Cat's Claw: A Plant for Immunity and Joints, What the Research Says

Deep in the Amazon rainforest grows a climbing plant that the indigenous people of Peru call "una de gato," the cat's claw. Cat's claw (Uncaria tomentosa) is a giant woody liana that climbs high tree trunks, and its strange name comes from the pair of curved thorns, resembling cat claws, located at the base of each pair of leaves. For centuries, the plant's bark was used in the traditional medicine of Amazonian peoples for inflammation, digestive issues, and general body strengthening.

In recent decades, this plant has moved from the jungle to the shelves of health food stores worldwide, and is now marketed primarily as a supplement to strengthen the immune system and relieve joint pain. Its main active components, a group of substances called oxindole alkaloids, show anti-inflammatory and immunomodulatory activity in laboratory studies. But there is a large gap between promising activity in a test tube and clinical proof in humans, and this is precisely where caution is required. In this article, we will separate facts from promises, review the existing human evidence, and explain why cat's claw received a yellow rating from us, and for whom it may be genuinely dangerous.

What is Cat's Claw?

Cat's claw is the Hebrew name for the plant Uncaria tomentosa, one of two main species sold under the name "cat's claw" (the other is Uncaria guianensis, a relative that also grows in South America). Here is what is important to understand about it:

• It is a climbing plant from the Amazon. It is a woody liana that grows in the rainforests of Peru and other countries in the Amazon basin. Supplements primarily use the inner bark of the stem and root.
• Its active components are oxindole alkaloids. These are compounds with two main types, pentacyclic and tetracyclic, and the distinction between them has practical importance, as we will explain.
• It also contains other antioxidant components. Including polyphenols, phenolic acids, and glycosides, which contribute to the anti-inflammatory activity attributed to the plant.
• It is marketed for two main purposes. Supporting the immune system and relieving joint pain and inflammation, although, as we will see, the human evidence is limited.

A critical point to understand is the issue of "chemotypes," the different chemical varieties of the plant. Studies have found that cat's claw exists in two main types: a variety rich in pentacyclic alkaloids, considered an immune stimulant, and a variety rich in tetracyclic alkaloids, which may actually act oppositely and affect the nervous system. Commercial products may contain different mixtures of the two varieties, making it very difficult to compare studies and predict the actual effect. This is one reason for caution.

The Connection to Immunity and Joints: The Mechanism

Research interest in cat's claw centers mainly on two key activities: effects on the immune system and anti-inflammatory effects. These two mechanisms are related, and both stem primarily from the oxindole alkaloids and antioxidant components in the plant.

First mechanism, inhibition of inflammatory mediators. Laboratory studies have shown that cat's claw extracts can inhibit the production of TNF-alpha, one of the central cytokines in inflammatory processes, and also reduce the production of prostaglandin PGE2 to some extent. Inhibition of TNF-alpha is precisely the mechanism by which some modern biologic drugs for rheumatoid arthritis work, so this finding explains the interest in the plant as a means to relieve joint pain.

Second mechanism, modulation of the immune system. Studies in humans and in the lab have found that cat's claw has immune-stimulating activity: it increases the engulfment of pathogens by white blood cells (phagocytosis), increases the activity and mobility of immune cells, and affects cytokine production. This is precisely the property that explains its marketing "for strengthening immunity," but it is also precisely the property that makes it dangerous for people with autoimmune diseases, where the immune system is already attacking the body itself. Further stimulation could worsen the condition.

Third mechanism, antioxidant activity. The phenolic components in the plant neutralize free radicals and reduce oxidative stress. Chronic oxidative stress is linked to inflammation and aging processes, so this is a relevant ancillary mechanism. It is important to emphasize that most data on these three mechanisms come from laboratory and animal studies, and the leap from them to proven clinical effects in humans is far from self-evident.

Current Evidence

Study 1: Cat's Claw and Rheumatoid Arthritis, Mur et al. 2002

This is the most cited human trial in the field. In 2002, Mur and colleagues published in the Journal of Rheumatology a double-blind, placebo-controlled trial involving 40 patients with active rheumatoid arthritis, who were already receiving standard drug therapy (sulfasalazine or hydroxychloroquine). The researchers specifically used the pentacyclic chemotype of the plant.

The trial lasted 52 weeks in two phases: in the first phase (24 weeks), half the participants received cat's claw extract and half received a placebo, and in the second phase, all participants received the extract. After 24 weeks, the cat's claw group showed a 53.2% reduction in the number of painful joints, compared to only a 24.1% reduction in the placebo group (statistically significant difference, p=0.044). Side effects were rare and mild, mainly digestive discomfort and itching, and laboratory values did not change. However, it is important to remember that this is a tiny sample of only 40 people, and the plant was given as an addition to existing drug therapy, not as a replacement.

Study 2: Cat's Claw and Knee Osteoarthritis, Piscoya et al. 2001

A second trial examined the effect on osteoarthritis. In 2001, Piscoya and colleagues published in the journal Inflammation Research a trial involving 45 patients with painful knee osteoarthritis, who took 100 mg of freeze-dried cat's claw (from the species Uncaria guianensis) or a placebo for 4 weeks.

The results showed a significant reduction in pain during activity in the cat's claw group as early as one week after starting, compared to the placebo. However, for fairness: night pain and swelling did not improve significantly, and the trial was short (only 4 weeks) and small. The plant was well tolerated, with no serious side effects or changes in liver enzymes observed. The researchers attributed the effect to the plant's ability to inhibit TNF-alpha production. This is an encouraging finding, but not proof.

Study 3: Systematic Reviews and Laboratory Activity

Beyond the two small human trials, most evidence on cat's claw comes from laboratory and animal studies. A systematic review and meta-analysis published in 2024 in the journal Frontiers in Pharmacology collected studies examining the anti-inflammatory and immunomodulatory activity of plant extracts in animal models, and found consistent support for anti-inflammatory activity and effects on immune mediators.

But this is precisely the main weakness. Strong activity in a test tube and in rats does not automatically translate into a significant, safe, and measurable effect in humans. The quality human trials amount to two, both small, short, and examining different doses and preparations. This is only preliminary evidence, far from the substantiation needed to recommend the plant as a treatment.

What About Viruses, the Digestive System, and General Health?

Beyond joints and immunity, cat's claw has been marketed and examined in various other contexts, although the evidence there is even weaker. Laboratory studies have examined possible antiviral activity, effects on cancer cells, and support for healing inflammation in the digestive tract, based on its traditional use for digestive issues. Most of this data is from test tubes or animals, with no controlled clinical trials behind it to justify use.

It is important to clarify one point clearly: Cat's claw is not a medicine for viruses, does not prevent or cure cancer, and is not a substitute for medical treatment. Its marketing as a general "immune booster" for the cold season relies on a laboratory mechanism, not on proof that it reduces illness in healthy humans. The bottom line is the same across all areas: the plant is mechanistically interesting, but expectations should remain very realistic. It is an experimental supplement, not a solution.

Should You Start Taking Cat's Claw?

This is precisely why we rated cat's claw yellow. On one hand, there are encouraging preliminary findings for relieving joint pain; on the other hand, the evidence is very limited, and especially, there are real safety issues that cannot be ignored. Here are the considerations:

• The most important danger: Autoimmune diseases. Because cat's claw is an immune stimulant, it is forbidden for people with autoimmune diseases such as lupus, multiple sclerosis, or active rheumatoid arthritis without medical supervision. Further stimulation of an immune system already attacking the body could worsen the disease. This is not just a theoretical concern.
• Dangerous for organ transplant recipients and those taking immunosuppressants. A person after a transplant takes drugs that intentionally suppress immunity to prevent organ rejection. Cat's claw acts in the opposite direction and could endanger the transplant. Anyone taking immunosuppressive drugs for any other reason should also avoid it.
• Drug interactions via liver enzymes. Cat's claw may affect the CYP3A4 enzyme, responsible for breaking down a large portion of drugs. A clinical case was reported where the plant increased drug concentrations in a patient's blood. The implication: the plant could alter blood levels of many drugs, including those with a narrow therapeutic window. Anyone taking regular medications must consult a doctor or pharmacist.
• Effects on blood pressure and blood clotting. The plant may lower blood pressure and reduce clotting, so caution is especially needed when combined with blood pressure medications, blood thinners, and before surgery.
• Pregnancy and breastfeeding. There are insufficient safety data, and traditionally, the plant has even been linked to use for contraception. Pregnant or breastfeeding women should avoid it completely.

Beyond all this, one must also remember the problem of quality and consistency. Because different products contain different chemotypes and concentrations of alkaloids, it is very difficult to know exactly what you are getting. Mild side effects reported include nausea, headache, and dizziness. As always: the absence of a dramatic warning on a label does not mean the supplement is safe for everyone.

What to Take Away from the Research?

1. If you have an autoimmune disease, avoid it completely. Lupus, multiple sclerosis, rheumatoid arthritis, and other autoimmune diseases are clear contraindications. Do not be tempted by "immune booster" marketing; that is precisely what is dangerous for you.
2. Organ transplant recipients and those on immunosuppressants, do not touch it. The plant could endanger the transplant or negate the effect of the drugs.
3. If you take regular medications, consult first. Due to the effect on CYP3A4, blood clotting, and blood pressure, it is mandatory to check for interactions with a doctor or pharmacist, especially with blood thinners and blood pressure medications.
4. Do not expect miracles, and do not give up proven treatment. If you have arthritis, the evidence for cat's claw is preliminary and small. It is not a substitute for established medical treatment, and in trials, it was given as an addition to existing therapy, not as a replacement.
5. If you still try it, choose a reliable product and start with a low dose. Look for a brand that specifies the chemotype (pentacyclic) and alkaloid content, and test tolerance gradually.

For those interested in examining the plant from a reliable source, you can purchase cat's claw on iHerb and choose brands that detail the alkaloid composition. But remember: with an immune-stimulating plant, personal suitability and medical supervision are more important than the dose. To check which supplements are truly suitable for your health goals, including immune support, according to your age and condition, you can use our personal supplement checker that rates each supplement based on the quality of evidence.

The Broader Perspective

Cat's claw is an excellent example of the gap between an impressive tradition and promising laboratory activity, on one hand, and scant clinical evidence on the other. On one hand, it is a plant with a long history in Amazonian medicine, with genuine anti-inflammatory mechanisms, and with two small human trials showing some relief in joint pain. On the other hand, the body of evidence is tiny, the preparations are not standardized, and especially, there are serious safety issues that set it apart. When you add the clear danger to autoimmune patients and transplant recipients, you get a classic profile of a yellow supplement: interesting and possibly useful under very specific conditions, but requiring great caution and informed choice.

The practical lesson is twofold. First, "immune boosting" is not always a good thing. For a healthy person, it is often an empty marketing phrase, and for a person with an autoimmune disease, it can be genuinely dangerous. Stimulating the immune system is a double-edged tool, and it is not always desirable. Second, it is important to remember that a single supplement, even with an ancient tradition behind it, does not replace the fundamentals and proven medical treatment. Joint health and a balanced immune system are built primarily from diet, physical activity, maintaining a healthy weight, and sleep, and cat's claw can be, at best and with a doctor's approval, a small and non-central contributor. And that is precisely the perspective we hold here: to rate each supplement according to what the science actually shows, when it is promising, and when, as in this case, it is better to be cautious and first ask "for whom is this dangerous."

References:
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, Journal of Rheumatology, 2002;29(4):678-681
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, Inflammation Research, 2001;50(9):442-448
Anti-inflammatory and/or immunomodulatory activities of Uncaria tomentosa (cat's claw) extracts: A systematic review and meta-analysis of in vivo studies, Frontiers in Pharmacology, 2024