A reader pointed out that I have not mentioned this in any of the 800 posts to date. It is a good question!
My process is always to go to sources not dependent on one individual’s experience
Common Names: cat’s claw, uña de gato, پنجه گربه in Persian, and مخلب القط in Arabic.
PubMed and Google Scholar
- On PubMed
- “Uncaria tomentosa microbiome” – Zero hits
Uncaria tomentosa – 204 hits
- “Although there are no randomized controlled trials or published human outcome studies, some conditions reportedly improved by U. tomentosa include osteoarthritis, rheumatoid arthritis, prostatitis, viral illnesses and cancer (acting as a non-specific immunomodulantign agent) ” 
“Uncaria tomentosa bacteria” – 16 hits
- “antibacterial effect of 2% CC gel against E. faecalis in infected dentin” 
- “U tomentoa gel had the same effect as 2% miconazole gel. U tomentosa gel is an effective topical adjuvant treatment for denture stomatitis.” 
- “2% chlorhexidine (CHX) +cat’s claw (CC) against the tested microbial strains ranged from 21.7 to 33.5 mm. This was the most effective substance against E. faecalis and C. albicans, followed by CHX and CC. Against S. aureus, CHX+CC, CHX, and CC showed similar antimicrobial activity (P > 0.05). ” [2010 ] CC was the least effective of the combinations tested.
- “Three percent Uncaria tomentosa inhibited 8% of Enterobacteriaceae isolates, 52% of Streptococcus mutans and 96% of Staphylococcus spp. ” 
- “Nine ethanol extracts of Brunfelsia grandiflora (Solanaceae), Caesalpinia spinosa (Caesalpiniaceae), Dracontium loretense (Araceae), Equisetum giganteum (Equisetaceae), Maytenus macrocarpa (Celastraceae), Phyllanthus amarus (Euphorbiaceae), Piper aduncum (Piperaceae), Terminalia catappa (Combretaceae), and Uncaria tomentosa (Rubiaceae), medicinal plants traditionally used in Calleria District for treating conditions likely to be associated with microorganisms, were screened for antimicrobial activity against nine bacterial strains using the broth microdilution method.”  Uncaria tomentosa was among the least effective.
- From Google Scholar
- “This small preliminary study demonstrates relative safety and modest benefit to the tender joint count of a highly purified extract from the pentacyclic chemotype of UT in patients with active RA taking sulfasalazine or hydroxychloroquine.” 
Cat’s claw is a poor financial choice. While it shows some benefits for dental issues, despite it’s long usage — there is a very significant absence of human studies showing significant benefit when taken alone. It appears to have “modest” benefit when used with antibiotics.
This  articles cites all of the reasonable studies. There is no evidence supporting it’s use in CFS, FM or IBS. The absence of published studies for a common recommendation in alternative medicine hints that there may have been studies with no positive results.