Devil's claw for back and joint pain: Cochrane evidence, safety and cautions

Harpagophytum procumbens grows in southern Africa, and the common name refers to the hooked fruit. The dried secondary root is used. Preparations vary from capsules to liquid extracts, and they are standardised to different amounts of the marker compound harpagoside. As with many herbal products, a tablet from one maker may not be equivalent to another.

A 2014 Cochrane review looked at two trials involving 315 participants and found low-quality evidence that daily doses of devil's claw may be better than placebo for short-term improvement in low back pain, with a possible reduction in use of rescue painkillers. The authors of the broader Cochrane review of herbal medicine for low back pain also noted that trials usually lasted around three weeks and that there is no evidence yet that these substances are safe or efficacious for long-term use.

The same review noted that authors of several included trials had potential conflicts of interest, so the results should be read with caution. Evidence for osteoarthritis is mixed, with a 2008 review concluding there is insufficient reliable evidence of long-term safety or effectiveness.

For most back pain, staying active, simple analgesia and gentle exercise or physiotherapy are the recommended routes, with imaging reserved for particular cases. A supplement is something a person might trial for a few weeks alongside those measures, not instead of an assessment.

• Seek urgent help for back pain with numbness around the genitals or bottom, new difficulty passing urine, leg weakness, or loss of bowel control.

• Pain after significant injury, with fever or unexplained weight loss, also needs prompt review.

• Tell your GP before combining devil's claw with anti-inflammatory tablets.

A 2008 systematic review of 28 clinical trials concluded that adverse events during treatment were infrequent while calling for more long-term safety data. Reported effects include diarrhoea, nausea, vomiting, abdominal pain, headache, vertigo and allergic reactions such as rash, hives and face swelling. Trials in the Cochrane review noted mild, short-lived stomach or skin problems.

Devil's claw may affect heart rate and blood pressure, and may be harmful for people with heart disease or circulatory disorders. It can lower blood glucose, so people with diabetes who take insulin or tablets need to monitor more closely. People with gallstones or peptic ulcers should avoid it.

The NHS advises that anyone already on prescribed medicines check with a pharmacist before taking a herbal medicine, and it lists blood-pressure medicines, diabetes drugs and warfarin among the groups where interactions are a concern.

Herbal medicines are not recommended in pregnancy and breastfeeding, nor for children because of limited safety data. In the UK, devil's claw is available both as registered traditional herbal medicines and as food supplements. A THR registration shows that the MHRA has assessed safety, quality and the patient leaflet, while the approved use rests on tradition rather than proven effect. The MHRA has cautioned that most herbal products on the UK market are unlicensed and that quality is variable, and the NHS advises against buying unlicensed products online.