8 randomized controlled trials were included in this meta-analysis comparing multimodal cocktail injections for use in local infiltration analgesia containing morphine vs. cocktails injections not containing morphine in patients undergoing total knee arthroplasties. Outcomes of interest included pain scores at rest and during motion, post-operative opioid consumption, range of motion, Western Ontario and McMaster University (WOMAC) osteoarthritis index, and the incidence of nausea and vomiting. Results of the meta-analysis found no significant differences between the morphine and no morphine groups in pooled pain at rest and during motion, range of motion, WOMAC scores or the odds of nausea and vomiting. Pooled results for post-operative opioid consumption was, however, significantly lower in the morphine group compared to the control group.