Written by Klara Rombauts, Italo M Cesari and the CAM-Cancer Consortium.
Updated March 9, 2017

Cat's claw (Uncaria spp)

Is it safe?

Adverse events

Three clinical trials with human volunteers showed no toxicity. The treatment of two trials consisted of a commercially available water extract of U. tomentosa called C-Med-100. In one trial the dose was 250 mg in one group and 350 mg in the other group, taken for 8 weeks; volunteers in the second trial used 2 x 350 mg daily for 2 months. In the third trial, patients with osteoarthritis of the knee were treated with freeze-dried U. guianensis 34-36. The two trials in cancer patients discussed in the ‘Does it work?’ section above also showed no toxicity measured as liver enzyme and kidney function, or any adverse events 25-26. Here an alcoholic extract was used instead of the aqueous extract in C-Med-100. It must be noted that both products contain different phytochemicals and can therefore not be compared.

Adverse effects such as diarrhoea or loose stools tend to be mild and improve with continued usage 13-15.


Cat's claw has been traditionally used for its immunostimulant and antifertility effects 14 and is contraindicated before or following any organ or bone-marrow transplant or skin graft, and also for women seeking to become pregnant. Theoretically, cat's claw can reduce platelet aggregation and have a anticoagulant effect so caution is warranted when taking anticoagulant drugs 13-15.


Owing to its purported immunostimulant effects, there might be interactions between cat’s claw and medications intended to suppress the immune system, such as cyclosporin or other medications prescribed following an organ transplant. These possible interactions still need to be proven scientifically however. Based on in vivo rat studies, cat's claw may protect against gastrointestinal damage associated with nonsteroidal anti-inflammatory drugs (NSAIDs) such as ibuprofen. Cat's claw may increase the effect of anticoagulants 13-15.

Citation Klara Rombauts, Italo M Cesari, CAM-Cancer Consortium. Cat's claw (Uncaria spp) [online document]. http://ws.cam-cancer.org/The-Summaries/Herbal-products/Cat-s-claw-Uncaria-spp. March 9, 2017.


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