Stinging Nettle: Effects on Joints, the Urinary Tract and Iron Deficiency

Maybe you got stung by it as a child. Maybe you drink it as tea today because someone told you it is good for the blood. Both are a good starting point for taking a closer look.

Behind these questions is a need I understand well. You want to do something natural for yourself. And you want to know whether it holds up.

To answer them, I look through several lenses: nutrient analyses, clinical trials, the assessment of the European Medicines Agency and KPNI. KPNI stands for Clinical Psychoneuroimmunology, the interplay of nerves, immune system, hormones and metabolism.

What is in stinging nettle? Nutrients, stinging hairs and silicon

A brief touch is enough. First it pricks, then it burns, then it itches for a while. Hardly any plant shows so clearly that it carries chemistry inside it.

Nature's smallest syringe

Every stinging hair is a tiny hypodermic needle. In 2018, a team led by Mustafa at the University of Bonn examined the stinging hairs of 43 plant species under the electron microscope. In the nettle family, the tips were reinforced with silica, that is, with silicon, while the shaft was mostly calcified.

When touched, the glassy tip breaks off, and the fine remainder penetrates the skin. Pressure then pushes the fluid in, much like a syringe. A review by the same Bonn group describes how acetylcholine, histamine and serotonin have been found again and again in the stinging hairs of the nettle family since the middle of the 20th century.

Your nervous system knows these messengers well. Histamine causes wheals and itching, and acetylcholine can irritate nerve endings. In the researchers' view, however, these substances do not fully explain the long-lasting burning.

A leafy vegetable with a nutrient profile

In many kitchens, nettle is eaten like spinach. Cooked, blanched or dried, it loses its sting.

Nettle leaves also contain plenty of polyphenols. In 2024, a group led by Opačić in Zagreb found caffeic acid compounds, ferulic acid and rutin, among others, in hydroponically grown nettles. This group of substances will come up again shortly when we get to iron.

And what about silicon?

Silicon is the element for which nettle is often praised in health guides. For skin, hair, nails and connective tissue, they say.

It is well documented that the stinging hairs carry silicon in their tips. As far as I know, no one has studied how much of it ends up in your tea and whether it plays a role for your body from there.

Four lenses on one plant

Through the KPNI lens, nettle touches all four major control systems of your body. Not equally strongly everywhere, and not equally well documented everywhere.

If you would like to eat nettle, young shoot tips in spring are a good choice. Briefly blanched, you can use them like spinach, for example in soups, stir-fries or pesto.

And now you know why nettle on your plate is something different from nettle in a tea bag.

Can nettle tea make up for an iron deficiency?

Tired despite sleep. Cold hands, brittle nails, more hair in your brush. And somewhere that sentence: drink nettle tea, it builds blood.

I like the idea that a wayside herb strengthens the blood. Folk medicine calls nettle blood-building. In my research, I did not find any human studies showing this for nettle tea.

The honest math

Let's do the math. A hundred grams of cooked leaves, a decent serving of vegetables, provide about 2 mg of iron. The European Food Safety Authority, EFSA, sets a reference value of 16 mg a day for women before menopause.

Then there is absorption. Iron from plants comes as so-called non-heme iron. According to a review by Hurrell and Egli of ETH Zurich, the body absorbs about 14 to 18 percent of dietary iron on a mixed diet. On a vegetarian diet, it is only 5 to 12 percent, both estimated for people without iron reserves.

Imagine your iron stores as a well. Nettle as a vegetable is a bucket that can add something. A cup of tea is more like a thimble.

And in tea?

When you make an infusion, only a small part of the minerals passes into the water. A Warsaw research group led by Długaszek measured the minerals in infusions of various herbal teas. On average, about 18 micrograms of iron per gram of dried herb passed into the infusion.

Nettle was among the more mineral-rich teas. Even so, the researchers concluded that herbal infusions cover only a small part of the daily requirement. For a cup made with two grams of herb, the average value would come to roughly 0.04 mg of iron.

The counterpart to these inhibitors is vitamin C. In 1989, a research group led by Hallberg in Gothenburg showed with labeled iron that added phytate, a substance found in grains and legumes, reduced iron absorption by up to 82 percent depending on the amount. Vitamin C with the meal was able to markedly weaken this inhibition.

What I look at instead when you are tired

If you are tired and thinking of iron, that is often a smart thought. It just needs to start with a measurement, not a tea regimen.

Iron deficiency begins long before anemia. First the stores empty, measured as ferritin. Only much later does hemoglobin drop. A 2021 review in The Lancet emphasizes that symptoms and limitations can occur even without anemia.

When there are symptoms, I consider a ferritin level above 100 µg/L a sensible target. That is my clinical position and not a general guideline recommendation. A systematic review of 29 guidelines did conclude, however, that a cutoff of 100 µg/L should be considered for diagnosing iron deficiency in most situations. It saw exceptions, for example, in young healthy women with heavy menstrual bleeding.

Seven of these guidelines even named a ferritin above 100 µg/L as a treatment target. Because ferritin rises with inflammation, I never look at ferritin alone. For me, transferrin saturation, hemoglobin and CRP are part of the picture.

When the stores are empty

Then the first question is not which tea, but why. The Lancet review recommends looking for the cause in every case of iron deficiency, for example celiac disease or sources of bleeding in the gastrointestinal tract. In women before menopause, menstrual bleeding often plays a major role.

According to this review, iron tablets are the first step in most cases. In the view of the authors from Melbourne, Heidelberg and Nijmegen, modern infusion products have fundamentally changed treatment. They make it possible to give the total amount needed quickly and safely.

You can find more about target values in Ferritin above 100 as a target, about deficiency despite unremarkable values in Functional iron deficiency and about diet in Improving iron absorption.

And now you know why, when you are tired, I ask about your ferritin first and only then about your tea.

What do studies show about stinging nettle for osteoarthritis and joint pain?

In the morning, your thumb is stiff. The jar is hard to open, and your knees make themselves felt on the stairs. And you are looking for something gentler than the next painkiller.

The sting as therapy

The idea is old. In folk medicine, people rub or beat fresh nettles onto painful joints. A British team from general practice wanted to know whether there is more to it than courage.

In 2013, a Cochrane review by Cameron and Chrubasik summarized studies on topically applied herbal remedies for osteoarthritis. For nettle leaf, it remained open whether it improves symptoms, because the evidence came from a single study of very low quality. The background section states that topical herbal remedies partly work as counterirritants.

You may know counterirritation from scratching. A strong new stimulus on the skin can draw your nervous system's attention away from the old pain. Whether this is the main mechanism with nettle, nobody knows for sure.

Nettle from the inside

Nettle has also been studied as a vegetable or extract, but rarely on its own.

In 2009, a French group led by Jacquet tested a dietary supplement with fish oil, vitamin E and nettle in 81 people with knee or hip osteoarthritis. After three months, the group taking the product needed considerably fewer painkillers. Experts led by Christensen commented, however, that the effect was unusually large and the risk of bias high.

The study had only been registered after it was completed, and the fishy taste could have revealed who received the real product. Because the product contained several active ingredients, the contribution of nettle cannot be singled out anyway.

What might happen in the joint

Through the KPNI lens, a painful joint is also a site of immune defense. Cartilage cells and immune cells there send out messengers such as interleukin-1 and TNF-alpha. Many of these signals run through a cellular master switch called NF-kappaB.

A 2007 review from Freiburg summed it up: clinical and experimental studies point to anti-inflammatory properties of nettle herb. Unequivocal clinical proof is lacking.

If you want to try the nettle sting, then not on irritated or injured skin and not if you have known skin allergies. I describe what exercise can do for knee osteoarthritis in Exercise for osteoarthritis. You can find two more plants with joint studies in Turmeric for osteoarthritis and Frankincense for joints and gut.

And now you know why I see nettle more as a supporting act than as the lead role when it comes to joint pain.

Nettle root and the prostate: what does the evidence show?

Three in the morning, up for the second time. The stream is weaker than it used to be, and the feeling of not being quite empty remains. Many men over 50 know this and do not like to talk about it.

Important up front: for the prostate, it is about the root, not the leaf. They are two different herbal substances, each with its own European monograph.

Other studies tested combinations with saw palmetto fruit. In a multicenter study from Moscow with 257 men, the IPSS fell by six points after 24 weeks with the combination, and by four with placebo. In an analysis from Dortmund, the same combination showed an effect similar to the drug finasteride, with better tolerability.

Here, too: with combinations, the contribution of nettle cannot be cleanly separated.

The big study with a question mark

An Iranian study from 2005 with 620 men is often cited. With nettle, 81 percent reported fewer symptoms, with placebo 16 percent. The prostate even became somewhat smaller on ultrasound.

I give this study cautious weight. It has a single author, and journals have since published retraction notices for several other papers by this author, for example the journal Neuropsychopharmacology in 2023. To my knowledge, the nettle study itself has not been retracted.

This says nothing final about this one paper. But it is a reason not to make it the basis for big hopes. The author himself wrote that further studies were needed before efficacy could be assumed.

How the root might work

Through the hormonal lens, it gets interesting. SHBG is a transport protein, a kind of taxi for sex hormones in the blood. It can also dock onto cells of the prostate.

The Committee on Herbal Medicinal Products of the European Medicines Agency revised its monograph on nettle root in January 2025. It lists the root as a traditional herbal medicinal product for urinary complaints caused by a benign enlargement of the prostate. The prerequisite is that serious conditions have been ruled out by a doctor. The committee does not classify it as a well-established medicinal use.

And now you know why, with the prostate, the assessment comes first and the root second.

Flushing, shedding water, detoxing: what can nettle tea do for your kidneys and urinary tract?

Spring, the scale shows two kilos more, and your ankles are swollen in the evening. Everywhere you read about cleansing, detox and spring cleanses. And nettle tea is almost always part of it.

I understand the wish for a fresh start. The need behind it is legitimate: to feel lighter, to clear things out, to do something for yourself.

What flushing means

The monograph on nettle leaves is remarkably precise here. It speaks of more urine to flush the urinary tract, as a supportive measure in mild complaints. In doing so, it relies exclusively on long-standing use, not on clinical trials.

Why detox cleanses overpromise

In 2015, an Australian review by Klein and Kiat examined the evidence for detox diets. Their conclusion: there is hardly any clinical evidence, and the existing studies have methodological weaknesses and small numbers of participants. The authors found no randomized trials of commercial detox programs in humans.

More urine does not mean fewer toxins. Your liver and your kidneys work every day, with no cleanse at all. And what the scale shows after a week of tea may be mostly water.

Swollen legs are also a signal, not a tea problem. They can come from the heart, the kidneys, the veins or from medication. The monograph explicitly lists conditions in which fluid intake should be reduced, such as severe heart or kidney disease, as a contraindication.

How much drinking makes sense for your kidneys is covered in Kidneys, water and detox. You can find a detailed assessment of juice cleanses and detox teas in A critical look at detox cleanses. And if your main concern is weight, it is worth taking a look at Why am I not losing weight?

And now you know why I take nettle tea seriously as a way to flush the urinary tract, but not as a detox cleanse.

Can stinging nettle lower blood sugar? And what about hay fever?

These two questions often come up in health guides. The data here are thinner, but not empty.

In 2022, a second meta-analysis led by Tabrizi with 13 clinical trials additionally found an HbA1c just under one percentage point lower. CRP was also about 1 mg/dL lower and systolic blood pressure about 5 mmHg lower. An Iranian study led by Kianbakht with 92 people requiring insulin saw lower fasting values, lower values after meals and a lower HbA1c after three months of leaf extract.

And for hay fever?

In 2009, lab experiments by a US company, led by Roschek, showed that a nettle extract could block the histamine H1 receptor and slow the release of inflammatory substances from mast cells. That is a plausible mechanism. Whether it holds up in humans at usual amounts is an open question.

You can find out what cinnamon can and cannot do for blood sugar in Cinnamon and blood sugar.

And now you know why nettle plays a supporting role in blood sugar, one you should still know about.

How safe is stinging nettle? Side effects and interactions

The good news first: nettle is considered well tolerated. The European monographs list mild gastrointestinal complaints and skin reactions, and for the root also heartburn, a feeling of fullness and allergic reactions. No interactions with medications are reported there.

But not reported does not mean ruled out. Interactions have hardly been studied systematically. From the known effects, however, some precautions can be derived.

Gathering it yourself?

Gathering nettles can be a lovely spring ritual. The Zagreb research group led by Opačić points out, however, that the quality of wild-harvested plants is difficult to control. So only gather where you know the location well, and avoid busy roads.

For how long?

The monograph limits the traditional use of the leaves to four weeks for joint complaints and to two to four weeks for flushing. If complaints persist, it advises seeking medical advice. For the root, longer use is considered possible.

And now you know why even a gentle herb deserves a place on your medication list.

Stinging nettle at a glance: what is backed by evidence, and what is not?

Here I separate what human studies show, what is mechanistically plausible and what is based mainly on tradition.

Three levers if you want to use stinging nettle wisely

You do not have to give up nettle. You can use it in a more targeted way. These three steps are not a therapy but an order of steps that I consider sensible.

If you find yourself nodding at one of these points, that is no reason to worry. It is a good reason to talk to your doctor before your next tea regimen. You can find more about plant-based eating and full iron stores in Iron deficiency on a vegan or vegetarian diet.

And now you know why nettle can do the most for you when you know what you expect from it.

Frequently asked questions about stinging nettle

Where this topic also comes into play

Iron, joints and detoxification are cross-cutting topics. These articles approach them from other directions.