Cat’s claw – a thorny issue of a lack of research in humans
The Irish Times
Health Supplement, p. 13
8 July 2008
DOES IT WORK? Cat’s claw and arthritis
Cat’s claw is the name given to woody vines that grow in the jungles of the Amazon. Its name comes from its claw-shaped thorns. In South American folk medicine, a tea made from the bark or roots has been to control inflammation and treat arthritis. In recent years, this has led to much interest in the herb to treat inflammatory conditions like arthritis and rheumatism.
In the Amazon, about 20 different vines are known by the name cat’s claw (or its Spanish equivalent, uña de gato). Two of the most commonly used species are Uncaria tomentosa and Uncaria guianensis. The two are very difficult to distinguish from one another, except by chemical tests. In the Amazon, traditional healers use the two species interchangeably. However, Uncaria tomentosa was the first species used in dietary supplements outside the Amazon and quickly became more popular.
Evidence from studies
Both species of cat’s claw contain numerous compounds, many of which are antioxidants. Antioxidants are known to be beneficial for general health, and in particular to reduce the risk of heart disease and cancer. Diets rich in antioxidants also appear to reduce the risk of some inflammatory diseases, including arthritis.
Laboratory studies have shown that cat’s claw extracts contain several compounds that effect inflammation and immunity. Compounds from Uncaria tomentosa stimulate the human immune system, while Uncaria guianensis contains similar compounds along with ones having the opposite effects. A 2002 study showed that while both species are active as anti-inflammatory agents and antioxidants, Uncaria guianensis is more potent.
In spite of a relatively large amount of laboratory research on cat’s claw, very few studies have examined its effectiveness in humans. A small, 4-week study of Uncaria guianensis for osteoarthritis of the knee found that people had less pain with exercise, but not at rest, when compared to a placebo. Only two other studies were found where cat’s claw was given to people with osteoarthritis, but in both it was given in combination with other dietary supplements. Both found some beneficial effects, but it is impossible to separate the benefits of the different supplements from one another.
Given that very little research has been conducted in humans, little is known about the adverse effects of cat’s claw. In the few clinical trials conducted to date, headache and dizziness were reported by a small number of people. Since cat’s claw contains compounds that stimulate the immune system, it should not be taken by people with autoimmune disorders like multiple sclerosis (MS) or lupus.
Cat’s claw was also used traditionally in the Amazon as a contraceptive. Drinking a tea made from the roots for three consecutive months was said to prevent pregnancy for four years. While scientific evidence for this has not been reported, women would best avoid using cat’s claw when pregnant, breast-feeding or hoping to become pregnant.
Cat’s claw contains numerous compounds with anti-inflammatory activity. However, these have varying potency and often contradictory effects. This leads to plants with very different effects on the body. A good deal of research is under way to identify which compounds may be safely taken by humans and for which conditions.
For now, cat’s claw products are too variable to recommend for use. Shamans and folk healers in the Amazon developed ways to recognise this variability, but Western producers often ignore it. Many products do not state which of the species they contain, simply labelling them all as ‘cat’s claw.’ The little we know about the contents of cat’s claw demonstrates why detailed, accurate labels are needed on herbal remedies.