People with allergies to plants in the Rubiaceae family or any species of Uncaria may be more likely to have allergic reactions to cat's claw. A typical allergic reaction may be itching or severe rash. Allergic inflammation of the kidneys has been reported.
Side Effects and Warnings
Few side effects have been reported from using cat's claw at recommended doses. Most side effects are believed to be rare, and some side effects are theoretical and have not been reported in humans. Examples of possible side effects include stomach discomfort, nausea, diarrhea, slow heartbeats or altered rhythm of heartbeats, kidney disease, acute kidney failure, neuropathy, decreases in estrogen or progesterone levels, and an increased risk of bleeding. Because cat's claw theoretically may increase the risk of bleeding, patients may need to stop taking cat's claw before some surgeries and this needs to be discussed with a qualified healthcare provider. Caution is advised in patients with bleeding disorders or taking drugs that may increase the risk of bleeding. Dosing adjustments may be necessary.
Some natural medicine experts discourage the use of cat's claw in people with conditions affecting the immune system, such as AIDS or HIV, some types of cancer, multiple sclerosis, tuberculosis, and rheumatologic diseases (rheumatoid arthritis, lupus, etc.). However, there are no specific studies or reports in this area, and the risks of cat's claw use in people with these conditions are not clear.
Many tinctures contain high levels of alcohol and should be avoided when driving or operating heavy machinery.
Pregnancy and Breastfeeding
Cat's claw cannot be recommended during pregnancy or breastfeeding. Historically, cat's claw has been used to prevent pregnancy and to induce abortion. Women who are pregnant or wish to become pregnant should not take cat's claw. Many tinctures contain high levels of alcohol, and should be avoided during pregnancy.
Adults (18 years and older):
There is no proven effective dose for cat's claw. Capsules, extracts, tinctures, decoctions, and teas are commercially available. As a capsule, 20 milligrams to 25 grams have been used, often taken in divided does.
Cat's claw is also available in preparations for the skin, but no specific doses have been shown to be safe or effective.
The dosing and safety of cat's claw have not been studied thoroughly in children, and it is recommended that doses are discussed with the child's healthcare provider before starting therapy.
Interactions with Drugs
In theory, cat's claw may increase the risk of bleeding when taken with drugs that increase the risk of bleeding. Some examples include aspirin, anticoagulants ("blood thinners") such as warfarin (Coumadin®) or heparin, anti-platelet drugs such as clopidogrel (Plavix®), and non-steroidal anti-inflammatory drugs (NSAIDS) such as ibuprofen (Motrin®, Advil®) or naproxen (Naprosyn®, Aleve®).
In theory cat's claw may interfere with the way the body processes certain drugs using the liver's "cytochrome P450" enzyme system. As a result, the levels of these drugs may be increased in the blood, and may cause increased effects or potentially serious adverse reactions.
Because one component in cat's claw may alter the rhythm of the heart (for example, it may slow heartbeats) or lower blood pressure, cat's claw should be used cautiously by people who take drugs to treat irregular heart rhythms, such as amiodarone (Cordarone®) or digoxin (Lanoxin®), or drugs to lower blood pressure, such as verapamil (Calan®).
Because cat's claw is believed to affect the immune system, people taking immunosuppressants such as corticosteroids, drugs for rheumatologic diseases (rheumatoid arthritis, lupus, etc.), or drugs to prevent rejection of transplanted organs should consult a healthcare provider and pharmacist before using cat's claw. Examples of such drugs are azathioprine, cyclosporine, and prednisone.
Cat's claw may interact with hormonal agents, cholesterol-lowering agents, diuretics, and agents that affect the kidneys.
Although not well studied in humans, cat's claw may interact with drugs that increase sensitivity to light, analgesics, anesthetics, antibiotics, antihistamines, anti inflammatory agents, and antiviral agents. Cat's claw may also interact with drugs used to treat cancer.
Many tinctures contain high levels of alcohol, and may cause nausea or vomiting when taken with metronidazole (Flagyl®) or disulfiram (Antabuse®).
Interactions with Herbs and Supplements
Very few interactions between cat's claw and herbs or supplements have been reported. In theory, cat's claw may interfere with the way the body processes certain herbs or supplements using the liver's "cytochrome P450" enzyme system. As a result, the levels of other herbs or supplements may become too high in the blood. It may also alter the effects that other herbs or supplements possibly have on the P450 system.
It is possible that cat's claw may lower blood pressure. Additive effects may be seen with black cohosh, curcumin, or ginger for example.
Cat's claw may alter the rhythm of heartbeats. As a result, cat's claw should be used carefully if also taken with other herbs that affect the heart, such as foxglove/digitalis.
In theory cat's claw may increase the risk of bleeding when taken with herbs and supplements that are believed to increase the risk of bleeding. Multiple cases of bleeding have been reported with the use of Ginkgo biloba, and fewer cases with garlic and saw palmetto. Numerous other agents may theoretically increase the risk of bleeding, although this has not been proven in most cases.
Cat's claw may decrease estrogen levels and therefore, the effects of other agents believed to have estrogen-like properties may be altered.
Cat's claw may decrease the effectiveness of iron supplements and interact with cholesterol-lowering herbs and supplements, diuretics, mushrooms, or herbs that affect the kidneys.
Although not well studied in humans, cat's claw may interact with herbs or supplements that increase sensitivity to light. Other potential interactions are with pain-relievers, anesthetics, antibiotics, antihistamines, anti-inflammatory agents, antioxidant, and antiviral agents. Cat's claw may also interact with herbs used to treat cancer.