Uncaria tomentosa (Cat’s Claw)

a preliminary analysis by Subhuti Dharmananda, Ph.D., Director, Institute for Traditional Medicine, Portland, Oregon

Cat’s claw, an herb found in a limited region of the upper Andes in Peru, is one of several dozen herbs being promoted these days as an effective treatment, even a potential cure, for cancer, AIDS, chronic fatigue syndrome, candida infection, arthritis, and other disorders for which modern medicine is often unsatisfactory.  The broad spectrum of action claimed for these herbs is not an impossibility, as the disorders that are said to be treated involve the immune system: there could be a central regulatory mechanism affected by a natural compound that leads to improvements for many patients with various diseases.  The suggestion that the herbs produce dramatic effects or are curative rather than merely helpful is more problematic, as clinical evaluations of several such materials have failed to confirm many of the claims that were based on individual case studies.  For example, among claimed alternative medicine cancer cures, follow-ups conducted by independent investigators have almost always led to an examination of death certificates.

One of the sad features of this on-going promotion of various remedies is that few times are they ever investigated far enough to determine actual clinical effects.  Even if not a cure, a therapy that has low toxicity, few side effects, and some ability to reduce symptoms or prolong life might be valuable, especially to patients given little hope by the current medical therapies.  Instead, it seems that importers, distributors, manufacturers, and educators—who themselves did not bother to become educated about the substances involved—like to jump the gun, make claims far in excess of what is known, relying heavily on laboratory research and a few unconfirmed and poorly delineated case studies, get a market going for the item, and then, with profits in hand, move on to the next remedy, letting the previous item fade out slowly as its enthusiasts also move on.

Cat’s claw seems exotic because it is a native Indian remedy from the mountains of Peru.  Yet, there is no evidence that it is any more valuable than less exotic items from China, India, Europe, or the U.S. which were previously considered exotic.  Apparently, the root bark of the plant has been used by the aborigines in the area where it grows for gastric distress, skin diseases, arthralgia, and cancer.  It is not clear how accurately cancer was diagnosed (in most medical traditions, cancers, abscesses, and non-malignant swellings were lumped together), nor what effect this herb had in native hands, nor whether it was only one of several remedies provided in combination to the patient.  The “claw” which characterizes this vine may have been selected by “doctrine of signatures” as something that could penetrate and puncture a lump or grab the cause of localized pain.  In China, the related plant Uncaria rhynchophylla (gouteng), is said by native healers to effectively treat headaches: the hook on the vine indicates that it can go in and grasp the pain to pull it out.  This explanation may also come after the observation of effects, as an aid to memory: Chinese research confirms that the herb can treat certain types of headache, especially that associated with hypertension.

The active components of cat’s claw are mainly alkaloids, glycosides (triterpenes and procyanidins), and tannins.  The oxindole alkaloids of the stem (including the hooks) are the same as those found in the Chinese plant that is far more intensively analyzed.  Rhynchophylline, the main alkaloid, has been made into a drug in China for treating hypertension and headache due to vascular constriction.  The alkaloids in the root bark of cats’ claw are in the same category as rhynchophylline, but are slightly differently.  The claim made by some investigators appears to be that these unique alkaloids are responsible for the ability of the plant to treat cancer and to inhibit viral infections.  Enhancement of phagocytosis in vitro was reported in 1985 by Wagner, a European researcher who has focused efforts on revealing immune-enhancing actions of natural products (his work with echinacea, eleutherococcus, and the liver-protective herb sylibum is frequently reported in the alternative medicine literature).  However, it is not clear that sufficient amounts of such alkaloids are consumed so that one would obtain this effect nor how strong the effect might be.  Based on his research experience, Wagner believes that polysaccharides, terpenoids, alkaloids, and polyphenolic compounds from plants have immunostimulating activity.

The triterpenoids of cat’s claw have been shown to have an anti-inflammatory effect.  This effect is not surprising: dozens of plants with triterpenoids have an anti-inflammatory action; triterpenoid compounds often have a steroidal structure.  Other materials have been isolated from the herb, such as oleanolic acid (which has anti-allergy actions), but the amounts are so small as to make their presence insignificant in relation to the herbal activity in clinical practice.  Clearly, one can find numerous compounds in this plant and attribute healthful activities based on in vitro tests that require large amounts of the compounds, but that doesn’t mean one is likely to obtain those effects from oral consumption of recommended amounts (e.g., 20 grams by decoction or infusion, much less by ingestion of encapsulated powders) of the crude herb.

In a patent application for use of cat’s claw alkaloids for immune-modulatory effects against cancer, other alkaloids with similar effects obtained from other plants are mentioned, such as berbamine and matrine, ingredients identified from common Chinese herbs (e.g., hu-chang and sophora) that boost certain immune responses and which can be used in the treatment of cancer (Chang and But 1987).  The question that arises is this: is it worthwhile collecting a species that has a limited growing range for which the root bark may be the key ingredient, and which is quite expensive, rather than using readily available plants that are less expensive and are already cultivated and which have far more supporting research for the intended application?  The patent application also lists more than a dozen phenols/quinones and terpenes as examples of natural substances “with stimulating effect on the immunological system.”

That aside, one can examine carefully the research to date.  In one study (Aquino, et al. 1991), anti-inflammatory compounds were isolated.  In rat paw inflammation experiments (usually used in the study of potential anti-arthritis remedies), dosages of 2 g/kg of the dried bark (corresponds to typical human dosage of 140 grams of the herb) were used, and the most active isolated fractions were able to inhibit the rat paw edema by about 40%.  Aspirin is a lot easier to use and more effective and although aspirin may cause gastric irritation, so might the isolated components of cat’s claw.  The common, cultivated Chinese herb tang-kuei, has an anti-inflammatory action that is slightly greater than that of aspirin, weight for weight. 

Antiviral activity of quinovic acid glycosides from cat’s claw were also analyzed (Aquino, Simone, and Pizza, 1989).  As the authors of the study report: “an inhibitory effect against VSV [vesicular stomatitis virus] was evident for all the nine compounds tested, although at relatively high concentrations with respect to the toxic dose....”  In other words, the antiviral activity was weak unless you approach the point where the herbal components would kill the cells as well.  Before one reaches cell killing by a compound, severe side effects would tend to be observed clinically.  The authors continue: “almost all these quinovic acid glycosides were inactive against rhinovirus type IB infection....”  These same authors mention in their introduction the antiviral action of glycyrrhizin (from licorice).  This and other components from readily-available and inexpensive herbs have been demonstrated effective in treating viral infections; for example, glycyrrhizin can cure a portion of clinical cases of chronic hepatitis B infection and it has been shown, in vitro, to inhibit HIV. 

The potential antitumor activity of cat’s claw remains pure speculation.  In a paper about the constituents of various Uncaria species in Peru, it was suggested (de Matta, et al.) that catechin in the root bark may be responsible for the effect.  Catechin is believed to be anticarcinogenic, but it is obtained from dozens of other herbs (it is often found in barks) that are much more easily obtained (rhubarb is the main source used in Chinese anticancer studies).  In a recent evaluation of antimutagenic effects (Rizzi, et al., 1992), it was speculated that cat’s claw acts as an antioxidant, thus potentially reducing the incidence of transformation to cancer cells via an oxidation reaction.  Yet, there are dozens of antioxidants already identified which have this property, many of which have useful nutritional benefits (e.g., vitamins C and E, selenium, cysteine) and which are inexpensive and readily available.  While these are thought to be useful in reducing cancer risk, their impact on existing cancers is minor.

To get around the rather poor outcomes found in laboratory experiments and the availability of alternative sources for materials for which similar claims could be made, promoters of cat’s claw resort to hyperbole.  Philip Steinberg, a nutritional consultant, proclaims it a “wondrous herb from the Peruvian Rainforest,” and refers to an article by a chiropractor, Brent Davis, who proclaims it a “world class herb.”  The patent issued more than five years ago is trotted out as primary evidence of its value.  Indeed, cat’s claw has been sold in Europe, but an analysis of the capsules of product show that it is extremely low in the supposed active components compared to reference samples from Peru (Stuppner, Sturm, and Konwalinka, 1992) so that any claims made for it are likely placebo effects.  

To promote the product, “The Cat’s Claw Quarterly” was generated.  As illustration of its irresponsible reporting, the 10 page first issue carries not one author’s name.  Keplinger, the holder of the above-mentioned patent is reported to have been treating AIDS patients in Europe.  He proclaims benefits were observed as follows: “within twenty days treatment there were positive signs in the immune system.”  Anyone working with AIDS knows that the manifestations of the disease is highly variable and that few, if any, patients stick to only one remedy at any time; besides that, there was no way to show “positive signs” in the immune system within twenty days back then (in 1987, two years before this first issue of the newsletter).  An herbal correspondence course devotes lesson 26 to cat’s claw, as part of the larger section on “killing cancer.”  All that is offered is a rambling narrative of the author’s attempt to track down information on cat’s claw (one section is headed “very little written about cat’s claw”).  As an example of successful use of the herb for cancer, here is one story he relates from Austria, where Keplinger works: Male 14-year-old [with lymph leukemia].  Chemotherapy was applied.  However, patient suffered extreme discomfort.  Cat’s claw given.  Three week’s later, blood values improved.  Patient more active.  Since the blood condition improved so much, they thought this was because of the chemotherapy.  So they increased the dosage of chemotherapy. The blood test did not reveal further pathology.  The patient is now considered a mostly healthy child.”  That certainly shows that cat’s claw is effective against cancer by the contorted reasoning methods employed by such writers.  Chemotherapy, which is effective in many cases of childhood leukemia, by this reasoning came out poorly in this report.  In a letter to Townsend Letter for Doctors (an informal and unreviewed magazine), Steinberg claims that one Peruvian physician spoke at an international congress on traditional medicine “about his and his colleagues’ successes with Uncaria tomentosa and other herbs in treating 14 types of accurately diagnosed cancer in 700 patients.”  The suggestion to be taken by the unsuspecting reader is that it was this herb that was responsible for the undefined successes.  One wonders what these physicians actually did and what was actually said about the results. 

Cat’s claw may indeed be a good remedy for gastritis (one wouldn’t be able to determine that from the current literature, however: gastritis isn’t as interesting as cancer and AIDS).  Herbal therapies for gastritis are relatively easy for native herbalists to select, because the effects are usually prompt.  There are hundreds of other gastritis remedies available; its just a matter of whether or not the gastritis sufferer will try them.  If the first they try is cat’s claw, it may well be one they can say works for them.

At this time, there is no evidence that cat’s claw has significant immunological properties. It may have such properties, but there are potential problems with promoting it for this application.  First, it appears that the tops of the plant, which mainly contain rhyncophylline in the stem and tannins in the leaves, are probably not effective for this purpose.  In China, where immune regulators are a central area of concern, Uncaria species are not counted among them.  When purchasing powdered materials, it is difficult to know if one is getting the right species (importers already caution that you buy their species of cat’s claw and not an alternative one, Uncaria guaianensis, available on the Peruvian market), much less the right plant part.  If the root bark, which may have relatively unique compounds, is to be used, then the plants must be dug up, and we have one more case of damage to the rain forest plants.  It has been suggested that the upper bark might have the same activity as the root bark, and it is possible, with vines, to collect the tops and still have the plant grow back.  However, a careful analysis of the vine bark must be made and one must be assured of getting just this part (there isn’t much bark on this plant).  But, why bother?  There are so many established immune-regulating herbs already available that putting great effort into this one seems unappealing. 

What about the current research status?  In the U.S., this is being trusted to practitioners of natural medicine untrained or poorly trained in clinical evaluations who are to report on the effects in their patients (who are almost certainly taking other remedies at the same time) under the general heading of conducting a “clinical trial.”  These practitioners will no doubt claim benefits seen in numerous patients, as they have in the past for each remedy that has been brought out for informal evaluation by practitioners untrained in research methodology.  In Austria, Dr. Keplinger is said to be using a medicine extracted from the vine along with AZT in AIDS patients.  His results (from the past eight years of experience) are being reported not in medical journals but in newspapers, such as El Comercio (Lima).  In Peru, researchers are making a sincere effort to analyze the ingredients and effects of the plant.   As reported in journals, the observed effects have been quite limited and the activities can be explained by compounds and mechanisms that do not require one use cat’s claw.   Yet, an American distributor says that “Cat’s claw promises to become a major therapeutic agent worldwide in the very near future due to its unusual and significant health-stimulating properties. “

It is quite unfortunate that the diligent efforts of Peruvian researchers are being largely ignored in favor of the outlandish claims of chiropractors, nutritional consultants, and writers of informal correspondence courses.  Desperate AIDS and cancer patients, as well as others, may be taken in by this (that is, after all, what the effort is all about), and spend their limited resources on this potentially endangered rain forest remedy when better-studied, more effective, and less expensive remedies are available to them.  This is the ongoing problem with alternative medicine: uncritical acceptance of remedies promoted by persons with limited knowledge, but strong financial interests, and unreliable enthusiasm.  If cat’s claw is a legitimate contributor to treatment of serious illnesses, then let the scientific knowledge be compiled and analyzed and then compared to what is known about other plant remedies before it is touted as the newest remedy for cancer and AIDS.


Uncaria vines are native to Japan, China, Vietnam, and the Malaysian peninsula. Among the species used in China, interchangeably, are U. rhyncophylla, U. macrophylla, U. hirsuta, U. sessifructus, U. formosana, and U. scandens.  The branch and stem are used for their nerve-inhibiting actions, associated with the alkaloid components.  They are thus applied as a sedative, anticonvulsant, hypotensive, and analgesic.   In Vietnam, U. tonkinensis is used; the bark of the vine is considered useful in lowering fever; it is said that the bark contains no alkaloids, but does contain catechin and catechutannic acid.  In Malaysia, Uncaria gambir is used.  The top of the plant is rich in tannins and is not very suitable for internal use (except temporarily to treat dysentery).  Rather, it is applied topically for its antiseptic action (attributable to tannins) and some analgesic effects (probably due to the alkaloids).  The roots are considered a remedy for intestinal inflammation, which is a common application of tannins.  Such compounds may also have a positive effect on gastritis and urethritis, conditions for which cat’s claw has been claimed to be of use.



July 1994