Black Haw

What is Black Haw?

Black haw is the bark of Viburnum prunifolium L., a shrub or small tree reaching 2 to 9 meters that grows from Connecticut west to eastern Kansas and south to Alabama and Texas. It was an official drug of the United States Pharmacopoeia from 1882 until it was dropped at the tenth revision in 1926, sold then and now for menstrual cramping, threatened miscarriage and pelvic pain. The 1905 National Standard Dispensatory, writing for physicians who prescribed it daily, summarized the drug in nine words: "The virtues attributed to viburnum prunifolium are as feeble as they are numerous."

Common Names

• Black haw, blackhaw, blackhaw viburnum

• American sloe, sloe-leaved viburnum, stag bush, stagberry

• Nannybush, sweet haw

• Viburnum prunifolii cortex, the old pharmaceutical name

• Sometimes sold as "American cramp bark," which invites confusion with Viburnum opulus

Primary Active Compounds

• Scopoletin, a 7-hydroxy-6-methoxycoumarin, reported in root bark at 4 to 90 ppm

• Aesculetin (esculetin) and its glycosides scopolin and aesculin

• Four iridoid glucosides with a Valeriana-type skeleton: 2'-O-acetyldihydropenstemide, 2'-O-trans-p-coumaroyldihydropenstemide, 2'-O-acetylpatrinoside and patrinoside

• Amentoflavone, a biflavone reported in V. prunifolium but not in V. opulus

• Triterpenes: oleanolic acid, ursolic acid, their acetates, alpha- and beta-amyrin, beta-sitosterol

• Arbutin, chlorogenic and isochlorogenic acid, catechin

• Valeric and isovaleric acid, the latter at up to 130 ppm in root bark

• Tannin, up to 20,000 ppm in root bark, and 2.5 percent bitter resin

• Oxalic, citric and malic acids

• 1-Methyl-2,3-dibutyl hemimellitate, characterized by Jarboe and colleagues in 1969 and attributed specifically to stem bark

Key Note

"Viburnin," which appears on retailer chemistry lists to this day, is not a defined molecule. Herman van Allen described it in the American Journal of Pharmacy in 1880 as a greenish-yellow bitter resin, and Kramer named it. No structure was ever assigned. A century and a half later it is still being listed as an active constituent by sellers who have never seen a chromatogram of it.

Black haw is a genuinely interesting piece of American pharmacognosy with a documented smooth-muscle relaxant chemistry and, as of August 2026, not one controlled clinical trial in humans.

Primary Functions & Benefits

Every function attributed to black haw comes from one of three sources: 19th century clinical impression, mid-20th century isolated-tissue pharmacology, or the 2009 Cometa study on rabbit and guinea-pig tissue. Nothing on this list has been tested in a randomized human trial.

Uterine and smooth-muscle relaxation. Jarboe and colleagues, publishing in Nature in 1966 (volume 212, issue 5064, page 837), obtained complete relaxation of isolated rat uterus with methanolic extracts of both V. prunifolium and V. opulus. They concluded the effect was direct on the muscle rather than sympathomimetic.

Beta-adrenergic mediated relaxation. Cometa and colleagues (Journal of Ethnopharmacology, 2009, volume 123, pages 201 to 207) reached the opposite mechanistic conclusion. Propranolol at 10⁻⁶ M abolished every relaxant effect they measured, which points to beta-receptor mediation rather than direct myocyte action.

Astringency. The tannin content, up to 2 percent of root bark, is real and explains the historical use in diarrhea and as a gargle.

Mild hypotensive action. R. L. Payne reported marked lowering of arterial pressure in animals given large doses. The related compound viopudial, isolated from V. opulus by Nicholson, Darby and Jarboe (Proceedings of the Society for Experimental Biology and Medicine, 1972, volume 140, pages 457 to 461), is described as hypotensive and antispasmodic.

Forms & Standardization

There is no standardization. No pharmacopoeial assay exists for black haw anywhere in the world today, no marker compound has an accepted minimum, and no commercial product is sold to a percentage specification. What follows is what is actually on sale.

Cut and sifted dried bark. The bulk form. Typical retail pack sizes run 1 ounce to 1 pound. Almost universally labeled "Black Haw Bark, Viburnum prunifolium," wildcrafted, with no plant part named. Mountain Rose Herbs, Dragon Herbarium, Glenbrook Farms, Wild Spirit Herbals, Forest & Meadow and Gaia Garden all sell it this way.

Powder. American Botanicals, a MartinBauer company supplying the trade, lists the item as "Black Haw Tree Bark Powder." That is the industrial supply chain naming the part, and the part is not root.

1:5 tincture. The dominant liquid format. Herb Pharm's black haw is 1:5 in certified organic cane alcohol at 52 to 62 percent, an extraction rate of 140 mg of herb per 0.7 mL, ingredient declared as "Black Haw stem and root bark." Practitioner references give 1:5 at 60 to 70 percent ethanol dosed at 5 to 10 mL three times daily.

1:3 tincture. Napiers of Edinburgh sells black haw at 1:3 in 45 percent sugar-beet ethanol, a stronger ratio in a weaker menstruum, which shifts the extract toward the water-soluble iridoids and away from the resin fraction.

1:1 fluid extract. Historically the preferred form because, as the 1918 US Dispensatory noted, the solid extract loses volatile acid on evaporation. The USP fluidextract used a 67 percent alcohol menstruum. Modern practitioner dosing is 4 to 8 mL of 1:1 in 70 percent ethanol, three times daily.

Glycerite. Hawaii Pharm and Herbal Terra sell alcohol-free versions declaring roughly 983 mg of dry bark equivalent per serving. Glycerin is a poor solvent for the triterpenes and the resin fraction, which is 2.5 percent of the drug by weight, so a glycerite is chemically a different preparation from a 60 percent ethanol tincture of the same bark.

Capsules. TerraVita sells 450 mg capsules of "Black Haw Bark." Secrets of the Tribe sells 400 mg capsules explicitly declaring "dried root bark," one of the very few products in the market that names the traditional part.

Combination formulas. This is where most black haw is actually consumed. Herbs Etc. Menstrual Cramp ReLeaf lists "Black Haw (stem bark) extract" alongside cramp bark, bethroot, clove, cinnamon, fresh wild yam, cardamom and orange peel in an undisclosed proprietary blend. Nature's Sunshine Menstrual Reg, Crystal Star Muscle Relax, Doctor Morse's Female Reproductive Tonic and Mountain Meadow Herbs Preterm Pregnancy Support all list black haw with no part and no amount.

The historical solid extract. For comparison, the USP powdered extract was made by percolating 100 g of drug with diluted alcohol, incorporating 5 g of magnesium oxide and enough dried starch to bring the product to 20 g, so 1 g of extract represented 5 g of bark. Dose was 3 to 10 grains.

What the extract ratio does not tell you. A 1:5 tincture of root bark and a 1:5 tincture of trunk bark are the same number on the label and different products in the bottle. Dr. Duke's Phytochemical Database, which indexes constituents by plant part, attributes amentoflavone, arbutin, beta-sitosterol, oleanolic acid acetate, ursolic acid acetate, oxalic acid and the resin fraction to root bark, and attributes exactly two entries to stem bark: 1-methyl-2,3-dibutyl hemimellitate and a generic volatile organic acids listing. Scopoletin, the most-cited active, is quantified only for root bark, at 4 to 90 ppm. That is a 22-fold range within a single named plant part, before you even ask which part you bought.

Food Sources

Black haw is not a food, but the plant is not entirely absent from the food supply and the distinction matters legally.

• The berries, ovoid blue-black drupes ripening in late summer and sweetening after frost, are edible and were eaten raw or made into preserves. They contain a single stony seed. No nutrient composition data has been published for them.

• The bark is listed in 21 CFR 172.510 as a permitted natural flavoring substance under the entry "Haw, black, bark, Viburnum prunifolium L." It carries FEMA number 2538 and CAS 84929-54-4. Viburnum opulus is not on that list.

• The leaves were used as a tea substitute according to King's American Dispensatory, 1898.

• Scopoletin and umbelliferone are recorded in the fruit juice, not just the bark.

Food use here is a flavoring at trace levels in beverages and confectionery, not a therapeutic route. Nobody is getting a pharmacological dose of black haw from food, and the FDA flavor listing tells you nothing about the safety of 5 mL of a 1:5 tincture three times a day.

Who Should Take Black Haw

Given that the human evidence is zero controlled trials, the honest answer is that nobody has an evidence-based reason to take it. What can be said is who has historically used it and what the plausible case looks like.

• People with spasmodic dysmenorrhea, meaning cramping, colicky, intermittent menstrual pain rather than steady ache, who have already tried and rejected NSAIDs. This was the single most consistent 19th century indication and the one the isolated-tissue data most nearly supports.

• People who tolerate cramp bark and want the more bitter, more resinous relative. The American Herbal Pharmacopoeia notes that black haw is often used as a less expensive substitute for cramp bark, though it is separately respected in its own right.

• People working with a practitioner who can name the plant part, the extract ratio and the supplier. Without those three facts, the product is not identifiable.

Anyone taking it should treat the first bottle as a trial of one and should not expect it to behave like the last bottle from a different brand.

Who Should AVOID or Use Caution

Contraindications

• Pregnancy without direct practitioner supervision. This is the sharpest problem in the category, because black haw is still marketed for exactly this use. Mountain Meadow Herbs sells a product called Preterm Pregnancy Support containing it. The strongest historical claim, that it prevents miscarriage, was doubted by Harvey Wickes Felter, one of the two authors of King's American Dispensatory, writing in his 1922 Eclectic Materia Medica: "we have utterly failed in every attempt to prevent miscarriage with the agent where there was any considerable hemorrhage."

• Documented aspirin or salicylate allergy, on the precautionary principle. See the note below on how small the salicin content actually is.

• Known allergy to Viburnum species.

Use Caution

• History of calcium oxalate kidney stones. Oxalic acid was identified in the bark by van Allen in 1880, and the USP microscopic description of the powder specifies calcium oxalate crystals from 0.015 to 0.035 mm, mostly as rosette aggregates, plus occasional monoclinic prisms. No one has ever published a milligrams-per-gram oxalate figure for the bark. The caution is real and unquantified.

• Anyone on antihypertensives, given Payne's animal finding of marked arterial pressure reduction.

• Anyone on anticoagulants, again precautionary rather than demonstrated.

• Children and adolescents, on the same salicylate logic that governs aspirin.

Critical Safety Point

The salicin caution is repeated on nearly every black haw product page and it deserves a number. Where salicin has been quantified in black haw root bark at all, the figure is 2.2 ppm, which is 2.2 mg per kilogram. A 4 g dose of bark at that concentration delivers about 8.8 micrograms of salicin. The willow bark trial by Schmid and colleagues (Phytotherapy Research, 2001, volume 15, pages 344 to 350, n equals 78) used 240 mg of salicin per day. Hörhammer, Wagner and Reinhardt (Zeitschrift für Naturforschung B, 1967, volume 22, pages 768 to 776) reported the absence of salicin from black haw bark entirely, contradicting earlier work. So the salicylate warning is either a trace-level theoretical risk or a warning about a compound that is not there. Neither version supports the confident phrasing on the labels, and neither is the reason to be careful in pregnancy.

Recommended Dosages

Dried bark, decoction or infusion

• USP dose, 30 to 60 grains, which is 2.0 to 3.9 g

• Felter 1922, 5 to 60 grains, 0.32 to 3.9 g

• Modern practitioner references, 2.5 to 5 g three times daily

• Traditional decoction, simmer 1 teaspoon in 2 cups of water for 15 to 25 minutes

1:5 tincture, 60 to 70 percent ethanol

• 5 to 10 mL three times daily

• At Herb Pharm's stated extraction rate of 140 mg herb per 0.7 mL, 5 mL delivers about 1 g of dried herb

1:1 fluid extract, 70 percent ethanol

• 4 to 8 mL three times daily

• Historical USP fluidextract, half to one fluidrachm, 1.8 to 3.75 mL

Specific medicine (Eclectic preparation)

• Felter and Ellingwood both give 5 to 60 drops, which is a twelve-fold range and reflects how little anyone knew about the effective dose

Duration

There is no trial-based duration because there are no trials. Historical Eclectic practice for dysmenorrhea was to start two to four days before the expected period and continue through it, meaning roughly 5 to 8 days per cycle. For habitual miscarriage, Ellingwood in 1919 described dosing for one to two weeks before the expected event, a regimen that has no modern evidentiary support and should not be reproduced. Nothing in the record supports continuous year-round use.

Timing & Administration

• Taken away from meals in most traditional protocols, largely because the tannin fraction binds dietary protein and iron.

• For menstrual cramping, dosing begins before the pain, not during it. Every Eclectic source is consistent that starting after cramping is established gives worse results than starting 48 to 96 hours ahead.

• Divided across the day, three to four times, matching the fact that the coumarins and iridoids are small, water-soluble molecules with no depot effect.

• Alcohol tinctures are more complete extractions than glycerites for the resin and triterpene fraction. If the reason for choosing black haw over cramp bark is its higher resin content, 2.5 percent versus roughly a third of that in V. opulus, a glycerite defeats the point.

• Bark should be stored dry in paper or cardboard, never plastic. Suppliers who buy it wholesale specify this because the bark molds.

Timeline of Effects

There is no pharmacokinetic study of black haw in humans. No Cmax, no half-life, no bioavailability figure exists for scopoletin or any of the four iridoids as delivered from this plant. What follows is bounded by the tissue work and the historical record.

• Minutes to hours. In isolated tissue, relaxation is prompt. Cometa's cumulative-concentration protocol on rabbit jejunum and carbachol-precontracted guinea-pig trachea ran over minutes at 1 to 100 micrograms per mL of extract. Whether anything comparable happens in a human uterus after an oral dose is unknown.

• One cycle. The fair trial for dysmenorrhea is one full menstrual cycle with dosing started before onset. If there is no perceptible difference in cramp character across that cycle, there is no reason to expect a second one to differ.

• Two to three cycles. The outer limit worth spending money on. Historical practice used it for months, but historical practice also included Shennan's 1896 self-experiment in which he took six drachms, roughly 22 mL, of the fluidextract within thirty minutes and observed no demonstrable effect beyond a doubtful decrease in pulse rate and force.

• When to conclude it is not working. After two cycles. Pilcher, publishing in the Archives of Internal Medicine in January 1917, reported that at the doses ordinarily employed black haw had no effect of any kind on uterine muscle. That finding is 109 years old and has never been overturned by a controlled human study.

Benefits of Taking Black Haw

Stated plainly: not one claimed benefit of black haw has ever survived a controlled test in people. What exists is a consistent traditional record and a coherent, if contested, preclinical mechanism.

• Spasmodic menstrual pain. The convergent claim across King's 1898, Ellingwood 1919 and Felter 1922, all describing relief of cramp-like, intermittent, expulsive pelvic pain specifically rather than steady pain.

• Smooth-muscle spasm generally. The 2009 tissue data was collected in gut and airway, not uterus. If the beta-adrenergic mechanism is correct, the plant is a weak, non-selective smooth-muscle relaxant rather than a uterine-specific agent, which would explain the traditional uses in intestinal colic, biliary colic and asthma.

• Astringent effect in diarrhea. The one action with an uncontroversial chemical basis, tannin at up to 2 percent of the root bark.

• Leg cramps at night. Both King's and Felter single this out. No modern data.

Potential Negatives & Side Effects

• Nausea and vomiting at large doses. King's American Dispensatory, 1898: "Large doses sometimes produce nausea and vomiting." This is the most consistently reported adverse effect across the historical literature.

• Dry mouth, headache and visual disturbance at very large doses, reported in the practitioner literature without a threshold dose attached.

• Gastrointestinal upset from tannin, predictable at decoction doses of 5 g three times daily.

• Reduced iron absorption, the standard consequence of a 2 percent tannin herb taken with meals.

• Potential blood pressure reduction. Payne's animal work and the viopudial data from the sister species both point this way. Nobody has measured it in humans.

• Product-to-product inconsistency. The most common real-world negative. A consumer who responds to one brand's bark has no way to reproduce that result with another brand's, because the two may be different plant parts from different Viburnum species.

Deficiency Symptoms

Black haw is not an essential nutrient and there is no black haw deficiency. Nobody has a requirement for scopoletin, amentoflavone or patrinoside, no intake level has ever been associated with a deficiency syndrome, and no reference intake exists in any country.

What black haw addresses

A symptom, specifically spasmodic pelvic pain, not a nutritional gap. Primary dysmenorrhea affects a large share of menstruating people and has well-characterized drivers, principally prostaglandin F2-alpha driven myometrial contraction and ischemia. Black haw does not correct a shortage of anything. If it works, it works as a weak pharmacological agent.

Bottom line

Comparing black haw to iron or iodine is a category error. There is no blood test, no functional marker and no population survey that could ever show a black haw deficit, because there is nothing to be deficient in.

Toxicity Symptoms

At high intake

Nausea and vomiting come first, and in practice they cap the dose before anything else happens. Payne's animal work, cited in the 1918 US Dispensatory, describes what a genuinely toxic dose does in laboratory species: progressive muscular weakness ending in complete paralysis with loss of reflex action, attributed to action on the motor side of the spinal cord, plus marked lowering of arterial pressure attributed to direct cardiac action. No equivalent human syndrome has ever been documented.

Signs to reduce or stop

• Persistent nausea, vomiting, or abdominal cramping

• Light-headedness on standing, which would be consistent with the hypotensive effect

• Headache with visual disturbance

• Any new flank pain in someone with a stone history, given the unquantified oxalate load

• Any rash or respiratory symptom in a salicylate-sensitive person

General note

The realistic hazard with black haw is not overdose. It is that a product marketed for use during pregnancy has no human safety data of any kind, no identified plant part, no assay, and no controlled trial establishing that it does anything. Shennan swallowed 22 mL of the fluidextract in half an hour in 1896 and recorded essentially nothing. A substance that weak is unlikely to poison you and equally unlikely to help you.

How Black Haw Works

Two mechanisms have been proposed, by two research groups, forty-three years apart, and they contradict each other.

The coumarin, direct-muscle hypothesis. Jarboe and colleagues published the Nature paper in 1966 showing complete relaxation of isolated rat uterus, then isolated scopoletin as an antispasmodic component of both V. opulus and V. prunifolium (Journal of Medicinal Chemistry, 1967, volume 10, pages 488 to 489). Their conclusion was that black haw acts directly on the smooth muscle cell and is not sympathomimetic. Scopoletin is a coumarin, and coumarins of this class relax smooth muscle through phosphodiesterase inhibition and calcium handling effects rather than through a receptor. The same group went on to characterize 1-methyl-2,3-dibutyl hemimellitate from the plant in 1969 and viopudial from V. opulus in 1972.

The iridoid, beta-adrenergic hypothesis. Cometa and colleagues in 2009 isolated four Valeriana-type iridoid glucosides and tested them on rabbit jejunum spontaneous contractions and on guinea-pig trachea precontracted with carbachol at 5.5 x 10⁻⁷ M. The ethyl acetate fraction was more potent than the butanol fraction, which was more potent than the crude methanol extract, and within compounds the order was 2'-O-acetyldihydropenstemide, then 2'-O-trans-p-coumaroyldihydropenstemide, then 2'-O-acetylpatrinoside, then patrinoside. By HPLC the first two made up 7.38 percent and 14.90 percent of the ethyl acetate fraction, the second two 18.47 percent and 8.86 percent of the butanol fraction. The decisive result: propranolol at 10⁻⁶ M antagonized every relaxant and spasmolytic effect they observed, and at a non-relaxing 0.5 micrograms per mL the extract potentiated isoprenaline. That is a beta-adrenergic signature, not a direct myocyte effect.

What this means for a buyer. Whichever mechanism is right, both sets of actives are minor constituents. Scopoletin at 4 to 90 ppm in root bark is 0.0004 to 0.009 percent of the raw material. The four iridoids were quantified as percentages of purified solvent fractions, not of the bark. Nobody has published how much of any of them is in a gram of commercial black haw, and nobody assays for them. The mechanism sections on retail websites describe chemistry that has never been measured in the product being sold.

Synergistic Supplements

• Cramp bark, Viburnum opulus. The standard pairing and the most defensible one, since both species share scopoletin and the same broad triterpene profile. Cramp bark was itself USP official from 1890 to 1910, defined explicitly as "the dried bark (of the stem)." It contains roughly a third as much resin as black haw. Herbs Etc. combines the two in a single formula.

• Wild yam, Dioscorea villosa. A traditional antispasmodic pairing with no human data behind the combination.

• Magnesium. Has actual randomized evidence in primary dysmenorrhea, unlike black haw, which makes it the more sensible first move.

• Ginger, Zingiber officinale. Multiple small randomized trials in dysmenorrhea at 750 to 2,000 mg per day. If someone wants a botanical for menstrual pain with human data attached, this is it.

• Hawthorn, Crataegus species. Combined with black haw by midwives for gestational hypertension. Note that the shared word "haw" is coincidence, not kinship. Crataegus is in the Rosaceae, an entirely different family.

Interactions & What NOT to Take

• Antihypertensives, including amlodipine, lisinopril and metoprolol. Payne's animal data showed marked arterial pressure reduction and the sister-species compound viopudial is characterized as hypotensive. Additive effect is plausible and unstudied.

• Beta-agonists such as salbutamol and formoterol, and beta-blockers such as propranolol and atenolol. This follows directly from Cometa's finding that propranolol blocked the herb's effects and that the extract potentiated isoprenaline. If the beta-adrenergic mechanism is real, black haw sits in the same pharmacological space as those drugs.

• Warfarin, apixaban, clopidogrel and aspirin. The standard salicylate caution. Weak, given the salicin numbers above, but the coumarins are a separate and less examined question, since scopoletin is a coumarin even though it is not an anticoagulant coumarin like dicoumarol.

• Iron supplements and thyroid hormone. Separate by at least two hours from any tannin-rich decoction.

• Anything taken during pregnancy. Not a drug interaction so much as a category refusal. There is no safety dataset.

Quality, Testing & Adulteration

This is where black haw is genuinely worse than most of the shelf, and the reason is that the failure mode is not fraud.

Documented species substitution, going back 120 years. John Uri Lloyd reported in the Pharmaceutical Review (volume 23, page 333) that the bark of all native Viburnum species is collected by root diggers and sold as black haw. Farwell reported a commercial sample that was much darker than the official bark and consisted largely of stem bark from an unspecified Viburnum. The 1905 National Standard Dispensatory stated that a large part of the bark collected in the Southern States must come from Viburnum rufotomentosum Small, now called V. rufidulum, a species only recently separated from prunifolium at the time. V. dentatum was also reported in commerce as black haw. The USP itself accepted V. lentago as equally official from 1905 onward, so two different species were legally the same drug.

The plant part problem, which is not adulteration at all. Root bark and stem bark differ in taste, in microscopy and in chemistry. The 1905 monograph records that root bark tastes very bitter where the drug generally tastes merely bitter, and that stem bark powder contains many more bast fibers. Dr. Duke's database assigns amentoflavone, arbutin, beta-sitosterol, the triterpene acetates and the oxalic acid to root bark; scopoletin is quantified only in root bark; the one compound uniquely assigned to stem bark is 1-methyl-2,3-dibutyl hemimellitate. Yet the wholesale trade sells the material as tree bark. Root Buyer, a company that buys wild-harvested botanicals from diggers, lists black haw under "Parts Used: Tree Bark" and instructs harvesters to collect "the bark from the limbs and the trunk," to peel only one side of the trunk, and to prune branches for peeling so the shrub survives for future harvest. The same company's catalog lists "Devils Club Root Bark" as a separate line item, so they clearly say root bark when they mean it.

What actual labels say. In the NIH Dietary Supplement Label Database, 70 labels list black haw. Forty name no plant part whatsoever. Eighteen say "bark" with no qualifier. Nine, all from Herb Pharm, say "stem and root bark." Three, all from Herbs Etc., say "stem bark." Zero say root bark alone. Across roughly 17 live retail listings checked directly, the pattern was the same: Mountain Rose Herbs, Dragon Herbarium, Glenbrook Farms, Herbs from the Labyrinth, Wild Spirit Herbals, Forest & Meadow, The Herb Shoppe, Napiers, Hawaii Pharm and Herbalist & Alchemist all say "bark." American Botanicals says "tree bark." Only Secrets of the Tribe's 400 mg capsules say "dried root bark." Gaia Garden manages to have it both ways, titling the product "Black Haw Bark" while instructing buyers to decoct "1 teaspoon of Black Haw Root Bark."

What no standard covers. There is no USP-NF monograph for Viburnum prunifolium today. There is no European Medicines Agency HMPC monograph. The German Commission E, which issued 380 herbal monographs between 1978 and 1994, never addressed it. The only modern analytical monograph is the American Herbal Pharmacopoeia's, and it is titled "Black Haw Bark," not root bark, in a series that names other entries "Blue Cohosh Rhizome and Root," "Echinacea purpurea Root" and "Hawthorn Leaf and Flower." AHP's own product description says the practical way to distinguish black haw from cramp bark is that the two powders have different colors and aromas. That is organoleptic identification, and it distinguishes species, not plant parts.

What a certificate of analysis can and cannot show. Ask for one and you will get botanical identity, usually by macroscopic or TLC comparison, plus heavy metals, microbial limits and pesticide residues. You will not get a plant part determination, because no validated method for it is in routine commercial use, and you will not get a scopoletin or iridoid assay, because no specification exists to test against. Microscopy could in principle distinguish root bark from stem bark by bast fiber density, exactly as the 1905 monograph described, but no laboratory offers that as a standard service and no buyer asks for it.

What a buyer can actually verify. Less than the label implies. You can confirm the Latin binomial. You can confirm the extract ratio and solvent. You can confirm whether the label names a plant part, which for 58 of 70 database labels it does not. Beyond that, two bottles carrying identical text can contain root bark, trunk bark, limb bark, or a different Viburnum species entirely, and no seller is lying.

Special Considerations

Pregnancy. Black haw's entire reputation rests on preventing miscarriage, and that reputation has an ugly history. King's American Dispensatory records, quoting Scudder, that it was "customary for planters to compel their female slaves to drink an infusion of black haw daily whilst pregnant to prevent abortion, from taking the cottonroot." That is the historical foundation of the modern marketing claim. It is worth stating that Felter, an Eclectic physician writing in 1922 with every professional incentive to defend the drug, said his own experience led him to doubt it.

Sustainability. Root bark harvest is destructive in a way stem bark harvest is not. A shrub whose roots are dug and stripped does not regrow; a shrub whose branches are pruned and peeled does. Black haw is not on the United Plant Savers At-Risk or To-Watch lists, so the pressure is currently manageable, but the economic incentive runs the wrong way: the cheaper, easier, non-destructive harvest is also the one the pharmacopoeias explicitly did not want.

Species confusion with cramp bark. V. opulus is European in origin and its US commercial supply has historically included V. trilobum. The two species are used interchangeably by many practitioners, and AHP notes black haw is often the cheaper substitute for cramp bark, which means substitution pressure runs in a specific direction.

Name confusion with hawthorn. Black haw and hawthorn share three letters and nothing else. Crataegus is Rosaceae with a large cardiovascular trial literature. Viburnum prunifolium is Viburnaceae with none.

Taxonomy. The plant is most often printed as Adoxaceae, and older sources say Caprifoliaceae. The currently correct family name is Viburnaceae Raf., because the 2008 proposal to "superconserve" Adoxaceae against the older name Viburnaceae failed. Kew's Plants of the World Online and the Flora of the Southeastern United States both use Viburnaceae.

Research Status & Evidence Quality

Strong Evidence For

Nothing. There is no indication for which black haw has strong evidence in humans. A PubMed search for "Viburnum prunifolium" in August 2026 returns 24 records in total, and filtering those for clinical trial or randomized controlled trial publication types returns zero. Several of the 24 are entomology and plant taxonomy papers, and eight are letters and case reports from the Southern Medical Record, the Atlanta Medical and Surgical Journal and the British Medical Journal published between 1878 and 1886.

Moderate Evidence For

Nothing meets this bar either. The strongest available evidence is in vitro, in three species of laboratory animal tissue, from two research groups.

Emerging / Preliminary Evidence For

• Smooth-muscle relaxation in isolated rabbit jejunum and guinea-pig trachea, Cometa 2009, with a beta-adrenergic mechanism supported by propranolol blockade at 10⁻⁶ M

• Uterine relaxation in isolated rat uterus, Jarboe 1966, with a proposed direct-muscle mechanism

• Scopoletin as an antispasmodic constituent, Jarboe 1967

• Iridoid glucoside chemistry, Tomassini and colleagues, Planta Medica, 1999, volume 65, page 195

• Constituent identification including amentoflavone, Hörhammer, Wagner and Reinhardt, 1967

Research Limitations

• Zero randomized controlled trials of any size, in any indication, in any country.

• Zero human pharmacokinetic data. No absorption, distribution or elimination figure exists for any black haw constituent as delivered from the plant.

• The two mechanistic studies contradict each other on whether the action is receptor-mediated.

• No published study specifies whether it used root bark or stem bark. Cometa 2009 says "the drug" and "dried bark." The one modern pharmacology paper on the plant does not record the variable this article is about.

• The 1917 Pilcher finding, that ordinary doses have no effect on uterine muscle, has never been formally rebutted in humans.

• The 1896 Shennan self-experiment at roughly 22 mL of fluidextract found essentially nothing.

• Contemporary skepticism existed. A. G. Smythe published "Viburnum Prunifolium Unreliable in Abortion: A Rejoinder" in the Southern Medical Record on 20 March 1882, four months before the drug entered the Pharmacopoeia.

Summary & Key Takeaways

Black haw is a real medicinal bark with a real chemistry, a 148-year published history, and no clinical evidence at all. It entered the United States Pharmacopoeia in 1882, left it in 1926, and in the century since has accumulated exactly two mechanistic papers that disagree with each other and not one controlled trial in a human being. The strongest single fact in its file is negative: Pilcher reported in 1917 that at ordinary doses it does nothing measurable to uterine muscle, and nobody has ever shown otherwise.

Bottom Line

The word "bark" on a black haw label is not a specification, it is a gap. The pharmacopoeias that took this plant seriously said root bark, and the 1905 USP said it in exactly those words. The trade sells tree bark, the label says bark, and the difference is invisible to the buyer, unmeasured by any certificate of analysis, and not considered adulteration by anyone, because the label is technically accurate.

Key Safety Points

• Do not use in pregnancy without practitioner supervision, notwithstanding that the entire historical claim is about pregnancy

• Caution with a calcium oxalate stone history, on a genuine but never quantified oxalate content

• The salicin warning that appears everywhere is based on a maximum of 2.2 ppm in root bark, roughly 8.8 micrograms in a 4 g dose, against 240 mg of salicin per day in the willow bark trial literature, and one 1967 paper found no salicin at all

• Possible additive hypotensive effect with blood pressure medication

• Nausea and vomiting are the dose-limiting effects at high intake

Special Note

Plant part is the quietest variable in the herbal aisle. Species substitution gets written up, mislabeled dosage gets litigated, and heavy metals get tested. But when the pharmacopoeia specified root bark and the label says bark, nothing has been falsified and no rule has been broken, so nobody looks. The tell is easy to check and worth carrying to every other bark, root and rhizome on the shelf: find the historical monograph, read what part it made official, then read what your bottle says. If the bottle is less specific than a book written in 1905, that vagueness was a choice, and it was made by someone who knew which part was cheaper to harvest.