Abstract: We included 14 RCTs (2050 participants) in this review. One trial on Solidago chilensis M. (Brazilian arnica) (20 participants) found very low quality evidence of reduction in perception of pain and improved flexibility with application of Brazilian arnica-containing gel twice daily as compared to placebo gel. Capsicum frutescens cream or plaster probably produces more favourable results than placebo in people with chronic LBP (three trials, 755 participants, moderate quality evidence). Based on current evidence, it is not clear whether topical capsicum cream is more beneficial for treating people with acute LBP compared to placebo (one trial, 40 participants, low quality evidence). Another trial found equivalence of C. frutescens cream to a homeopathic ointment (one trial, 161 participants, very low quality evidence). Daily doses of Harpagophytum procumbens (devil's claw), standardized to 50 mg or 100 mg harpagoside, may be better than placebo for short-term improvements in pain and may reduce use of rescue medication (two trials, 315 participants, low quality evidence). Another H. procumbens trial demonstrated relative equivalence to 12.5 mg per day of rofecoxib (Vioxx®) but was of very low quality (one trial, 88 participants, very low quality). Daily doses of Salix alba (white willow bark), standardized to 120 mg or 240 mg salicin, are probably better than placebo for short-term improvements in pain and rescue medication (two trials, 261 participants, moderate quality evidence). An additional trial demonstrated relative equivalence to 12.5 mg per day of rofecoxib (one trial, 228 participants) but was graded as very low quality evidence. S. alba minimally affected platelet thrombosis versus a cardioprotective dose of acetylsalicylate (one trial, 51 participants). One trial (120 participants) examining Symphytum officinale L. (comfrey root extract) found low quality evidence that a Kytta-Salbe comfrey extract ointment is better than placebo ointment for short-term improvements in pain as assessed by VAS. Aromatic lavender essential oil applied by acupressure may reduce subjective pain intensity and improve lateral spine flexion and walking time compared to untreated participants (one trial, 61 participants,very low quality evidence). No significant adverse events were noted within the included trials. C. frutescens (Cayenne) reduces pain more than placebo. Although H. procumbens, S. alba, S. officinale L., S. chilensis, and lavender essential oil also seem to reduce pain more than placebo, evidence for these substances was of moderate quality at best. Additional well-designed large trials are needed to test these herbal medicines against standard treatments. In general, the completeness of reporting in these trials was poor. Trialists should refer to the CONSORT statement extension for reporting trials of herbal medicine interventions.

Plain-language summary: Researchers from the Cochrane Collaboration examined the evidence available up to August 5, 2013. Fourteen studies tested six herbal medications and included 2050 adults with non-specific acute or chronic LBP. Two oral herbal medications,Harpagophytum procumbens(devil's claw) andSalix alba(white willow bark), were compared to placebo (fake or sham pills) or to rofecoxib (Vioxx®). Three topical creams, plasters, or gels,Capsicum frutescens(cayenne),Symphytum officinaleL. (comfrey), andSolidago chilensis(Brazilian arnica), were compared to placebo creams or plasters and a homeopathic gel. One essential oil, lavender, was compared to no treatment. The average age of people included in the trials was 52 years and studies usually lasted three weeks. Devil's claw, in a standardized daily dose of 50 mg or 100 mg harpagoside, may reduce pain more than placebo; a standardized daily dose of 60 mg reduced pain about the same as a daily dose of 12.5 mg of Vioxx®. While willow bark, in a standardized daily dose of 120 mg and 240 mg of salicin reduced pain more than placebo; a standardized daily dose of 240 mg reduced pain about the same as a daily dose of 12.5 mg of Vioxx® (a non-steroidal, anti-inflammatory drug). Cayenne was tested in several forms: in plaster form, it reduced pain more than placebo and about the same as the homeopathic gel Spiroflor SLR. Two other ointment-based medications,S. officinaleandS. chilensisappeared to reduce perception of pain more than placebo creams. Lavender essential oil applied by acupressure appeared effective in reducing pain and improving flexibility compared to conventional treatment. Adverse effects were reported, but appeared to be primarily confined to mild, transient gastrointestinal complaints or skin irritations. Most included trials were at low risk of bias and the quality of the evidence was mainly very low to moderate. A moderate grade of evidence was only found forC. frutescens. Trials only tested the effects of short term use (up to six weeks). Authors of eight of the included trials had a potential conflict of interest and four other authors did not disclose conflicts of interest. Vioxx® has been withdrawn from the market because of adverse effects, so all three substances should be compared to readily-available pain medications, such as nonsteroidal anti-inflammatory drugs (NSAIDs) and acetaminophen, for relative effectiveness and safety. Low to moderate quality evidence shows that four herbal medicines may reduce pain in acute and chronic LBP in the short-term and have few side effects. There is no evidence yet that any of these substances are safe or efficacious for long-term use. Large, well-designed trials are needed to further test the efficacy of these interventions.