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These compounds have been implicated in fatal and non\u2010fatal overdoses. This review aims to synthesise current evidence on the pharmacological effects, potency and naloxone responsiveness of new synthetic opioids, with a focus on synthetic opioids evaluated for international control since 2020. It highlights key findings that can inform our understanding of these substances and inform harm reduction strategies.<\/jats:p>\n                  <\/jats:sec>\n                  <jats:sec>\n                    <jats:title>Methods<\/jats:title>\n                    <jats:p>A narrative review was conducted using critical reviews from the World Health Organization Expert Committee on Drug Dependence and supplementary literature. Data extraction focused on pharmacological profiles, behavioural effects, potency estimates, and naloxone effectiveness.<\/jats:p>\n                  <\/jats:sec>\n                  <jats:sec>\n                    <jats:title>Results<\/jats:title>\n                    <jats:p>Thirteen synthetic opioids were examined, with potencies ranging from similar to morphine to exceeding that of fentanyl. Naloxone demonstrated efficacy in reversing overdose symptoms for most substances, although higher doses or infusions were occasionally required.<\/jats:p>\n                  <\/jats:sec>\n                  <jats:sec>\n                    <jats:title>Discussion and Conclusions<\/jats:title>\n                    <jats:p>The variability in nitazene potency and common unintended use underscores the need for widespread education, broad naloxone access and robust drug\u2010checking initiatives. Key challenges include the detection of nitazenes in polydrug contexts and their presence in substances sold as other drugs, including falsified pharmaceuticals. Emerging evidence suggests that naloxone can reverse acute poisonings with benzimidazole opioids. However, no studies have examined the effectiveness of medications for treating opioid use disorder (e.g., methadone, buprenorphine, naltrexone) in people who are physically dependent on nitazenes. Future research should address this important knowledge gap.<\/jats:p>\n                  <\/jats:sec>","DOI":"10.1111\/dar.70040","type":"journal-article","created":{"date-parts":[[2025,10,16]],"date-time":"2025-10-16T02:27:38Z","timestamp":1760581658000},"update-policy":"https:\/\/doi.org\/10.1002\/crossmark_policy","source":"Crossref","is-referenced-by-count":7,"title":["Behavioural Effects and Naloxone Effectiveness With New\u00a0Synthetic Opioids"],"prefix":"10.1111","volume":"45","author":[{"ORCID":"https:\/\/orcid.org\/0000-0001-5341-1055","authenticated-orcid":false,"given":"Suzanne","family":"Nielsen","sequence":"first","affiliation":[{"name":"Monash Addiction Research Centre, Eastern Health Clinical School Monash University  Melbourne Australia"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Jo\u00e3o Pedro","family":"Silva","sequence":"additional","affiliation":[{"name":"UCIBIO \u2010 Applied Molecular Biosciences Unit\/i4HB \u2010 Associate Laboratory Institute for Health and Bioeconomy, Laboratory of Toxicology, Department of Biological Sciences, Faculty of Pharmacy University of Porto  Porto Portugal"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-4476-2800","authenticated-orcid":false,"given":"Jermaine D.","family":"Jones","sequence":"additional","affiliation":[{"name":"Division on Substance Use Disorders Columbia University Irving Medical Center &amp; New York State Psychiatric Institute  New York USA"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-1775-1882","authenticated-orcid":false,"given":"Alex","family":"Krotulski","sequence":"additional","affiliation":[{"name":"Center for Forensic Science Research and Education, Fredric Rieders Family Foundation  Horsham USA"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Dilkushi","family":"Poovendran","sequence":"additional","affiliation":[{"name":"Department of Health Product Policies and Standards World Health Organization  Geneva Switzerland"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Deusdedit","family":"Muzangizi","sequence":"additional","affiliation":[{"name":"Department of Health Product Policies and Standards World Health Organization  Geneva Switzerland"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Gilles","family":"Forte","sequence":"additional","affiliation":[{"name":"Division of Access to Medicines and Health Products World Health Organization  Geneva Switzerland"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Jason","family":"White","sequence":"additional","affiliation":[{"name":"Clinical and Health Sciences, University of South Australia  Adelaide Australia"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Sandra D.","family":"Comer","sequence":"additional","affiliation":[{"name":"Division on Substance Use Disorders Columbia University Irving Medical Center &amp; New York State Psychiatric Institute  New York USA"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"311","published-online":{"date-parts":[[2025,10,15]]},"reference":[{"key":"e_1_2_9_2_1","doi-asserted-by":"publisher","DOI":"10.3389\/fpsyt.2017.00110"},{"key":"e_1_2_9_3_1","doi-asserted-by":"publisher","DOI":"10.1136\/ip-2023-045091"},{"key":"e_1_2_9_4_1","doi-asserted-by":"publisher","DOI":"10.1111\/add.15832"},{"key":"e_1_2_9_5_1","doi-asserted-by":"publisher","DOI":"10.1016\/j.drugpo.2023.104015"},{"key":"e_1_2_9_6_1","doi-asserted-by":"publisher","DOI":"10.1016\/j.drugpo.2022.103854"},{"key":"e_1_2_9_7_1","doi-asserted-by":"publisher","DOI":"10.1016\/j.drugalcdep.2020.108500"},{"key":"e_1_2_9_8_1","doi-asserted-by":"publisher","DOI":"10.1192\/j.eurpsy.2021.2219"},{"key":"e_1_2_9_9_1","doi-asserted-by":"publisher","DOI":"10.1080\/20961790.2018.1460063"},{"key":"e_1_2_9_10_1","doi-asserted-by":"publisher","DOI":"10.1186\/s13033-023-00601-x"},{"key":"e_1_2_9_11_1","doi-asserted-by":"publisher","DOI":"10.1021\/acschemneuro.1c00037"},{"key":"e_1_2_9_12_1","doi-asserted-by":"publisher","DOI":"10.1007\/BF01486702"},{"key":"e_1_2_9_13_1","doi-asserted-by":"publisher","DOI":"10.1007\/s00204-024-03774-7"},{"key":"e_1_2_9_14_1","doi-asserted-by":"publisher","DOI":"10.1016\/j.drugalcdep.2023.109939"},{"key":"e_1_2_9_15_1","doi-asserted-by":"publisher","DOI":"10.1124\/jpet.123.002052"},{"key":"e_1_2_9_16_1","doi-asserted-by":"publisher","DOI":"10.1097\/ALN.0000000000002184"},{"key":"e_1_2_9_17_1","doi-asserted-by":"publisher","DOI":"10.1016\/j.pharmthera.2021.107961"},{"issue":"4","key":"e_1_2_9_18_1","first-page":"293","article-title":"Subjective and Discriminative Effects of Drugs","volume":"2","author":"Preston K. 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