Stinging nettle usually refers to Urtica dioica, but it can also include a closely related species, Urtica urens, known as garden nettle, and hybrids of these two species. Urtica dioica is an annual native to the temperate regions of Eurasia, now found throughout the world.

Healers from many cultures use nettle branches as part of a whipping technique called flagellation or urtification. Whipping paralyzed limbs and other afflicted or painful body parts supposedly activates the muscles and stimulates the organs. Hot leaf poultices and pounded leaves made from nettle were traditionally used as topical treatments for rheumatic pain. The herb was also historically used to treat uterine hemorrhage (particularly after childbirth) and as a snuff for nosebleeds. Today, nettle root is an effective therapy for treating the symptoms of benign prostatic hyperplasia (BPH).

Stinging nettle (Urtica dioica), or common nettle, is an herbaceous shrub that reaches a height of nearly 3 feet. It prefers nitrogen-rich soil and blooms between June and September. The heart-shaped, finely toothed, tapered leaves are alternate and elliptical. The small green flowers are incomplete, and multiple types of flowers are often found on a single plant. The entire plant, especially the leaves and stem, is sparsely covered with stinging hairs that are painful when touched.

The stings are glandular hairs, or sharp, polished spines. Each hair contains an acrid fluid filled with histamine and formic acid. These chemical substances are released whenever the plant is forcefully applied to the skin, and they immediately irritate and inflame the skin. Histamine is probably responsible for the initial stinging sensation. However, nettle stings can have a therapeutic effect by acting as counter-irritants. Ironically, nettle juice can also be used as an antidote to painful nettle stings.

• Seeds
• Leaves
• Roots (rhizome) and underground parts (fresh and dried)

Flavonoids (in flowers) include glycosides of quercetins (isoquercetin, rutin), kaempferol, isohamnetin; amines (in stinging hairs) consist of small quantities of histamine, choline, acetylcholine, serotonin; chlorophylls; vitamins; triterpenes; sterols; carboxylic acids; minerals (high potassium and calcium salt content, silicic acid).

Commercial preparations are made from fresh or dried aerial parts of Urtica dioica, Urtica urens, hybrids gathered during the flowering season, or from dried root/rhizome. Tinctures and tea products are available, as are capsules made from dried or freeze-dried herb.

Traditional herbal actions: nutritive, alterative, circulatory stimulant, galactagogue, hypoglycemic, topical rubefacient (fresh leaves, only with caution), antihistaminic and antidote to stings (fresh juice)

Clinical applications: supportive treatments (internal and external) for rheumatic ailments; irrigation therapy for inflammatory diseases of lower urinary tract; prevention and treatment of kidney gravel. Diuretic effect if taken with sufficient fluid. Treatment of seasonal allergies, non-insulin-dependent diabetes. Root is used to treat micturition (urinary) disorders in benign prostatic hyperplasia (BPH) stages I and II, while the leaf is used for urinary tract infections, kidney and bladder stones, and rheumatism. It is also used as a topical compress or cream for arthritic joints, gout, sprains and strains, neuralgia, sciatica, tendonitis, burns, hemorrhoids, and insect bites. Fresh expressed juice is used for anemia and cardiac insufficiency with edema.

Open, observational, and placebo-controlled double-blind studies confirm that nettle root extract is efficacious for several conditions, including BPH. In vivo studies have shown that nettle herb has diuretic activity, presumably due to the presence of flavonoids and high potassium content. An aqueous root extract exhibited mild anti-inflammatory effects in a carrageenan-induced animal edema model.

In other animal studies, nettle had CNS-depressant, analgesic, hypoglycemic, and hyperglycemic effects. Urticin has been identified as the hypoglycemic principle responsible for lowering blood sugar levels in rabbits. Nettle herb extracts showed uterine activity in both pregnant and nonpregnant mice. The uteroactive effect was attributed to betaine and serotonin.

Stinging nettle root has a favorable effect on BPH by increasing urinary volume and maximum urinary flow while reducing residual urine. Although nettle root extract lessens the symptoms of enlarged prostate, it does not actually decrease the size of the prostate.

Prostate enlargement has been linked to elevated testosterone levels, specifically to increased activity of enzymes involved in testosterone production. An active principle in nettle is thought to either lower the amount of free testosterone or inhibit a crucial enzyme, such as aromase, required for testosterone production.

Nettle root extract interferes with testosterone synthesis by competitively displacing sex-hormone-binding globulin. However, the effective concentration needed for competitive displacement may be much greater than the concentration available in therapeutic doses.

The active constituent responsible for the anti-BPH effect has not been unequivocally determined, but it may consist of an agglutinin (a protein mixture called UDA) and several polysaccharides isolated from nettle root. Lectin induces interferon production by human lymphocytes and triggers nonspecific agglutination of erythrocytes. In an in vitro study, a component of UDA from nettle inhibited virus-induced cell damage caused by HIV-1, HIV-2, CMV, RSV, and influenza A.

In human clinical trials, nettle herb juice produced marked diuresis in patients with myocardial and chronic venous insufficiency, and showed hemostatic activity. And in a double-blind investigation, nettle herb was mildly efficacious in the treatment of allergic rhinitis.

• Dried herb: 2 to 4 g tid as infusion
• Fluid extract (1:1): 2 to 4 ml tid
• Tincture (1:5): 4 to 8 ml tid
• Fresh leaf infusion: 8 to 12 g fresh plant and ample liquid (at least 2 liters/day or equivalent)
• Root tincture/spiritus (1:10), for external use: 4 to 6 g/day or equivalent preparations (may be difficult to acquire in the U.S. except in blends)
• Topical compress, for external use: 4 to 6 g of herb in infusion

No major side effects. Skin exposure to Urtica dioica can cause a stinging sensation (contact urticaria). Nettle root tea taken orally can cause mild gastrointestinal complaints, gastric irritation, burning sensation of the skin, edema, and oliguria (decreased urine output in relation to fluid intake). Allergic reactions (edema, skin afflictions) to leaf preparations have been reported in rare cases.

Irrigation therapy should not be used if edema is present. The massive amounts of fluids required for irrigation therapy can cause fluid retention due to reduced cardiac or renal activity. Nettle has abortifacient activity, and it can alter the menstrual cycle. Pregnant women should not use nettle, and lactating women should avoid excessive use of this herb.

In an open randomized clinical trial of forty patients with acute arthritis, stewed stinging nettle leaves (50 g) enhanced the anti-inflammatory effect of diclofenac (50 mg) (Chrubasik et al. 1997). The combination of 50 mg of diclofenac plus stinging nettle was found to be as effective as 200 mg of diclofenac alone. Both groups showed evidence of improvement by about 70% over baseline values. Stinging nettle also enhanced the antirheumatic effectiveness of diclofenac as measured by a decrease in both C-reactive protein levels and clinical signs of acute arthritis.

The U.S. FDA classifies stinging nettle as a dietary supplement. It is listed on the General Sale List (GSL) in Britain. In Germany, nettle root is used as a therapy for urinary complaints during early stages of BPH. Stinging nettle is approved by the German Commission E.

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