Cat's clawBotanical

• How strong is the evidence — the sources splitPossibly helps

  NCCIH says no conclusive evidence from human studies supports cat's claw for any health purpose, including COVID-19, and notes very few high-quality trials exist [1].
  
  RxList rates it possibly effective for osteoarthritis and rheumatoid arthritis pain [4].
  
  We are not resolving that for you. The trials underneath it are single studies of 40–45 people, which different reviewers weigh differently. ^[1]

• Knee osteoarthritisPossibly helps

  Two small double-blind trials, 45 participants each, tested 100 mg/day of freeze-dried extract for 4 weeks [2].
  
  Pain during activity and both patient- and physician-rated scores improved versus placebo (P<0.001). Pain at rest and knee swelling did not change significantly.
  
  Side effects matched placebo. A 2010 systematic review found only 4 randomized trials of cat's claw in arthritis at all, and just 2 used it alone [2]. ^[2]

• Rheumatoid arthritisPossibly helps

  A randomized double-blind trial of 40 adults with active rheumatoid arthritis added 60 mg/day of a purified Uncaria tomentosa extract to sulfasalazine or hydroxychloroquine [2].
  
  After 24 weeks the number of painful joints was 29% lower than control [7].
  
  That is one small trial, and the extract was added on top of standard medication rather than replacing it. ^[2]

• Advanced cancer — quality of life, not tumorsPossibly helps

  A phase 2 open-label study gave adults with advanced solid tumors and no remaining options 100 mg three times daily for at least 8 weeks [2].
  
  Overall quality of life, social functioning and fatigue scores improved (P=0.041, 0.034 and 0.049). No tumor response occurred [3].
  
  Memorial Sloan Kettering states cat's claw has not been shown effective for cancer or AIDS, and that human data are limited [3].
  
  A separate laboratory study found cat's claw extract stimulated survival of pediatric leukemic cells — a caution, not a benefit [3]. ^[2]

• White blood cell countsPossibly helps

  A study of 27 men taking 700 mg/day for 2 months recorded higher white blood cell counts, and a separate 4-man study found the same after 6 weeks [5].
  
  Both are tiny and uncontrolled. Nothing connects the change to any clinical outcome. ^[5]

• Whole root or vine bark, brewed as teaThe traditional preparation, taken as one cup three times daily

  Elemental content

  Unstandardized dried bark, with no declared marker compound

  Absorption

  Traditional decoction: about 1 g (a quarter teaspoon) of root bark simmered in 250 mL of water for 10–15 minutes, then strained

  Best for

  The traditional preparation, taken as one cup three times daily [7]

• Standardized extract capsulesMatching what the trials actually tested, rather than a crude bark powder

  Elemental content

  Standardized to 8–10% carboxy alkyl esters and under 0.5% oxindole alkaloids

  Absorption

  The form behind most clinical research, at 250–300 mg/day

  Best for

  Matching what the trials actually tested, rather than a crude bark powder [2]

• Purified pentacyclic-oxindole extractThe specific preparation behind the 29% painful-joint result

  Elemental content

  Purified free of tetracyclic oxindole alkaloids, which may inhibit the pentacyclic ones thought to act on immune activity

  Absorption

  Given as 20 mg three times daily in the rheumatoid arthritis trial

  Best for

  The specific preparation behind the 29% painful-joint result [7]

• TinctureA traditional liquid option. Dry standardized extract at 20–60 mg once daily is the other route

  Elemental content

  Liquid alcoholic extract with no standard marker declared

  Absorption

  Taken as a quarter to half a teaspoon (1–2 mL) up to twice daily

  Best for

  A traditional liquid option. Dry standardized extract at 20–60 mg once daily is the other route [7]

• Common and rare side effects

  Diarrhea, nausea and stomach or abdominal discomfort are the most commonly reported [2].
  
  Rare but serious: severe allergic reactions with breathing difficulty, throat swelling or hives [6]. ^[2]

• Autoimmune disease

  NCCIH warns the same immune-stimulating effect could increase symptoms of autoimmune disease [1].
  
  Its advice is to talk to a health care provider before using it at all. ^[1]

• Kidney injury

  A published case report describes acute kidney failure in a patient with systemic lupus erythematosus after taking a cat's claw herbal remedy [2].
  
  WebMD lists kidney problems among the conditions to raise with a provider before use [6]. ^[2]

• Parkinson's disease

  One case report describes Parkinson's motor symptoms worsening after a patient started oral Uncaria tomentosa, then improving again once it was stopped [2]. ^[2]

• Scheduled surgery

  Stop cat's claw at least 2 weeks before scheduled surgery [2].
  
  The stated reasons are difficulty controlling blood pressure and increased bleeding risk during the procedure [4]. ^[2]

• Liver injury signal

  A US Drug-Induced Liver Injury Network review of 2004–2013 cases found cat's claw among 32 single-ingredient supplements implicated in supplement-linked liver injury [2].
  
  That was out of 217 products with identifiable ingredients. It is a signal in a case series, not a measured rate. ^[2]

• Pregnancy and breastfeeding

  Cat's claw is not recommended in pregnancy — some studies suggest it is unsafe, and it has traditional use as an emmenagogue [2].
  
  Safety while breastfeeding has not been established [1]. ^[1]

• What is actually in the bottle

  No official standardization exists for cat's claw, preparations may mix plant sources despite 100% pure labels, and inter-batch variation has been reported [2].
  
  Compound content shifts with growing region, weather, harvest timing and processing, so switching brands or bottles can change both effects and side effects [6]. ^[2]

• The interaction sources disagree

  Healthwise, last reviewed in 2015, reports no known drug, supplement or food interactions for cat's claw [7].
  
  NCCIH, Drugs.com and RxList each describe specific concerns. The 2015 review date likely explains the gap, and we flag it rather than pick a side. ^[7]

• Anticoagulants and antiplatelet drugs

  NCCIH says cat's claw may slow blood clotting, raising bleeding risk around surgery [1].
  
  RxList rates the combination with warfarin, aspirin, clopidogrel, ibuprofen or heparin as a moderate interaction, with more bruising and bleeding [4]. ^[1]

• Blood pressure medication

  Cat's claw may add to the blood-pressure-lowering effect of antihypertensives and calcium channel blockers [4].
  
  RxList advises against combining them, on the grounds that pressure could drop too low. ^[4]

• CYP3A4 substrates

  Cat's claw may inhibit CYP3A4 liver enzymes, raising blood levels and side effects of drugs cleared by that pathway [2].
  
  Named examples: lovastatin, ketoconazole, itraconazole, fexofenadine and triazolam [4]. ^[2]

• HIV protease inhibitors

  Case reports document rising serum concentrations of atazanavir, ritonavir and saquinavir in people taking cat's claw [2].
  
  Higher blood levels mean more of those drugs' side effects, so antiretroviral therapy is a specific reason to check first [3]. ^[2]

• Immunosuppressant drugs

  Because cat's claw may stimulate the immune system, it could reduce the effectiveness of azathioprine, cyclosporine, tacrolimus or corticosteroids [4].
  
  Drugs.com states cat's claw products should be avoided by anyone on immunosuppressant therapy [2]. ^[2]

None in any ordinary sense. Cat's claw is a woody Amazon vine, and the supplement is made from the bark of its root or vine rather than an edible plant part [1].

It isn't a produce item or a culinary ingredient, so there is no food-based route to it [6].

No source addresses time of day, or whether to take it with food. That question simply hasn't been studied [7].

The one consistent signal is splitting the daily amount. WHO's monograph divides the daily total into 2–3 doses [5].

The rheumatoid arthritis regimen used 20 mg three times daily, and traditional tea is one cup three times a day [7].