A systematic review with mixed treatment comparisons meta analysis of anti-depressant treatment for adults with chronic pain

Abstract

Background: chronic pain is common and costly. Antidepressants are prescribed to reduce pain. However, there has not been a network meta-analysis examining all antidepressants across all chronic pain conditions, so effectiveness and safety for most antidepressant for pain conditions remain unknown.

Objective: to assess the efficacy and safety of antidepressants for chronic pain (except headache) in adults. Our primary outcomes were substantial (50%) pain relief, pain intensity, mood, and adverse events. Our secondary outcomes were moderate pain relief (30%), physical function, sleep, quality of life, patient global impression of change (PGIC), serious adverse events, and withdrawal.

Design: this was a systematic review with a network meta analysis. We searched CENTRAL, MEDLINE, Embase, CINAHL, LILACS, AMED and PsycINFO databases for RCTs of antidepressants for chronic pain conditions up until 4th January 2022. The review was registered in PROSPERO, (CRD42020171855), and the protocol was published in the Cochrane Library (doi: 10.1002/14651858.CD014682).

Setting: we analysed trials from all settings.

Participants: we included trials in which participants had chronic pain, defined as longer than 3 months, from any condition excluding headache.

Interventions: we included all antidepressants.

Main outcome measures: our primary outcome was substantial pain relief, defined as a reduction greater than 50%. We also measured pain intensity, mood, and adverse events, Secondary measures included moderate pain relief (above 30% reduction), physical function, sleep, quality of life, global Impression of change, serious adverse events, and withdrawal from trial.

Results: we identified 176 studies with a total of 28,664 participants. Most studies were placebo-controlled (83), and parallel armed (141). The most common pain conditions examined were fibromyalgia (59 studies); neuropathic pain (49 studies) and musculoskeletal pain (40 studies). The average length of RCTs was 10 weeks. Most studies measured short-term outcomes only and excluded people with low mood and other mental health conditions.

Across efficacy outcomes, duloxetine was consistently the highest ranked antidepressant with moderate to high certainty evidence. Standard dose was equally efficacious as high dose for the majority of outcomes. Milnacipran was often ranked as the next most efficacious antidepressant, although the certainty of evidence was lower than that of duloxetine. There was insufficient evidence to draw robust conclusions for the efficacy and safety of any other antidepressant for chronic pain.

Limitations: the evidence for anti-depressants other than duloxetine is poor. For duloxetine, it is not clear whether the effect applies to groups with both pain and low mood, since these groups were excluded from trials. There is also insufficient evidence on long term outcomes and on adverse effects.

Conclusions: there is only reliable evidence for duloxetine in the treatment of chronic pain. Duloxetine was moderately efficacious across all outcomes at standard dose. There is also promising evidence for milnacipran, although further high-quality research is needed to be confident in these conclusions. Data for all other antidepressants was low certainty. However the findings should not be read as an encouragement to prescribe antidepressant where other non-pharmacological intervention could be equally effective, especially in the absence of good evidence on side effects and safety.

Future work: there is a need for large, methodologically-sound trials testing the effectiveness of anti-depressants for chronic pain. These trials should examine long term outcomes (>6 months), and include people with low mood. There should also be better reporting of adverse events, tolerance of drugs, and long-term compliance.

Role of the funder: this project was funded by the National Institute for Health Research (NIHR) HTA programme, (NIHR128782) and has been published in the Cochrane Database of Systematic Reviews; Vol. 5, 2023. The funder of the study had no role in study design, data collection, data analysis, data interpretation, or writing of the report.

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Identifiers

ORCID for Hollie Birkinshaw: orcid.org/0000-0003-0853-2995

ORCID for Tamar Pincus: orcid.org/0000-0002-3172-5624

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