily); see a doctor if symptoms last longer than four weeks, and have joints that are swollen, red, or feverish examined. For seborrhoeic skin conditions: 275 mg of powdered herb three times daily from age 12.

Wear sturdy gloves to harvest fresh nettles, and avoid gathering from roadsides or sprayed field margins. Choose medicinal products that state the plant part (leaf, herb, or root), the extract type, and the dose; a capsule labelled simply “nettle” may contain either part, and the two are used for different things. Root products sold for prostate health are often combined with saw palmetto, pygeum, or other ingredients, as MSKCC notes, which changes both the evidence and the risks. Nettle root does not replace monitoring of an enlarged prostate by a doctor.