Opioid antagonists are associated with a reduction in the symptoms of schizophrenia: a meta-analysis of controlled trials

Current treatments for the symptoms of schizophrenia are only effective for positive symptoms in some individuals, and have considerable side effects that impact compliance. Thus, there is a need to investigate the efficacy of other compounds in treating both positive and negative symptoms. We conducted a meta-analysis of English language placebo-controlled clinical trials of naloxone, naltrexone, nalmefene, and buprenorphine in patients with schizophrenia to determine whether opioid antagonists have therapeutic efficacy on positive, negative, total, or general symptoms. We searched online databases Ovid Medline and PsychINFO, PubMed, EMBASE, Scopus, Cochrane library/CENTRAL, Web of Science, and Google Scholar from 1970 through February 2019. Following PRISMA guidelines, Hedges g was calculated for each study. Primary study outcomes were the within-subject change on any symptom assessment scale for positive, negative, total, or general symptoms of schizophrenia between active drug and placebo conditions. Thirty studies were included with 434 total patients. We found a significant effect of all drugs on all scales combined with both a standard random effects model: (g = 0.26; P = 0.02; k = 22; CI = 0.03–0.49) and a more inclusive bootstrap model: (g = 0.26; P = 0.0002; k = 30; CI = 0.11–0.51) and a significant effect on total scales with the bootstrap model (g = 0.25288; P = 0.015; k = 19; CI = 0.04–0.35). We also observed a significant effect of all drugs on all positive scales combined with both the random effects (g = 0.33; P = 0.015; k = 17; CI = 0.07–0.60) and bootstrap models (g = 0.32; P < 0.0001; k = 21; CI = 0.13–1.38). This evidence provides support for further testing in randomized clinical trials of a new class of non-D2-receptor drugs, based on opioid mechanisms, for the treatment of positive and negative symptoms of schizophrenia.