By David Kiefer, MD
Cat’s claw, an herbal medicine usually formulated from two species of the genus Uncaria that are found primarily in Peru and Ecuador, has a rich ethno-botanical history and recent scientific investigations have examined its physiological and possible clinical effects. Marketing of cat’s claw products abounds (an internet Google search yields 279,000 hits under the name cat’s claw), though officially, consumers only spent $289,000 on cat’s claw in 2003, 13.5% less than the year before.1
History and Traditional Use
Cat’s claw, or as the Spanish call it "uña de gato," derives its name from the shape of curved thorns that protrude from the vine of plants in the genus Uncaria. One of the species, Uncaria tomentosa, is an important medicinal plant in the pharmacopoeia of the Asháninka Indians in Peru.2 U. tomentosa also is referred to as "savéntaro," or powerful plant, and as such was believed to possess good spirits that could repair disruptions in body-spirit interactions with such conditions as anxiety.2 Indeed, specialized healers in Peru boiled sliced root bark of U. tomentosa to create a bitter medicinal drink to address anxiety. It also was used for a variety of other health problems, including abscesses, asthma, cancer, fevers, urinary tract infections, rheumatism, gastric ulcers, weakness, and contraception.2,3
Most sources list another species, U. guianensis, as having the same traditional uses with minor differences such as the leaves being used to enhance the healing of wounds, and an extract used for dysentery.4
There are many stories about the discovery of cat’s claw in South America by foreign priests and ethno-botanists who described miraculous cures that then prompted the marketing and export of cat’s claw products to Europe and North America.
Botany and Pharmacology
There are 34 species in the genus Uncaria (Family Rubiaceae, a family that also includes coffee, ipecac, and quinine), 29 in southeast Asia, one in Africa, and the two from Central and South America that are relevant to cat’s claw products available today (U. tomentosa and U. guianensis). These plants generally are large woody vines (called lianas) typically found in second-growth forest types,5 and can reach several inches in diameter and 1,000 feet in height.6
U. tomentosa and U. guianensis contain a variety of compounds, including 17 different alkaloids, terpenoids (including quinovic acid glycosides), tannins, flavo-noids, and sterols.6 The primary alkaloids are oxindole and indole alkaloids, both of which exist either as a pentacyclic or tetracyclic form. The composition of these compounds varies between plants, plant parts (i.e., roots vs. leaves), young vs. mature leaves, and when the plant is harvested in different seasons.3,4,7 Also, isomerization takes place among the pentacyclic oxindole alkaloids, some of which are more stable than others, or last longer after harvesting,3 which makes the evaluation of the activity of the individual compounds (isomers) difficult.7
There may be two specific genotypes of U. tomentosa; one chemotype with pentacyclic oxindole alkaloids and the other with tetracyclic oxindole alkaloids.2 Many of the beneficial physiological effects are due to the pentacyclic oxindole alkaloids, while the tetracyclic oxindole alkaloids may act as competitive antagonists.4,7 Therefore, it is important to correctly identify the chemotype during the manufacturing process. Interestingly, though the two plant chemotypes are botanically identical, when cat’s claw is prepared by Asháninka healer-priests, they exclusively choose the pentacyclic oxindole alkaloid type by a process that is still unknown to modern researchers.2,7
Most products marketed in the United States are based on U. tomentosa due to its higher alkaloid content and, therefore, easier standardization.8
Mechanism of Action
Researchers believe that the physiological effects of U. tomentosa and U. guianensis are due to the oxindole alkaloids, especially those of the pentacyclic type.6
Oxindole alkaloids may not account for all of the physiological effects of cat’s claw. One set of in vitro and in vivo (rat) experiments on freeze-dried aqueous extracts of cat’s claw showed that U. guianensis has more potent antioxidant and anti-inflammatory effects than U. tomentosa, despite having fewer oxindole alkaloids.8 Others point out that the use of cat’s claw to treat chronic inflammation doesn’t fit with the fact that some of the oxindole alkaloids promote phagocytosis.
Other research focuses on the antioxidant and anticancer activities of cat’s claw. Aqueous and freeze-dried extracts of U. tomentosa may act to suppress TNF-alpha and NK-kappa-B,9 and C-Med-100®, an ultrafiltered water extract of inner and outer bark from U. tomentosa (standardized to with 8-10% carboxy alkyl esters, less than 0.05% oxindole alkaloids), may lead to prolonged lymphocyte survival.10 One in vitro study found that methanolic extracts of U. tomentosa had a higher antiproliferative effect on one breast cancer cell line than aqueous extracts.11
A series of the terpenoid compounds, quinovic acids, may have some interesting antiviral effects, such as against rhinoviruses or vesicular stomatitis virus as shown in in vitro studies, as well as anti-inflammatory effects.2
Only a few small clinical studies have been conducted on the use of cat’s claw. In one study, with a goal of testing the immunomodulatory effects of cat’s claw, researchers conducted a double-blind, randomized controlled trial on 40 patients with rheumatoid arthritis.12 Patients either received one 20 mg capsule three times daily of U. tomentosa root extract (14.7 mg/g pentacyclic oxindole alkaloids, and no tetracyclic oxindole alkaloids, marketed as Krallendorn® capsules) or placebo for six months. Patients were permitted to stay on their regular medication; equal numbers of patients in each group were on sulfasalazine or hydroxychloroquine, and prednisolone. The results showed that the patients in the treatment group experienced fewer painful joints than the control group, with no significant difference in the number of swollen joints or the duration of morning stiffness. The group treated with U. tomentosa did not demonstrate a change in the laboratory values tested. Despite the small size of this trial, the results indicated that U. tomentosa may have a role as an adjuvant in the treatment of rheumatoid arthritis.
Another study examined the use of a freeze-dried preparation of U. guianensis bark for osteoarthritis of the knee.13 Forty-five people were randomized to receive either 100 mg daily of the cat’s claw preparation (n = 30) or placebo (n = 15) over four weeks in a double-blind prospective trial, assessing effects on pain at rest, at night, and during exercise. The cat’s claw group had significantly less knee pain with activity, even after just one week of treatment. Furthermore, a combined extract of U. guianensis and U. tomentosa was tested using a variety of physiological assays and demonstrated antioxidant activity via free radical scavenging effects, inhibition of TNF production, and possibly cyclooxygenase-2 inhibition.
Another trial compared the response to pneumococcal vaccine in 23 Caucasian male volunteers 40-60 years old who were randomized to receive either 350 mg twice daily of a standardized extract of U. tomentosa (C-Med-100) for two months, or placebo.14 Blood tests and a physical exam were done on study participants day 0, 30, and 60; a pneumococcal vaccine (23 valent Pneumovax) was administered on day 30. Titers were drawn again at day 180. Baseline characteristics were not identical; the control group had a greater percentage of natural pneumococcal antibodies, biasing the response expected from the two groups in the initial phase of the study. Despite this, the treatment group showed no loss in immune response at the five month blood test check as compared to the control group, and there was a slight increase in percentage of lymphocytes compared to neutrophils in blood tests of the cat’s claw-treated group.
Dosages and Forms
The specific therapeutic dose of cat’s claw remains unclear. The traditional preparation involves slowly boiling the bark of the roots or stems to prepare a drinkable decoction.3 Tinctures are dosed 1 mL one to three times daily, and 500-2,000 mg of dry extracts are mixed in water one to three times daily.6 There are also standardized extracts, some of which have been used in preclinical and clinical research as mentioned above. For example, the root extract used in the rheumatoid arthritis study (Krallendorn) is free of tetracyclic oxindole alkaloids and is dosed at 20 mg three times daily. The patented extract C-Med-100 is dosed at 300 mg daily. There is also a low-molecular-weight fraction, hot-water extract from the whole plant (8% carboxyl alkyl esters) dosed at 100 mg three times daily.6
Adverse Effects, Contraindications, and Drug Interactions
The side effects reported for cat’s claw in the clinical research trials are mild; slight gastrointestinal upset, dizziness, and headache have been reported, but were not significantly different from that noted for placebo groups. If cat’s claw is ingested as a tea or crude extract, its bitterness may cause mild nausea.6
Until more information is available, most authorities recommend against using cat’s claw in autoimmune diseases due to its immunomodulating activities.6,15 Similarly, cat’s claw should be avoided in patients with pending organ transplantation or skin grafts, or during immunosuppressive therapy. Caution should be exercised in patients taking antihypertensives due to the fact that some of the phytochemicals in cat’s claw have known hypotensive activity.6,13 Due to the traditional use as a contraceptive, and because one of the alkaloids acts as a uterine stimulant (rhynchophylline), cat’s claw should be avoided during pregnancy.16 Also, until more information about the physiological effects of cat’s claw is known, such as its effects on immature immune systems, its use should be avoided during lactation and for children younger than age 3.6,7,14
There is one case report of cat’s claw use being chronologically associated with acute renal failure in a woman with systemic lupus erythematosus.17 However, there was no discussion of the correct species, the form used, the dose, or any relevant admixtures of the botanical preparation used, making it difficult to interpret what actually happened in this person’s case.
Cat’s claw is an interesting botanical medicine based on two species found in Latin America, Uncaria tomentosa and Uncaria guianensis. In vitro and in vivo animal research show that the pentacyclic oxindole alkaloids appear particularly important as immune system stimulants, and whole plant extracts act as strong antioxidants and anti-inflammatories, perhaps through their effects on TNF-alpha. Although extracts of the root and stem bark were used traditionally, some results indicate that the leaf extracts also may be effective, and U. guianensis may be the more potent plant, despite having lower levels of oxindole alkaloids.
There are a few small clinical trials of interest suggesting that cat’s claw may be useful as an adjuvant treatment for both rheumatoid arthritis (U. tomentosa) and for osteoarthritic knee pain (U. guianensis), and as a boost to the immune response after pneumococcal vaccination (U. tomentosa). Various forms of the this plant are utilized, the most effective of which is still being determined. However, it does appear that an extract free of tetracyclic oxindole alkaloids (which antagonize the effects of pentacyclic compounds) is preferable.
Several cautions for the use of cat’s claw, including treatment of hypertension, or in autoimmune disease, pregnancy, lactation, and for children younger than age 3, are based primarily on the physiological actions of its constituents or extracts, though only mild side effects have been reported in humans.
Cat’s claw (Uncaria tomentosa or Uncaria guianensis) is an herbal medicine with an interesting history of traditional use in Latin America, some recent physiological research that points to possible antioxidant, anticancer, anti-inflammatory, and immune system effects, and a few small positive clinical trials. However, there remain many aspects of this plant that need clarification, such as formulations and dose most effective for clinical use, the exact physiological effects, and its safety profile. At present there are insufficient data to provide specific recommendations regarding appropriate therapeutic use. Practitioners would do well to wait for additional research before employing cat’s claw except in unique clinical circumstances.
Dr. Kiefer recently completed a fellowship at the Program in Integrative Medicine, College of Medicine, University of Arizona, Tucson.
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12. Mur E, et al. Randomized double blind trial of an extract from the pentacyclic alkaloid-chemotype of Uncaria tomentosa for the treatment of rheumatoid arthritis. J Rheumatol 2002;29:678-681.
13. Piscoya J, et al. Efficacy and safety of freeze-dried cat’s claw in osteoarthritis of the knee: Mechanisms of action of the species Uncaria guianensis. Inflamm Res 2001;50:442-448.
14. Lamm S, et al. Persistent response to pneumococcal vaccine in individuals supplemented with a novel water soluble extract of Uncaria tomentosa, C-Med-100. Phytomedicine 2001;8:267-274.
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17. Hilepo JN, et al. Acute renal failure caused by cat’s claw’ herbal remedy in a patient with systemic lupus erythematosus. Nephron 1997;77:361.