| Level I | Good quality evidence |
Systematic review of RCTs with consistent findings High quality individual RCT |
| Level II |
Limited quality patient orientated evidence |
Systematic review of lower quality studies or studies with inconsistent findings Low quality clinical trial Cohort studies Case-control studies |
| Level III | Other |
Consensus guidelines, extrapolations from bench research, usual practice, opinion, disease-oriented evidence (intermediate or physiologic outcomes only), or case series |
[4] Tramadol, oral: Dowell D, Haegerich TM, Chou R. CDC Guideline for Prescribing Opioids for Chronic Pain--United States, 2016. JAMA. 2016 Apr 19;315(15):1624-45. https://www.ncbi.nlm.nih.gov/pubmed/26977696
Tramadol, oral: Ortho-Mcneil Pharmaceutical, Inc. The U.S. Food and Drug Administration approved drug label for tramadol tablets, 2008. https://www.accessdata.fda.gov/drugsatfda_docs/label/2009/020281s032s033lbl.pdf
Tramadol, oral: The Royal College of Anaesthetists. Opioid Aware Resource, 2019. [Accessed August 2019]. https://www.rcoa.ac.uk/faculty-of-pain-medicine/opioids-aware