Aidan G Cashin, Benedict M Wand, Neil E O'Connell, Hopin Lee, Rodrigo RN Rizzo, Matthew K Bagg, Edel O'Hagan, Christopher G Maher, Andrea D Furlan, Maurits W van Tulder, James H McAuley

Pharmacological interventions are the most used treatment for low back pain (LBP). Use of evidence from systematic reviews of the effects of pharmacological interventions for LBP published in the Cochrane Library, is limited by lack of a comprehensive overview. To summarise the evidence from Cochrane Reviews of the efficacy, effectiveness, and safety of systemic pharmacological interventions for adults with non-specific LBP. The Cochrane Database of Systematic Reviews was searched from inception to 3 June 2021, to identify reviews of randomised controlled trials (RCTs) that investigated systemic pharmacological interventions for adults with non-specific LBP. Two authors independently assessed eligibility, extracted data, and assessed the quality of the reviews and certainty of the evidence using the AMSTAR 2 and GRADE tools. The review focused on placebo comparisons and the main outcomes were pain intensity, function, and safety. Seven Cochrane Reviews that included 103 studies (22,238 participants) were included. There is high confidence in the findings of five reviews, moderate confidence in one, and low confidence in the findings of another. The reviews reported data on six medicines or medicine classes: paracetamol, non-steroidal anti-inflammatory drugs (NSAIDs), muscle relaxants, benzodiazepines, opioids, and antidepressants. Three reviews included participants with acute or sub-acute LBP and five reviews included participants with chronic LBP. Acute LBP Paracetamol There was high-certainty evidence for no evidence of difference between paracetamol and placebo for reducing pain intensity (MD 0.49 on a 0 to 100 scale (higher scores indicate worse pain), 95% CI -1.99 to 2.97), reducing disability (MD 0.05 on a 0 to 24 scale (higher scores indicate worse disability), 95% CI -0.50 to 0.60), and increasing the risk of adverse events (RR 1.07, 95% CI 0.86 to 1.33). NSAIDs There was moderate-certainty evidence for a small between-group difference favouring NSAIDs compared to placebo at reducing pain intensity (MD -7.29 on a 0 to 100 scale (higher scores indicate worse pain), 95% CI -10.98 to -3.61), high-certainty evidence for a small between-group difference for reducing disability (MD -2.02 on a 0-24 scale (higher scores indicate worse disability), 95% CI -2.89 to -1.15), and very low-certainty evidence for no evidence of an increased risk of adverse events (RR 0.86, 95% CI 0. 63 to 1.18). Muscle relaxants and benzodiazepines There was moderate-certainty evidence for a small between-group difference favouring muscle relaxants compared to placebo for a higher chance of pain relief (RR 0.58, 95% CI 0.45 to 0.76), and higher chance of improving physical function (RR 0.55, 95% CI 0.40 to 0.77), and increased risk of adverse events (RR 1.50, 95% CI 1. 14 to 1.98). Opioids None of the included Cochrane Reviews aimed to identify evidence for acute LBP. Antidepressants No evidence was identified by the included reviews for acute LBP. Chronic LBP Paracetamol No evidence was identified by the included reviews for chronic LBP. NSAIDs There was low-certainty evidence for a small between-group difference favouring NSAIDs compared to placebo for reducing pain intensity (MD -6.97 on a 0 to 100 scale (higher scores indicate worse pain), 95% CI -10.74 to -3.19), reducing disability (MD -0.85 on a 0-24 scale (higher scores indicate worse disability), 95% CI -1.30 to -0.40), and no evidence of an increased risk of adverse events (RR 1.04, 95% CI -0.92 to 1.17), all at intermediate-term follow-up (> 3 months and ≤ 12 months postintervention). Muscle relaxants and benzodiazepines There was low-certainty evidence for a small between-group difference favouring benzodiazepines compared to placebo for a higher chance of pain relief (RR 0.71, 95% CI 0.54 to 0.93), and low-certainty evidence for no evidence of difference between muscle relaxants and placebo in the risk of adverse events (RR 1.02, 95% CI 0.67 to 1.57). Opioids There was high-certainty evidence for a small between-group difference favouring tapentadol compared to placebo at reducing pain intensity (MD -8.00 on a 0 to 100 scale (higher scores indicate worse pain), 95% CI -1.22 to -0.38), moderate-certainty evidence for a small between-group difference favouring strong opioids for reducing pain intensity (SMD -0.43, 95% CI -0.52 to -0.33), low-certainty evidence for a medium between-group difference favouring tramadol for reducing pain intensity (SMD -0.55, 95% CI -0.66 to -0.44) and very low-certainty evidence for a small between-group difference favouring buprenorphine for reducing pain intensity (SMD -0.41, 95% CI -0.57 to -0.26). There was moderate-certainty evidence for a small between-group difference favouring strong opioids compared to placebo for reducing disability (SMD -0.26, 95% CI -0.37 to -0.15), moderate-certainty evidence for a small between-group difference favouring tramadol for reducing disability (SMD -0.18, 95% CI -0.29 to -0.07), and low-certainty evidence for a small between-group difference favouring buprenorphine for reducing disability (SMD -0.14, 95% CI -0.53 to -0.25). There was low-certainty evidence for a small between-group difference for an increased risk of adverse events for opioids (all types) compared to placebo; nausea (RD 0.10, 95% CI 0.07 to 0.14), headaches (RD 0.03, 95% CI 0.01 to 0.05), constipation (RD 0.07, 95% CI 0.04 to 0.11), and dizziness (RD 0.08, 95% CI 0.05 to 0.11). Antidepressants There was low-certainty evidence for no evidence of difference for antidepressants (all types) compared to placebo for reducing pain intensity (SMD -0.04, 95% CI -0.25 to 0.17) and reducing disability (SMD -0.06, 95% CI -0.40 to 0.29). We found no high- or moderate-certainty evidence that any investigated pharmacological intervention provided a large or medium effect on pain intensity for acute or chronic LBP compared to placebo. For acute LBP, we found moderate-certainty evidence that NSAIDs and muscle relaxants may provide a small effect on pain, and high-certainty evidence for no evidence of difference between paracetamol and placebo. For safety, we found very low- and high-certainty evidence for no evidence of difference with NSAIDs and paracetamol compared to placebo for the risk of adverse events, and moderate-certainty evidence that muscle relaxants may increase the risk of adverse events. For chronic LBP, we found low-certainty evidence that NSAIDs and very low- to high-certainty evidence that opioids may provide a small effect on pain. For safety, we found low-certainty evidence for no evidence of difference between NSAIDs and placebo for the risk of adverse events, and low-certainty evidence that opioids may increase the risk of adverse events.