Eucommia Bark

What is Eucommia Bark?

Eucommia bark is the dried stem bark of Eucommia ulmoides Oliv., the only living species in the family Eucommiaceae, and a snapped piece of it pulls apart on silvery, elastic threads of rubber. The threads are trans-1,4-polyisoprene, the gutta-percha type of natural rubber, chemically the geometric isomer of the cis-polyisoprene tapped from the tropical Hevea tree.

The tree is a deciduous hardwood of central China. In Chinese medicine the bark is du zhong, an "upper grade" drug first recorded in the Shen Nong Ben Cao Jing, and the Pharmacopoeia of the People's Republic of China 2020 credits it with tonifying the liver and kidney, strengthening "muscles, bones, and placenta," and treating waist and knee pain, dizziness, bleeding in pregnancy and "restless fetal movement," per the summary in Tang and colleagues' 2025 trial report. The same pharmacopoeia separately lists the leaf, du zhong ye, as its own drug with its own marker compound. Bark and leaf come from one tree and are sold under one English name, and that is where this issue's problem starts.

Common Names

• Eucommia, eucommia bark, hardy rubber tree, gutta-percha tree (the last also used for unrelated Palaquium species, a source of confusion)

• Du zhong (Chinese, bark); du zhong ye (Chinese, leaf); yan du zhong (salt-processed bark)

• Tochu (Japanese, bark); tochu-cha (Japanese leaf tea, the leaf not the bark)

• Eucommiae Cortex (pharmacopeial Latin, bark); Eucommiae Folium (leaf)

Primary Active Compounds

• Lignans, led by (+)-pinoresinol di-O-beta-D-glucopyranoside (pinoresinol diglucoside, PDG), the bark's pharmacopeial marker, plus related pinoresinol and syringaresinol glycosides

• Iridoid glycosides: aucubin, geniposidic acid, geniposide, asperuloside and the bark-specific eucommiol

• Phenylpropanoids, chiefly chlorogenic acid, the leaf's pharmacopeial marker

• Flavonoids including quercetin and hyperoside

• Eucommia gum (trans-1,4-polyisoprene), with no established pharmacology but real value as an identity marker

Key Note

Li and colleagues at Nihon University (Biological and Pharmaceutical Bulletin 2000;23:54) reported that geniposidic acid and aucubin are present at high concentration in fresh bark, but that "during the drying process and storage, most of them were destroyed by enzymes in the cortex and very little remained" in the finished drug. Geniposidic acid is the compound on which Japanese blood pressure labels for eucommia leaf tea are built. The bark's traditional processing, piling freshly peeled bark for 5 to 7 days until the inner surface turns purplish brown (HKCMMS), is part of the drying process Li's group blamed.

One tree, two drugs, two chemistries, and a blood pressure literature that does not keep them apart.

Primary Functions & Benefits

Eucommia bark's documented functions in people come down to one modest, inconsistent blood pressure signal from a handful of small trials, measured with products that are not what most US bottles contain. Everything about tendons and bones is animal or cell work.

Blood pressure: the bark trials, one by one

Greenway and colleagues at the Pennington Biomedical Research Center, Louisiana State University (Alternative Medicine Review 2011;16:338) ran three studies on an aqueous bark extract standardized to 8 percent pinoresinol diglucoside. In Study 1, 24 adults with blood pressure between 120 to 160 systolic and 80 to 100 diastolic were randomized to 500 mg three times daily (1.5 g a day) for 8 weeks, with 24-hour ambulatory monitoring at baseline and the end; there was "no toxicity or any difference in BP between the two groups." In Study 3, 30 adults in the same pressure range were randomized to 1 g three times daily (3 g a day) for 2 weeks, and the abstract reports an average reduction of 7.5/3.9 mmHg (P < 0.008). The abstract does not name the comparator; Drugs.com's monograph, summarizing the full paper, reports the result as P < 0.008 against placebo in 29 participants. The lower, longer dose did nothing; the higher, shorter one moved pressure for two weeks.

Xu and colleagues at Xiyuan Hospital, China Academy of Chinese Medical Sciences (Frontiers in Pharmacology 2023;13:1014410) ran the only multicenter, double-blind, placebo-controlled bark trial the author found. Sixty adults with grade 1 hypertension (140 to 159/90 to 99 mmHg) at low to moderate risk were randomized at three hospitals; after a 1-week placebo run-in, 58 (29 per arm) entered a 4-week treatment period with Quanduzhong capsules, three capsules twice daily. The two primary endpoints split. Mean 24-hour ambulatory pressure fell 2.52/1.17 mmHg on the capsule and 1.93/0.41 mmHg on placebo, a difference that was not significant (P = .58 systolic, .34 diastolic). Office pressure fell 7.62/4.66 mmHg on the capsule against 3.55/0.38 mmHg on placebo in the full analysis set (P = .03 systolic, .01 diastolic). In the per-protocol set of 51 (29 capsule, 22 placebo), the systolic office difference lost significance (P = .13) and only the diastolic held (P = .03). The manufacturer, Jiangxi Puzheng Pharmaceutical, supplied the capsules and matching placebo, and four of the coauthors list it as their affiliation. Xu's paper also cites an earlier trial by Jiang and colleagues in which Quanduzhong capsules lowered office systolic and diastolic pressure against sham capsules over 12 weeks, and Tang's 2025 report, citing Jiang and colleagues (2022) as its authors' own earlier 12-week grade 1 trial, gives pressure control rates of 55.17 versus 24.14 percent against control. Neither earlier report was reviewed in full for this issue.

Tang and colleagues (Frontiers in Pharmacology 2025;16:1659073) then added the same capsules, three twice daily for 12 weeks, to the existing medication of 136 adults with essential hypertension and a non-dipping nighttime pattern. It was open-label with no placebo. In the full analysis set of 126 and the per-protocol set of 103, there was no significant difference between groups in the primary endpoints (dipper recovery rate, pressure standard deviation, coefficient of variation) or in clinic, home or ambulatory mean pressure. Among patients already taking a calcium channel blocker, the control group's ambulatory diastolic pressure fell further than the eucommia group's. The positive finding in the abstract comes from a subgroup of 39 people not on calcium channel blockers, on one variability measure (24-hour diastolic standard deviation, P = 0.04).

Blood pressure: the leaf trials

The NIBIOHN database entry for eucommia lists three Japanese randomized, double-blind, placebo-controlled 12-week trials: 85 adults (41 on active) drinking 50 mL a day of a leaf extract beverage with at least 1.0 g of leaf glycosides, with systolic and diastolic pressure lowered (Health Sci. 2004;20:166, as cited by NIBIOHN); 87 adults (44 on active) drinking 350 mL a day with at least 80 mg of geniposidic acid, with systolic lowered and diastolic unchanged (Health Sci. 2005;21:198); and 42 men and postmenopausal women (19 on active) with high-normal pressure drinking 350 mL with 85 mg of geniposidic acid, with systolic lowered and diastolic and flow-mediated dilation unchanged (Hosoo and colleagues, Japanese Pharmacology and Therapeutics 2015;43:195). Nishibe's 2023 review describes the Hosoo trial differently, as 46 adults (28 men, 18 women), and reports flow-mediated dilation improving by 1.29 percentage points at 8 weeks against minus 0.01 on placebo; it also reports diastolic lowering from week 8 in an 80 mg geniposidic acid trial by Tsukamoto and colleagues. None of these used bark.

Tendon, ligament and connective tissue

This is the traditional indication behind the phrase "strengthens sinew and bone," and the author found no human trial of it. The evidence is in rodents and dishes, and it splits by plant part. Li and colleagues (Biological and Pharmaceutical Bulletin 1998;21:1306) reported that leaf extracts increased collagen synthesis in a "false aged" rat model and traced the effect to geniposidic acid and aucubin. When the same group tested dried bark (2000), the active compound was a different iridoid, eucommiol, and the authors noted that the leaf's two actives had largely been destroyed in the dried bark. Zhang and colleagues at Changchun University of Chinese Medicine (Pharmaceuticals 2026;19:194) identified aucubin as the major constituent of an active bark fraction and reported better structural and functional recovery, a higher type I to type III collagen ratio and lower MMP-3 and MMP-13 in a collagenase-induced Achilles tendinopathy model in male Sprague Dawley rats. No study the author found has measured a tendon, ligament or joint outcome in a person taking eucommia alone.

Bone, briefly

A 2026 scoping review (Wang and colleagues, Frontiers in Pharmacology 16:1673870) found 90 eligible studies, almost all cell and rodent work, and tabulated 10 clinical studies of eucommia preparations in osteoporosis. None listed a placebo arm. Nine paired eucommia with or against another treatment (alendronate, alfacalcidol, calcitonin, calcium and vitamin D, vertebroplasty or another herbal product), the tenth was a before-and-after metabolomics study with healthy volunteers as the comparison, and the reviewers rated them "low-to-moderate methodological quality and a high risk of bias," with no trial describing allocation concealment.

Forms & Standardization

Four very different things are sold as "eucommia," and only one of them is what the pharmacopeias call Eucommiae Cortex.

Crude dried bark, cut or powdered

The pharmacopeial article. The HKCMMS monograph defines it as stem bark collected April to June, the coarse outer layer scraped off, piled 5 to 7 days until the inner surface turns purplish brown, then sun-dried. The assay is HPLC for pinoresinol diglucoside, not less than 0.10 percent on the dried drug, with limits of 1.0 percent foreign matter, 8.5 percent total ash, 6.0 percent acid-insoluble ash and 12.0 percent water, and minimum extractives of 10.0 percent (hot water) and 13.0 percent (hot ethanol). Retail bark capsules are this material ground. Swanson's Full Spectrum Eucommia Bark is a representative US example: 400 mg of Eucommia ulmoides bark per capsule, one capsule a day, no extract ratio, no marker compound and no statement of whether the bark was raw or salt-processed.

Salt-processed bark (yan du zhong)

Bark processed with salt and heat ("salt-fired" in one research group's translation). The Chinese Pharmacopoeia 2015 lists crude and salt-processed bark as separate clinical forms, and specifies the salt form for patent formulas including Yougui Wan, Tianma Wan and Qing'e Wan (Guo and colleagues, Frontiers in Pharmacology 2020). Zhu and colleagues (Chinese Traditional and Herbal Drugs 2024;55:3291) measured what the process does: the strength of the rubber threads falls "extremely significantly," hyperoside falls, and geniposidic acid, chlorogenic acid and geniposide rise. Guo's group argued that the 0.10 percent pinoresinol diglucoside minimum cannot tell crude from salt-processed bark. A label that says only "eucommia bark" does not say which one it is.

Standardized bark extracts

The Greenway trials used an aqueous bark extract at 8 percent pinoresinol diglucoside, about 80 times the crude drug's 0.10 percent minimum, so 1.5 g of that extract delivered roughly 120 mg of the lignan and 3 g about 240 mg. The paper's abstract does not name a commercial product or extract ratio.

The Chinese drug capsule

Quanduzhong capsules, made by Jiangxi Puzheng Pharmaceutical and approved by China's drug regulator, are a pharmaceutical, not a supplement. Each capsule represents 2.5 g of crude bark, and the trial dose of six a day represents 15 g of bark.

Leaf products

Leaf tea (tochu-cha) and leaf extracts are standardized, when they are standardized at all, to geniposidic acid (Japanese functional foods) or chlorogenic acid (Chinese Pharmacopoeia leaf monograph, minimum 0.080 percent). A 2023 analysis of 20 batches of Chinese leaf (Feng and colleagues, Chinese Traditional and Herbal Drugs 54:2931) found chlorogenic acid at 2.634 to 6.183 percent, 33 to 77 times that minimum, geniposidic acid at 0.078 to 0.977 percent and aucubin at 0.053 to 4.563 percent. The same paper found pinoresinol diglucoside in leaf at 0.065 to 0.215 percent, and 6 of the 20 leaf batches would have passed the bark's 0.10 percent minimum. The bark's marker compound cannot prove a capsule contains bark.

Food Sources

The bark is not eaten as a food. The edible part of the tree is the leaf, and Japan has built two kinds of health claim on it. NIBIOHN records that Foods for Specified Health Uses with eucommia leaf glycosides as the functional ingredient have been approved with the claim "suitable for people with somewhat high blood pressure"; the author could not confirm which company holds those approvals. The leaf product described below is in Japan's newer, notification-based Food with Function Claims category instead.

Leaf tea, the food form with the human data

Kobayashi Pharmaceutical's Kekkan Tochu-cha ("blood vessel" tochu tea) is a current Food with Function Claims in Japan, 100 percent leaf, 2.5 g per bag. The label declares 85 mg of leaf-derived geniposidic acid per daily serving of two bags, measured after the recommended preparation of simmering both bags in about 1 L of water for about 10 minutes, and says the leaves are hand-picked from May to August, when geniposidic acid is highest. Its claim is that leaf geniposidic acid "has been reported" to lower blood pressure in people whose pressure is on the high side and to help maintain vascular flexibility that declines with age. That 85 mg matches the dose in the 2015 Hosoo trial, which delivered it in 350 mL of a prepared beverage. A home brew in 1 L reaches the same milligrams only if the whole liter is drunk.

What else rides along in the leaf

Nishibe's group analyzed leaf extract from Japanese and Chinese leaves standardized to 85 mg geniposidic acid and found 48.6 to 75.7 mg of chlorogenic acid and 14.8 to 21.6 mg of asperuloside in 1.20 to 1.33 g of extract. They judged that chlorogenic acid quantity too small to explain any blood pressure effect, citing 185 mg a day as the lowest effective human dose from coffee bean studies.

Is diet sufficient?

There is no dietary requirement to meet. The Japanese blood pressure evidence is on a leaf beverage; a bark capsule is a different product.

Who Should Take Eucommia Bark

No group has been shown to benefit from a eucommia bark supplement as sold in the United States. The populations below are the ones that have been studied, with the products they were studied on.

Adults with high-normal pressure or grade 1 hypertension, untreated

Greenway's subjects (120 to 160 over 80 to 100 mmHg) and Xu's (grade 1, low to moderate risk, 140 to 159 over 90 to 99) are the only bark-trial populations not already on medication, and their results are mixed (see Primary Functions). Anyone in this group has a number that can be measured at home, and a supplement should not replace measuring it.

People inside a Chinese medicine practice

Du zhong is prescribed in decoctions and patent formulas, raw or salt-processed, by practitioners who choose the form for the indication. A patient in that system has a prescriber, a form and a dose; a shelf buyer has none of the three.

Who gains nothing

Anyone buying it for a tendon, ligament or joint injury. The author found no human study of eucommia alone for any of those, and the rat data are on isolated aucubin or eucommiol rather than on a capsule of bark powder.

Who Should AVOID or Use Caution

Contraindications

• People taking blood pressure medication, unless the prescriber knows and is monitoring. In Tang's 2025 add-on trial, three participants had hypotensive reactions after starting the capsules on top of their usual drugs; the symptoms resolved when the capsules were stopped and all three withdrew.

• Pregnancy and breastfeeding. The Chinese Pharmacopoeia's indications for the bark include bleeding in pregnancy and "restless fetal movement," a traditional use with no modern safety data behind it. Both Quanduzhong trials excluded pregnant and lactating women, and the Health Concerns Backbone formula, which contains eucommia bark, states it "is not intended for use by pregnant women."

• Children. The author found no pediatric data for any form.

• Known kidney disease. A 13-week rat study (Luo and colleagues, Regulatory Toxicology and Pharmacology 2020;118:104811) found dose-dependent kidney injury on repeated dosing; see Toxicity.

Use Caution

• Latex allergy or sensitivity. Australia's Therapeutic Goods Administration advises avoiding Eucommia ulmoides medicines, citing the plant's latex and one allergic reaction report (see Potential Negatives).

• Low baseline pressure, orthostatic dizziness, or a history of fainting. A product that lowers pressure in some people can unmask this.

• Beta-blockers (metoprolol, atenolol, propranolol, bisoprolol). Greenway's group reported that the bark extract at 0.5 percent w/v cut isoproterenol-stimulated lipolysis in human fat cells from 2.67 to 1.4 times buffer control (P < 0.001) and concluded it "has beta-adrenergic blocking activity." Stacking two beta-blocking influences is untested.

• Diabetes medication. Leaf extracts have glucose-lowering animal data; glycemic effects are covered in the Curry Leaf issue and not repeated here.

• Anticoagulants and antiplatelet drugs. Monographs list a theoretical additive effect; no eucommia-specific bleeding case was found, and that topic belongs to the Danshen issue.

• Scheduled surgery, because of the pressure effect. Stop at least two weeks before.

Critical Safety Point

The one hazard the author found documented in a human trial is the obvious one: added to existing antihypertensive drugs, eucommia bark capsules dropped pressure far enough in 3 of 68 people randomized to them that they left the trial. A bottle sold for "healthy blood pressure" is most likely to be bought by exactly the people already on those drugs.

Recommended Dosages

There is no dose of eucommia bark that any regulator or clinical guideline recommends to US supplement buyers, and the author found no human trial of the plain bark powder in most capsules. The amounts used in research belong to specific products and are reported, scoped, in Special Considerations, not here.

Bark powder capsules

Retail labels set their own figure; Swanson's, for example, is one 400 mg capsule a day. The author found no human outcome measured at that amount or anything close to it, so the number on the label is a convention, not a dose.

Standardized bark extracts

Only an extract that states its pinoresinol diglucoside percentage can be compared with the Greenway extract, the only one the author found tested in a published trial.

Leaf tea (a different product)

Japanese functional leaf teas print their own directions, two bags (85 mg geniposidic acid) a day for the Kobayashi product. That is a direction for a leaf beverage under Japanese food law, not a bark dose.

Duration

The longest bark blood pressure trial ran 12 weeks (open-label, add-on); the longest placebo-controlled bark exposure reviewed in full here is 8 weeks (Greenway Study 1, the null one), though Xu's paper cites a 12-week sham-controlled Quanduzhong trial by Jiang and colleagues. The leaf trials ran 12 weeks. Some Chinese osteoporosis studies of eucommia preparations ran 6 months, without placebo arms and alongside other treatments. The author found no placebo-controlled safety data past 12 weeks.

Timing & Administration

The author found no human pharmacokinetic study of eucommia bark. Pinoresinol diglucoside, the bark's marker, had an oral bioavailability of only 2.5 percent in rats (Song and colleagues, Pakistan Journal of Pharmaceutical Sciences 2015;28:2083), so little of it reaches the bloodstream intact. What schedules exist come from trial protocols. Greenway dosed three times daily. The Quanduzhong trials dosed twice daily, Tang specifying 8:00 to 10:00 and 20:00 to 22:00. The Japanese leaf trials used one beverage a day.

One practical point follows from the safety record rather than from pharmacokinetics. Anyone on blood pressure medication who starts eucommia with a prescriber's knowledge should check pressure at home in the first weeks, since the hypotensive reactions in Tang's trial appeared after starting the capsules.

Timeline of Effects

When an effect has been seen

• Hosoo, leaf beverage: significant pressure lowering from week 4, per Nishibe's summary.

• Tsukamoto and colleagues, leaf beverage: systolic differences at weeks 6, 8, 10 and 12 and diastolic at weeks 8, 10 and 12, per Nishibe's summary. (NIBIOHN's summary of the 80 mg geniposidic acid trial records systolic change only, and the two sources may be describing different publications.)

• Greenway Study 3, standardized bark extract (regimen in Special Considerations): a 7.5/3.9 mmHg fall at 2 weeks.

• Xu, Quanduzhong drug capsule under trial supervision: office pressure change at 4 weeks, with no 24-hour ambulatory change.

When an effect was looked for and not found

• Greenway Study 1, the lower extract regimen: nothing at 8 weeks.

• Tang, Quanduzhong capsule added to medication: nothing between groups at 12 weeks in the full or per-protocol sets.

A fair trial

Given that the leaf studies needed 4 to 8 weeks to separate from placebo, a reader who has chosen to try a product, with a clinician's knowledge, would need home cuff readings over 8 to 12 weeks, taken at the same time of day, to know anything. A single office reading is not evidence; Xu's own trial showed office and 24-hour readings disagreeing in the same patients. If home pressure has not moved by 12 weeks, nothing in the published record suggests it will.

Tendons and bones

No human timeline has been published that the author could find. The rat tendon model ran weeks; whether a person would see anything at any time point is unknown.

Benefits of Taking Eucommia Bark

Documented in humans, bark

A modest and inconsistent blood pressure effect, present in two of the four bark studies examined in full in Primary Functions and absent in the other two; a cited 12-week sham-controlled Quanduzhong trial also reported an office pressure fall. Xu's trial also reported that homocysteine fell by 6.23 µmol/L in the three capsule-arm patients who started with abnormal levels; three people is an anecdote, and the authors said so.

Documented in humans, leaf (not bark)

Systolic pressure reductions in three Japanese 12-week placebo-controlled trials of leaf beverages. In China, Nishibe's review reports a trial in 27 adults with abdominal obesity (15 active, 12 placebo) given 1,500 mg of Kobayashi leaf extract in capsules for 8 weeks, with visceral fat area falling from 270.1 to 214.7 cm² and weight from 97.2 to 95.9 kg. The same review says the authors' own trial in Japanese subjects "did not observe significant anti-obesity effects other than body fat reduction."

Documented in animals

• Gu and colleagues at Central South University (Journal of Ethnopharmacology 2010;133:6) gave spontaneously hypertensive rats 300 mg/kg a day of lignans extracted from the bark for 16 weeks; mean arterial pressure fell, as it did on captopril, and hypertensive remodeling of the aorta and mesenteric artery was reversed.

• Lang and colleagues at Louisiana State University (American Journal of Chinese Medicine 2005;33:215) gave an E. ulmoides extract to spontaneously hypertensive rats for 22 days. From day 8, the 600 and 1,200 mg/kg doses lowered systolic pressure in males but not females, and 600 mg/kg was the minimum effective dose.

Marketed, undocumented

"Liver and kidney support" (the Swanson label's headline), "yang tonic," and joint, tendon and back support. The first two are translations of Chinese medicine concepts with no measurable endpoint attached. The last has rat data only.

Potential Negatives & Side Effects

From the human trials

• Xu 2023, 4 weeks, safety set of 59: adverse events in 12 of 30 on capsules (40 percent) and 10 of 29 on placebo (34.48 percent); events judged drug-related in 8 (26.67 percent) and 6 (20.69 percent). The differences were not significant (P = .66 and .59) and all events were mild.

• Tang 2025, 12 weeks: 13 adverse events, including the 3 hypotensive reactions on capsules that led to withdrawal, and one fatal heart attack in a control patient who had not taken the capsules.

• Greenway 2011: the abstract reports the extract "well-tolerated" with "no toxicity." Drugs.com's monograph, summarizing the full paper, lists headache, dizziness, edema and onset of a cold described as "moderately severe," and small rises in serum glucose (3 ± 2 mg/dL) and creatinine (0.02 ± 0.01 mg/dL); the author has not seen the full text to confirm these figures.

From the product

The Swanson bark capsule listing carries a California Proposition 65 warning for "cancer and reproductive harm." The warning does not name the chemical, and a Proposition 65 warning can be triggered by a trace contaminant such as lead rather than by the ingredient itself. A buyer can ask the company which chemical and at what level.

Allergy

Australia's Therapeutic Goods Administration issued a safety alert, reported in the Australian pharmacy press in January 2021, on listed medicines containing Eucommia ulmoides, stating that the plant "contains naturally occurring latex," noting one report of an allergic reaction to a multi-ingredient product containing it, and advising people with a latex allergy or sensitivity to avoid these medicines. The author found no published case report of allergy to eucommia bark or leaf in PubMed.

Deficiency Symptoms

What eucommia bark addresses

No deficiency. Nothing in the bark (pinoresinol diglucoside, aucubin, eucommiol, rubber) is required by the human body or has a blood reference range. "Kidney deficiency," the Chinese medicine pattern du zhong is prescribed for, describes a cluster of symptoms (lower back and knee soreness, tinnitus, aversion to cold) in that system's terms. It is not a shortage of any substance, and no laboratory test diagnoses it.

Bottom line

Back and knee pain, dizziness and high pressure each have a diagnosis, and none of them is a eucommia shortfall.

Toxicity Symptoms

At high intake

The most complete toxicology study the author found is Luo and colleagues at the Institute of Medicinal Plant Development, Chinese Academy of Medical Sciences (Regulatory Toxicology and Pharmacology 2020). Doses are expressed as raw-plant equivalents, and the abstract does not say which plant part was extracted. The extract was not genotoxic in the Ames test (0.0352 to 22 mg per plate), the bone marrow micronucleus assay (22 to 88 g/kg) or a chromosomal aberration assay (2 to 20 mg/mL), and the maximum tolerated single dose was not less than 168 g/kg, which the authors put at 1,260 times the adult clinical dose. Repeated dosing was different. Over 13 weeks, nephrotoxicity indices rose dose-dependently, with pathological changes in kidney tissue. Five weeks after dosing stopped, the changes had eased at 11.2 g/kg and persisted at 56 g/kg. The authors' conclusion: "long-term and high-dose administration can lead to partly reversible nephrotoxicity." Separately, Li and colleagues noted toxicity in rats when isolated geniposide, a bark iridoid, was given above 50 mg/kg a day.

Lang's 2005 rat work found no toxicity by clinical signs, histopathology or serum chemistry at 200 to 1,200 mg/kg of extract daily for 28 days. Twenty-eight days is too short to show what Luo found at 13 weeks.

Signs to reduce or stop

• Lightheadedness on standing, fainting, or home readings below the target a clinician has set

• New ankle swelling

• A rise in serum creatinine or a fall in eGFR on routine bloodwork

• Unusual fatigue or slow pulse in someone also taking a beta-blocker

• Any use at all in pregnancy

General note

The acute margin is wide. The signal that matters is the 13-week kidney finding, because people with high blood pressure are also the people most likely to have strained kidneys.

How Eucommia Bark Works

The bark's blood pressure chemistry has three candidate routes, each demonstrated in tissue or rodents, none yet traced to a plasma concentration in a person.

Endothelial nitric oxide and potassium channels

Kwan and colleagues at McMaster University published two papers in 2003. In isolated rat aorta and dog carotid artery precontracted with 1 µM phenylephrine (Vascular Pharmacology 40:229), aqueous extracts of both bark and leaf caused concentration-dependent relaxation that disappeared when the endothelium was removed and was abolished or largely blocked by the nitric oxide synthase inhibitor L-NAME and by methylene blue. Atropine did not block the bark's effect, so it is not acting through muscarinic receptors; tetraethylammonium (3 to 5 mM) and 4-aminopyridine (3 mM) did, implicating potassium channels. A methanol extract of leaf had no effect at all, an early hint that solvent decides what a "eucommia extract" can do. In smaller rat mesenteric arteries (Naunyn-Schmiedeberg's Archives of Pharmacology 369:206), L-NAME only partly blocked the bark extract's relaxation, and the remainder was attributed to endothelium-derived hyperpolarizing factor, a larger share in the smaller, more distal vessels that set peripheral resistance.

Beta-adrenergic blockade

Greenway's group tested whether the bark extract behaves like a beta-blocker by measuring isoproterenol-driven fat breakdown in human fat cells, and it did, cutting stimulated lipolysis by roughly half at 0.5 percent w/v. Nishibe's 2023 review reads the trial's 24-hour heart rate data as consistent with beta-blockade. A beta-blocker lowers pressure partly by slowing the heart and reducing renin release; whether an oral bark dose reaches cardiac receptors at a meaningful concentration has not been measured.

Pinoresinol diglucoside and cyclic AMP

Charles J. Sih isolated pinoresinol glycosides from an acetone and ethanol extract of Tu-Chung bark and patented them as antihypertensives for the Wisconsin Alumni Research Foundation (US Patent 4,103,006), with activity measured in spontaneously hypertensive rats. Nishibe's review credits pinoresinol diglucoside with strong inhibition of cyclic AMP phosphodiesterase. The weak link is absorption: 2.5 percent oral bioavailability in rats (Song, 2015). A compound that barely reaches the circulation intact can still act through gut metabolites, but no published study the author found has identified which.

Why the leaf's mechanism does not transfer

In spontaneously hypertensive rats, a single oral dose of 100 mg/kg geniposidic acid cut systolic pressure from 203.2 to 153.0 mmHg at 6 hours, against 183.6 mmHg in controls, and raised plasma atrial natriuretic peptide to 69.4 pM against 46.2 pM, which Nishibe's group traced to activation of the GLP-1 receptor on the heart's atria. In humans that route did not appear. The same group writes that geniposidic acid "promotes natriuresis, but promotes neither ANP secretion nor antihypertensive effects in humans," matching what Skov and colleagues reported for the GLP-1 drug liraglutide, a sentence that sits awkwardly beside the leaf beverage trials their collaborators ran. They resolve it by proposing that the leaf's human effect runs through anti-inflammatory and endothelial pathways, and that the ANP route might need pinoresinol diglucoside alongside geniposidic acid. Read with Li's finding that drying strips most geniposidic acid and aucubin from the bark, the conclusion is that leaf and bark lower pressure, to the extent they do, by different chemistry, and a result on one is not evidence for the other.

Connective tissue chemistry

In hydrogen peroxide-injured tenocytes, Zhang's group found aucubin reduced apoptosis, reactive oxygen species, malondialdehyde, IL-1 beta and TNF-alpha, an effect blocked by an estrogen receptor beta antagonist. Aucubin is one of the iridoids Li reported lost in drying, so how much reaches a capsule of dried bark powder is unknown.

What is not known

The plasma concentration of any bark compound after an oral dose in a human. Without it, none of the above can be scaled from a dish to a capsule.

Synergistic Supplements

The author found no human trial testing any combination against eucommia bark alone. The pairings below are the ones a buyer will meet.

• Dipsacus root (xu duan) and achyranthes root (niu xi). The classic Chinese partners for "sinew and bone." Du-Zhong-Wan is bark and dipsacus 1:1; Li and colleagues (Pharmaceutical Biology 2016;54:1857) tested its water extract in 60 ovariectomized rats over 12 weeks, not in people.

• Other "blood pressure" botanicals. Hibiscus, olive leaf and hawthorn have their own trials in their own issues. Stacking any of them on eucommia stacks unmeasured pressure effects in someone who may already be medicated, which is the one interaction eucommia has actually produced in a trial.

• Eucommia leaf with bark. Nishibe's group has proposed that the leaf's geniposidic acid might work in humans only with a phosphodiesterase inhibitor such as the bark's pinoresinol diglucoside. That is a hypothesis in a review, untested in any trial the author found, and no product has been formulated and studied on that basis.

Interactions & What NOT to Take

Blood pressure drugs

The only interaction the author found observed in people. In Tang's add-on trial, participants took eucommia capsules on top of calcium channel blockers (78 of 126 in the analysis set), ACE inhibitors or angiotensin receptor blockers (71), beta-blockers (38) and diuretics (11), and three of 68 randomized to the capsules developed hypotension that resolved on stopping. Named drugs in those classes include amlodipine, nifedipine, lisinopril, enalapril, losartan, valsartan, metoprolol, atenolol, hydrochlorothiazide and chlorthalidone. The same trial also found no additional pressure benefit in patients on calcium channel blockers, so the combination carries the downside without a demonstrated upside.

Beta-blockers specifically

Greenway's fat cell assay showed beta-adrenergic blocking activity. Combined with metoprolol, atenolol, propranolol, carvedilol or bisoprolol, a theoretical additive slowing of heart rate follows; it has not been studied.

Diuretics and lithium, as an inference

Nishibe's group reports that geniposidic acid "promotes natriuresis" in humans. Added sodium loss on a thiazide or loop diuretic (hydrochlorothiazide, furosemide) is a plausible additive effect, and lithium levels rise when sodium is lost. This is an untested inference from the leaf compound, flagged because the downside is serious, not because it has been seen.

Glucose-lowering drugs and anticoagulants

Named only: leaf extracts have glucose-lowering animal data (insulin, glipizide, glyburide), and monographs list a theoretical additive bleeding effect with warfarin, apixaban or clopidogrel. Neither has a eucommia-specific human report. Both topics are owned by other issues in this series.

Drug metabolism

The author found no PubMed-indexed study of eucommia bark or leaf against any cytochrome P450 enzyme or any named drug's pharmacokinetics. That means the question has not been asked, not that the answer is no.

What not to take it with

Any prescription antihypertensive without the prescriber's knowledge, or a second "blood pressure support" product.

Quality, Testing & Adulteration

The documented substitutes

Peng and colleagues (Chinese Traditional and Herbal Drugs 2013;44:3042) collected 12 market samples of false du zhong from eight species in four families and separated them from genuine bark by ITS2 DNA barcoding. The spindle-tree family, Celastraceae, supplied most: Euonymus fortunei (3 samples), E. japonicus (2), E. maackii (1) and E. myrianthus (1). Genuine samples from different sources formed a single clade, with the largest within-species genetic distance well below the smallest distance to any substitute, so the test works when someone runs it.

The substitution nobody calls adulteration

Leaf for bark. Leaf can be picked every year from standing trees, while bark has to be stripped from the trunk. Feng's 2023 data show leaf can carry enough pinoresinol diglucoside (up to 0.215 percent) to pass the bark's own HPLC minimum of 0.10 percent, and the rubber is present in both. A powdered capsule labeled "bark" therefore cannot be confirmed as bark by the bark's pharmacopeial assay alone. The discriminating evidence is the whole profile: leaf runs 2.6 to 6.2 percent chlorogenic acid (Feng, 2023), while the bark's monograph relies on lignans plus microscopic bark structure.

What third-party testing covers

The author found no USP-NF monograph and no ConsumerLab review for eucommia. A GMP or general verification seal does not establish species, plant part or processing state when no compendial method exists in that program. The methods do exist elsewhere: the HKCMMS monograph specifies microscopy of a transverse section and powder, TLC against pinoresinol diglucoside, an HPLC fingerprint with characteristic peaks, and limits for heavy metals, pesticide residues, mycotoxins and sulfur dioxide.

Questions to put to the seller

Ask for a lot-specific certificate that names Eucommia ulmoides Oliv., states "stem bark," says whether it is raw or salt-processed, and reports pinoresinol diglucoside by HPLC as a number against the 0.10 percent minimum. A credible supplier can also give a microscopy or DNA identity result, lead, cadmium, arsenic and mercury figures, and a sulfur dioxide result. If the product is an extract, the extract ratio, the solvent and the pinoresinol diglucoside percentage should all be on the certificate. A supplier who answers "eucommia extract" with no part and no percentage has not told you what is in the capsule.

What a buyer can check without a lab

Only whole bark can be checked by hand. A genuine piece is 2 to 7 mm thick, scraped smooth outside, dark purple and smooth inside, and pulls apart on fine silvery threads that stretch before they break. Salt-processed bark is darker and its threads are weaker (Zhu, 2024). Powder in a capsule shows none of this.

Special Considerations

Where the research numbers belong

These are the amounts the human studies used, kept here so they are not read as directions. Greenway: 500 mg of an 8 percent pinoresinol diglucoside bark extract three times daily (1.5 g) for 8 weeks, with no effect, and 1 g three times daily (3 g) for 2 weeks. Xu and Tang: six Quanduzhong capsules daily, 2.88 g of capsule contents representing 15 g of crude bark, an approved drug in China, taken under trial supervision. The Japanese leaf trials: one beverage a day with 80 to 85 mg of geniposidic acid. For scale, a 400 mg capsule of bark powder is about one thirty-seventh of the crude bark equivalent in the Quanduzhong regimen, and the author found no trial of it.

A claim with the parts swapped

Greenway's 2011 abstract opens by stating that "a tea made from Eucommia ulmoides leaves and bark is part of the Japanese diet." That sits oddly with the Japanese classification described above and with Kobayashi's leaf-only ingredient list. The sentence is a small example of the part substitution that runs through much of this literature: a bark trial justified by a leaf tradition.

Conservation and supply

The IUCN Red List assesses Eucommia ulmoides as Vulnerable (Rivers, 2018). Commercial bark and leaf come from cultivated trees; Quanduzhong's raw material, for example, comes from Good Agricultural Practice bases in Jinggangshan and Jishui, Jiangxi Province. A label claiming "wildcrafted" eucommia is claiming either material from a threatened wild population or something the label should explain.

Research Status & Evidence Quality

Tier 1, randomized human trials of bark

• Xu 2023: double-blind, placebo-controlled, 60 randomized, 58 treated, 4 weeks; 24-hour ambulatory pressure unchanged, office pressure lowered in the full analysis set, systolic not significant per protocol.

• Greenway 2011, Study 1: 24 randomized, 8 weeks, no difference.

• Greenway 2011, Study 3: 30 randomized, 2 weeks, 7.5/3.9 mmHg fall, comparator not stated in the abstract (against placebo, in 29, per Drugs.com's summary of the full paper).

• Jiang and colleagues, as cited by Xu 2023: sham-controlled, 12 weeks, office pressure lowered; not reviewed in full here.

• Tang 2025: open-label add-on, 136 randomized, 12 weeks, primary endpoints null, three hypotensive withdrawals.

Tier 1, randomized human trials of leaf

Three Japanese 12-week placebo-controlled beverage trials (85, 87 and 42 participants per NIBIOHN; Nishibe's review gives the third as 46) with systolic lowering in all three and diastolic lowering in one per NIBIOHN (Nishibe's review also reports it in the 80 mg trial); one Chinese 8-week trial of leaf extract capsules in 27 adults with abdominal obesity.

Tier 2, other human studies

Ten Chinese osteoporosis studies of eucommia preparations, nine of them combined with or compared against an active treatment and one a before-and-after metabolomics study, rated high risk of bias by the 2026 scoping review.

Tier 3, animal

Spontaneously hypertensive rats (Lang 2005; Gu 2010; Nishibe's geniposidic acid work), aged-model rats for collagen (Li 1998, 2000), collagenase tendinopathy in rats (Zhang 2026), and a 13-week toxicology study showing kidney injury that eased after dosing stopped at the lower dose and persisted at the higher (Luo 2020).

Tier 4, in vitro

Endothelium-dependent relaxation of rat and dog arteries (Kwan 2003), beta-adrenergic blockade in human fat cells (Greenway 2011), tenocyte protection by aucubin (Zhang 2026), and anti-inflammatory cytokine suppression in human immune cells by bark infusions and tinctures (Kołtun-Jasion and colleagues, Molecules 2025).

Research Limitations

• Part confusion. The two best-controlled sets of human data are on different plant parts with different chemistry, and secondary sources routinely merge them.

• Product specificity. Every bark trial used a single proprietary extract or approved drug product (an 8 percent extract, or Quanduzhong capsules). The author found no trial of plain bark powder, the form most US capsules contain.

• Endpoint inconsistency. Xu's office and ambulatory primary endpoints disagreed; Tang's primary endpoints were null and the positive finding is a 39-person subgroup.

• Manufacturer involvement. Quanduzhong's maker manufactured the capsules for both trials and has staff among the coauthors of both (four on Xu, three on Tang); the human leaf trials in Nishibe's review are, in its own words, "the reports of our research collaborators," and the Chinese leaf trial used extract prepared by Kobayashi Pharmaceutical.

Summary & Key Takeaways

Bottom Line

Eucommia bark is the rubber-threaded bark of a monotypic Chinese tree with a 2,000-year reputation for strengthening "sinew and bone" and a modern reputation for lowering blood pressure. The connective tissue reputation rests on rats. The blood pressure reputation rests on two pillars that do not support the same product: Japanese leaf beverage trials built on geniposidic acid, a compound largely destroyed when bark is dried, and a short list of small bark trials that used a standardized extract or a Chinese drug capsule and produced a mix of modest, inconsistent and null results. A plain bark-powder capsule inherits neither.

Key Safety Points

• In the one trial the author found of eucommia bark added to blood pressure medication, 3 of 68 people on the capsules developed hypotension and withdrew. Do not combine with antihypertensives without the prescriber's knowledge and home monitoring.

• Do not use in pregnancy. The traditional "calming the fetus" indication is not safety evidence.

• People with a latex allergy should avoid it, per an Australian Therapeutic Goods Administration safety alert.

• Rats dosed for 13 weeks developed dose-dependent kidney injury that did not fully reverse at the higher dose. People with kidney disease should not self-prescribe it.

• Beta-adrenergic blocking activity in human fat cells makes stacking with beta-blockers an untested combination.

• The author found no published drug-metabolism study of eucommia with any named drug.

Special Note

The bark's own identity test is a piece of rubber. Hong Kong's standard describes the broken bark's silvery elastic threads as an identifying feature. That rubber is the one property of Eucommia ulmoides that bark, leaf and fruit reliably share, while the blood pressure property a label implies depends on which part, which solvent and which processing the bottle never names.

Researched and drafted with AI assistance. Every claim verified against primary sources and human-reviewed before publication. Last reviewed: October 19, 2026. Corrections: reply to any issue.

This issue is educational and is not medical advice. If you take prescription medication, especially for blood pressure, or have a diagnosed condition, talk to a clinician before adding or stopping anything, including an herbal bark sold in a capsule.