Forty patients scheduled to undergo an arthroscopic anterior cruciate ligament (ACL) reconstruction surgery were randomized to receive intra-articular morphine (n=20) or intra-articular saline (n=20) injection after completion of the procedure. The primary outcome of interest was pain evaluated using a Visual Analogue Scale (VAS), measured at 6, 12, 18, and 24 hours post-spinal block anaesthesia. Additional outcomes measured included the time to first analgesic request, total morphine consumption, and the incidence of complications (i.e. nausea, vomiting, sedation, pruritus, and urinary retention). All outcomes were not statistically significantly different between the morphine and saline group (p>0.05 for all). No adverse events or complications were observed.