Safety, Interactions and Sustainability

Devil's claw is one of the better-tolerated herbal anti-inflammatories — in the four-month trial against diacerein it produced fewer adverse events than the pharmaceutical it was tested against. That is the headline, and it is real. But “well tolerated on average” is not the same as “safe for everyone,” and devil's claw has a specific list of people who should not take it. Two entries on that list — peptic ulcer disease and cardiac rhythm disorders — follow directly from what the herb does in the body rather than from generic caution.

This article also covers something most supplement pages skip: where devil's claw comes from. It is wild-dug from the Kalahari, its conservation status has been formally contested at an international treaty conference, and the income from harvesting it matters enormously to some of the poorest rural communities in southern Africa. Those facts belong on the same page as the dosing advice.

Table of Contents

1. The Overall Safety Picture
2. Gastrointestinal Upset — the Commonest Adverse Effect
3. Peptic Ulcer Disease, Gastritis and Reflux
4. Gallstones and Bile-Duct Disease
5. The Cardiac Caution — What the Animal Data Actually Show
6. Warfarin, Anticoagulants and Bleeding
7. P-Glycoprotein, CYP Enzymes and Other Medicines
8. Pregnancy, Breastfeeding and Children
9. Diabetes, Blood Pressure and Surgery
10. Who Should Not Take Devil's Claw
11. Sustainability — the Part Nobody Puts on the Label
12. Buying Well
13. Key Research Papers
14. Connections

The Overall Safety Picture

A systematic review specifically devoted to the safety of devil's claw preparations in osteoarthritis and low back pain concluded that the adverse events recorded in the clinical literature were predominantly minor, and predominantly digestive. The individual trials bear that out:

• In the four-month randomised trial against diacerein (122 patients), adverse events were significantly less frequent on devil's claw. Diarrhoea — the commonest complaint in both arms — occurred in 8.1 percent on devil's claw versus 26.7 percent on the drug, and patients' own tolerance ratings favoured the herb.
• In the 250-patient Doloteffin surveillance study, about 10 percent of patients had minor adverse events possibly attributable to the extract.
• In the 75-patient 12-week study, only two possible adverse drug reactions were reported in the whole cohort: dyspepsia, and a sensation of fullness.
• In the 197-patient placebo-controlled trial, the authors found no evidence of extract-related side effects except mild and infrequent gastrointestinal symptoms.
• In the 259-patient UK open study, safety was assessed by self-report plus blood analysis and liver function tests, and the findings were reassuring.

Set against that, one limitation applies to all of it: the trials were four weeks to four months long. Open follow-up out to a year exists, but there is no randomised evidence on taking devil's claw continuously for years. Rare adverse effects and slow-developing ones are exactly what short trials in a few hundred people cannot detect. Formal toxicology work on aqueous-alcohol extracts has been published, but the human long-term picture rests largely on the absence of alarming reports rather than on positive evidence of long-term safety. Those are different things.

Gastrointestinal Upset — the Commonest Adverse Effect

Across every study, the same complaints recur: diarrhoea, loose stools, nausea, stomach discomfort, a sense of fullness. In the comparative trials the rate ran at roughly 8 to 10 percent — common enough that you should expect it as a possibility, mild enough that most people carry on.

This is not a mystery side effect. Devil's claw is an intensely bitter herb, and bitters act on the digestive tract by design: they stimulate salivary flow, gastric acid secretion and bile release. The traditional European indication for devil's claw — recognised in the EMA monograph — is precisely mild digestive disorders such as bloating and flatulence and temporary loss of appetite. The digestive side effect and the digestive indication are the same pharmacology pointed in different directions.

Practical management:

• Take it with food. This is the single most effective fix and works for most people.
• Build the dose up over a week rather than starting at full strength. There is no benefit to loading — the herb takes weeks to act regardless.
• Split doses across the day. Every trial dosed two or three times daily; a single large dose is harder on the stomach.
• If diarrhoea persists, stop. Persistent diarrhoea is not something to push through, particularly in older adults where dehydration and electrolyte loss matter, and particularly if you take diuretics or digoxin.

Less frequently reported effects include headache, dizziness, tinnitus and allergic skin reactions. Allergy is a real if uncommon possibility — stop immediately for rash, swelling or breathing difficulty.

Peptic Ulcer Disease, Gastritis and Reflux

This is the caution with the clearest mechanistic basis. Devil's claw stimulates gastric acid secretion. That is how bitters work and it is why the herb has a traditional appetite and digestion indication.

If you have an active gastric or duodenal ulcer, erosive gastritis, or significant gastro-oesophageal reflux, extra acid is the last thing the tissue needs. Standard herbal reference sources and regulatory monographs list peptic ulcer as a contraindication, and the reasoning holds up: you would not take a drug that raised acid output into an ulcer, and the same logic applies to a plant that does it.

Two situations deserve individual thought:

• You are on a proton-pump inhibitor because an NSAID upset your stomach. This is extremely common in osteoarthritis. Adding an acid-stimulating bitter while taking an acid-suppressing drug is working against yourself in both directions. Raise it with your prescriber before starting.
• You had an ulcer that has healed. Not an absolute bar, but a reason to start low, take every dose with food, and stop at the first sign of epigastric pain.

There is an interesting wrinkle worth flagging honestly: some animal work has reported gastroprotective rather than ulcerogenic effects for devil's claw extracts, and a cell study found devil's claw root extract modulated the ghrelin receptor in a way suggesting appetite suppression — which sits oddly against the traditional appetite-stimulant use. The pharmacology here is less tidy than either the traditional claim or the standard warning suggests. Until that is resolved in humans, the conservative reading applies: if you have an active ulcer, do not take it.

Gallstones and Bile-Duct Disease

Devil's claw also stimulates bile flow — part of the same bitter-tonic action. For most people that is either neutral or mildly helpful for digestion. For someone with gallstones, provoking gallbladder contraction can trigger biliary colic, and if a stone lodges in the duct the result is a genuine medical emergency.

Avoid devil's claw if you have known gallstones or biliary obstruction, or use it only with a doctor's explicit agreement. The same applies to anyone with a history of pancreatitis related to gallstones.

The Cardiac Caution — What the Animal Data Actually Show

This is the caution most often stated vaguely, so here is what the underlying research actually reported. Two studies from the same Italian group in the mid-1980s examined devil's claw's cardiovascular pharmacology, and their findings are specific enough to be useful.

In conscious rats

A dried crude methanolic extract of the secondary roots produced a significant, dose-dependent reduction in arterial blood pressure, reaching significance at higher oral doses (a dried extract dose of 400 mg/kg). Heart rate fell at the same time. Purified harpagoside alone was less active than an amount of whole extract containing the equivalent harpagoside — another reminder that harpagoside is a marker, not the sole actor.

In isolated rabbit hearts

In spontaneously beating Langendorff preparations, the extract produced a mild fall in heart rate, with a mild positive inotropic effect (stronger contraction) at lower doses and a marked negative inotropic effect (weaker contraction) at higher doses. Coronary flow fell at higher doses only. Purified harpagoside showed comparatively stronger negative chronotropic and positive inotropic effects than the extract; harpagide had a slight negative chronotropic and a considerable negative inotropic effect.

And — importantly — an antiarrhythmic effect

In both intact rats and isolated hearts, the extract was protective against experimentally induced arrhythmias: those provoked by aconitine, and particularly those provoked by calcium chloride and epinephrine–chloroform. A companion study looked at hyperkinetic ventricular arrhythmias induced by reperfusion.

How to read all that

The honest summary is not “devil's claw causes arrhythmias.” It is that devil's claw is measurably cardioactive in animals — it lowers heart rate and blood pressure, it changes contractile force in a dose-dependent and direction-changing way, and it interferes with arrhythmia generation. A substance that does all of that is a substance that can interact with drugs doing the same jobs.

The practical consequences:

• Antiarrhythmic drugs — amiodarone, flecainide, sotalol and others: treat devil's claw as a potential interaction and clear it with your cardiologist first.
• Digoxin — doubly flagged, because of the rate and contractility effects and because digoxin is a classic P-glycoprotein substrate (see below).
• Rate-control and blood-pressure drugs — beta-blockers, calcium-channel blockers, and antihypertensives generally: watch for additive bradycardia or hypotension, especially dizziness on standing.
• Existing arrhythmia or conduction disease — atrial fibrillation, heart block, a pacemaker: this is a conversation with your doctor, not a self-service decision.

Keep the evidence level in view. This is animal and isolated-organ work from the 1980s, at doses that may not correspond to a human capsule, and there is no body of human cardiac case reports to match it. It is a well-founded caution, not a documented human harm. But it is specific, it is reproducible, and it is a reason to declare the herb to a cardiologist rather than assume a supplement does not count.

Warfarin, Anticoagulants and Bleeding

A possible interaction between devil's claw and warfarin appears in essentially every serious herbal-safety reference. It rests on two things: case-level reports of altered anticoagulation or bleeding in people taking both, and pharmacological plausibility — a herb that affects drug-metabolising enzymes and transporters can shift the level of a drug with a famously narrow therapeutic window.

What does not exist is a controlled human interaction study. Nobody has given devil's claw to warfarin-stabilised volunteers and measured what happened to their INR. The evidence is therefore thin but pointed in one direction, and with warfarin, thin-but-pointed is enough.

Practical position:

• Do not add devil's claw to warfarin without telling your anticoagulation clinic. This is not a formality — it is exactly the kind of change they need to know about.
• If it is started, expect more frequent INR checks for the first several weeks, and again if you change brand or dose.
• Report unusual bruising, nosebleeds, bleeding gums, blood in urine or stool, or unusually heavy periods immediately.
• Apply the same caution, with less certainty, to direct oral anticoagulants (apixaban, rivaroxaban, edoxaban, dabigatran) — several are P-glycoprotein substrates, so the transporter data below apply. There is no INR to monitor with these, which makes an unnoticed interaction more dangerous, not less.
• Antiplatelet drugs (aspirin, clopidogrel) warrant a mention to your prescriber, though the concern is weaker.

P-Glycoprotein, CYP Enzymes and Other Medicines

The most concrete drug-interaction data on devil's claw comes from a 2009 cell study on the multidrug transporter ABCB1, better known as P-glycoprotein. P-glycoprotein is a pump in the gut wall, kidney, liver and blood–brain barrier that throws drugs back out of cells; inhibit it and blood levels of its substrates rise, induce it and they fall.

The findings, in human kidney proximal tubule cells:

• Three commercially available devil's claw preparations inhibited P-glycoprotein activity, to differing extents.
• Pure harpagoside was almost ineffective — so the effect does not track the marker compound, and one product's behaviour cannot be predicted from another's harpagoside content.
• After three days of exposure, the preparations produced a dose-dependent up-regulation of P-glycoprotein expression — the opposite direction from the acute inhibition.

That last point is the awkward one. Acute inhibition and chronic induction pointing opposite ways means the direction of any real-world interaction could change between the first week and the second month. The authors' own conclusion was that these results raise the possibility of herb–drug interactions requiring further study.

Devil's claw has also been included in screening work measuring the inhibitory potency of herbal extracts against six major cytochrome P450 enzymes. As with the transporter data, this is in vitro screening rather than a human interaction study, and it should be read as a flag rather than a quantified risk.

What to do with this. If you take a drug with a narrow therapeutic index — where a modest change in blood level matters — treat devil's claw as something to clear with a pharmacist first. That list includes digoxin, warfarin, ciclosporin and tacrolimus, several antiarrhythmics, some anticonvulsants, some HIV and hepatitis antivirals, and the direct oral anticoagulants. Pharmacists are genuinely good at this question and it costs nothing to ask.

Pregnancy, Breastfeeding and Children

Avoid devil's claw in pregnancy. Two independent reasons:

1. Devil's claw has a traditional reputation as an oxytocic — a uterine stimulant — in southern African use. Traditional reputation is not proof, but for a pregnancy exposure it is more than enough reason to abstain.
2. There is no adequate human safety data in pregnancy, and none is likely to be generated. Absence of evidence is not reassurance.

Breastfeeding: no meaningful safety data on transfer into milk or effects on an infant. Avoid.

Children and adolescents: the EMA herbal monograph restricts devil's claw to adults. There is no paediatric dosing and no paediatric safety data.

Diabetes, Blood Pressure and Surgery

• Diabetes. Devil's claw may lower blood glucose. If you take insulin or an oral hypoglycaemic, monitor more closely when starting or stopping, and know your hypoglycaemia symptoms. The effect is not large or well quantified, but additive effects are the concern.
• Blood pressure. The animal data above show dose-dependent falls in blood pressure. On top of antihypertensive medication, watch for light-headedness on standing, particularly in older adults where a fall is the real risk rather than the number itself.
• Before surgery. Stop devil's claw one to two weeks before any planned procedure, given the possible effects on bleeding, blood glucose, blood pressure and heart rate. Tell the anaesthetist and surgical team you have been taking it, even after stopping — herbal supplements are among the most under-declared things in a pre-operative assessment.
• Kidney and liver disease. No specific evidence of harm, but no adequate data either. Discuss it first.

Who Should Not Take Devil's Claw

Sustainability — the Part Nobody Puts on the Label

Almost every gram of devil's claw sold in Europe and North America was dug out of the wild. It is not meaningfully farmed at commercial scale. The plant grows in the deep Kalahari sands of Namibia, Botswana and South Africa, Namibia being the dominant exporter, and it is harvested by hand, largely by rural people in some of the most economically marginal communities in the region, including San (Khoe-San) harvesters.

That creates a genuine dilemma rather than a simple villain. Over-collection threatens the resource. But the harvest is also a rare source of cash income in areas with almost no alternatives, and it is seasonal, requiring no capital, accessible to people with no land. Any conservation measure that simply shuts the trade down transfers the cost onto the poorest people in the chain.

What actually happened at CITES

Devil's claw is often described as “CITES-protected.” That is not correct, and the real history is more interesting.

At the eleventh CITES Conference of the Parties in 2000, held in Kenya, Germany — the largest importing country — proposed listing Harpagophytum species in Appendix II, the tier that permits regulated trade with export permits. The southern African range states opposed it, on two grounds: fear that a listing would damage the livelihoods of thousands of harvesters, and the absence of solid data on population status and harvest impact. The proposal was withdrawn. Devil's claw is not CITES-listed today.

What exists instead is a patchwork:

• EU monitoring. Harpagophytum species are listed in Annex D of the EU Wildlife Trade Regulation — a monitoring annex requiring import notification so trade volumes can be tracked. It is surveillance, not restriction.
• National protection. Devil's claw is a protected species in Namibia, Botswana and South Africa, with permit systems governing harvesting and export.
• Community harvesting programmes. Namibia's Sustainably Harvested Devil's Claw initiative, running since the late 1990s, is built on the premise that harvesters who capture more of the value have a direct interest in not exhausting the resource. Organic and fair-trade-style certification schemes now cover part of the supply.

Why the harvesting technique is the whole story

Recall the botany from the Benefits hub: the medicine is the secondary storage tubers, not the primary taproot. That single fact determines whether harvesting is renewable or extractive.

• Sustainable practice: dig a trench along a lateral root, remove some of the secondary tubers, leave the primary taproot and some tubers intact, and refill the hole so the plant can regrow. A plant harvested this way can be returned to after several years.
• Destructive practice: dig out the entire plant including the taproot. Faster, higher yield today, and the plant is dead. Repeated across a heavily worked area, local populations decline.

The landmark analysis of the commercial harvest — published in 2005 under the title the devil's in the details — makes exactly this argument at scale: the sustainability of devil's claw cannot be settled by looking at export tonnages, because it depends on land tenure, harvest technique, who trains the harvesters, how the trade is structured and how much of the final price reaches the person with the digging stick. Change the details and the same tonnage is either sustainable or ruinous.

What this means for you as a buyer

You cannot verify a supply chain from a shelf. But the market responds to what customers ask about, and three questions are worth asking:

1. Where was it harvested, and under what permit? A manufacturer that knows should be able to say Namibia, Botswana or South Africa, and mention a permit or programme.
2. Is there a sustainability or fair-trade certification? Organic certification, FairWild-style schemes and named community-harvesting programmes are all meaningful signals. A vague “ethically sourced” with no scheme behind it is not.
3. Which species, and is it verified? Species identity is both a quality question and a conservation one — substitution between H. procumbens and H. zeyheri has been documented in traded material.

And one thing that helps more than any certificate: do not take devil's claw you do not need. This is a wild-dug root from a semi-desert, taken by people who need the income, for a treatment with a number-needed-to-treat somewhere around six to nine. If you have given it a fair twelve-week trial at a proper dose and nothing changed, stopping is not just good for you. It is the right call for the plant and for the people digging it.

Buying Well

Pulling the safety and sustainability threads together into one short list:

• Check the cautions above against your own medicines and conditions before you buy anything. Warfarin, arrhythmia, ulcers, gallstones and pregnancy are the five that matter most.
• Buy on stated harpagoside content, so you can reach the 50–60 mg/day studied range — the arithmetic is in the dosing article.
• Prefer a named species and a named sourcing programme.
• Tell your doctor and pharmacist you are taking it — and tell the surgical team if you are having an operation.
• Set a review date. Four weeks to check tolerance, twelve weeks to decide whether it works.

Key Research Papers

Every identifier below was verified live against NCBI E-utilities before it was written — first author, title, journal and year all had to match. Where a claim rests on case reports or regulatory documents rather than an indexed paper, a topic search is given instead of a number.

Safety and tolerability

1. Vlachojannis J, Roufogalis BD, Chrubasik S. Systematic review on the safety of Harpagophytum preparations for osteoarthritic and low back pain. Phytotherapy Research. 2008;22(2):149–152.
2. Chantre P, Cappelaere A, Leblan D, Guedon D, Vandermander J, Fournie B. Efficacy and tolerance of Harpagophytum procumbens versus diacerhein in treatment of osteoarthritis. Phytomedicine. 2000;7(3):177–183. — diarrhoea 8.1% on devil's claw versus 26.7% on diacerein.
3. Warnock M, McBean D, Suter A, Tan J, Whittaker P. Effectiveness and safety of devil's claw tablets in patients with general rheumatic disorders. Phytotherapy Research. 2007;21(12):1228–1233. — 259 patients with bloods and liver function tests.
4. Joshi K, Parrish A, Grunz-Borgmann EA, Gerkovich M, Folk WR. Toxicology studies of aqueous-alcohol extracts of Harpagophytum procumbens subsp. procumbens (Burch.) DC. ex Meisn. (Pedaliaceae). BMC Complementary Medicine and Therapies. 2020;20(1):9.
5. Denner SS. A review of the efficacy and safety of devil's claw for pain associated with degenerative musculoskeletal diseases, rheumatoid, and osteoarthritis. Holistic Nursing Practice. 2007;21(4):203–207.

Cardiovascular pharmacology — the basis of the cardiac caution

1. Circosta C, Occhiuto F, Ragusa S, Trovato A, Tumino G, Briguglio F, de Pasquale A. A drug used in traditional medicine: Harpagophytum procumbens DC. II. Cardiovascular activity. Journal of Ethnopharmacology. 1984;11(3):259–274.
2. Costa De Pasquale R, Busa G, Circosta C, et al. A drug used in traditional medicine: Harpagophytum procumbens DC. III. Effects on hyperkinetic ventricular arrhythmias by reperfusion. Journal of Ethnopharmacology. 1985;13(2):193–199.

Drug interactions — transporters and enzymes

1. Romiti N, Tramonti G, Corti A, Chieli E. Effects of devil's claw (Harpagophytum procumbens) on the multidrug transporter ABCB1/P-glycoprotein. Phytomedicine. 2009;16(12):1095–1100.
2. Unger M, Frank A. Simultaneous determination of the inhibitory potency of herbal extracts on the activity of six major cytochrome P450 enzymes using liquid chromatography/mass spectrometry and automated online extraction. Rapid Communications in Mass Spectrometry. 2004;18(19):2273–2281.
3. Unger M. Pharmacokinetic drug interactions by herbal drugs: critical evaluation and clinical relevance [in German]. Wiener Medizinische Wochenschrift. 2010;160(21–22):571–577.
4. Devil's claw and warfarin — no controlled human interaction study exists; the caution rests on case-level reports and plausibility. PubMed search.

Digestive pharmacology

1. Torres-Fuentes C, Theeuwes WF, McMullen MK, et al. Devil's claw to suppress appetite — ghrelin receptor modulation potential of a Harpagophytum procumbens root extract. PLoS One. 2014;9(7):e103118.
2. Soulimani R, Younos C, Mortier F, Derrieu C. The role of stomachal digestion on the pharmacological activity of plant extracts, using as an example extracts of Harpagophytum procumbens. Canadian Journal of Physiology and Pharmacology. 1994;72(12):1532–1536.

Sourcing, conservation and species identity

1. Stewart KM, Cole D. The commercial harvest of devil's claw (Harpagophytum spp.) in southern Africa: the devil's in the details. Journal of Ethnopharmacology. 2005;100(3):225–236.
2. Mncwangi N, Chen W, Vermaak I, Viljoen AM, Gericke N. Devil's claw — a review of the ethnobotany, phytochemistry and biological activity of Harpagophytum procumbens. Journal of Ethnopharmacology. 2012;143(3):755–771.
3. Mncwangi NP, Viljoen AM, Zhao J, Vermaak I, Chen W, Khan I. What the devil is in your phytomedicine? Exploring species substitution in Harpagophytum through chemometric modeling. Phytochemistry. 2014;106:104–115.
4. CITES CoP11 (2000) proposal to include Harpagophytum procumbens in Appendix II, and its withdrawal. CITES proposal document.

Live PubMed Searches

1. Harpagophytum safety and adverse effects
2. Harpagophytum cardiovascular effects
3. Herb–drug interactions and P-glycoprotein
4. Warfarin, herbal supplements and INR
5. Bitter herbs and gastric acid secretion
6. Devil's claw sustainable harvesting in Namibia
7. Wild-harvested medicinal plants, conservation and livelihoods
8. Herbal medicines and pre-operative discontinuation

Connections

• All Herbs
• Devil's Claw Benefits — hub
• Osteoarthritis and Joint Pain
• Low Back Pain
• Harpagoside, Dosing and Extract Types
• Devil's Claw — main topic page
• Boswellia
• Turmeric
• Willow Bark — the salicylate cautions run in parallel
• Ginger
• Orthopedics
• Osteoarthritis

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