The moon jellyfish (Aurelia aurita) is a scyphozoan frequently maintained in public and private aquaria. Little research has been conducted to investigate the effects of various drugs, such as anesthetics, in this species. Tricaine methanesulfonate (MS-222), a common immersion anesthetic for fish and amphibians, was evaluated in a managed population of moon jellyfish. Twenty-four clinically healthy jellyfish were assigned into three groups of eight for trials of 0.3 g/L MS-222 (low concentration [LC]), 0.6 g/L MS-222 (high concentration [HC]), and a saltwater control. The goal was to evaluate the effects of MS-222 administration on moon jellyfish movement and response to stimuli. Movement and response to stimuli were measured via rocking and probe stimulus tests and observations of bell contraction quality and body tone. These tests were performed at baseline and throughout both drug exposure and recovery periods. A threshold drug effect was defined based on systematic scoring criteria. Additionally, elastomer tags were administered to four of eight animals in each MS-222 group to evaluate response to tag placement after drug exposure. Threshold drug effect was achieved in six of eight individuals in the LC group and eight of eight individuals in the HC group. The LC group had median threshold and recovery times of 12.2 and 10.1 min, respectively, while the HC group had median threshold and recovery times of 4.0 and 19.9 min, respectively. The HC group had significantly faster time to threshold drug effect (P < 0.001) and longer recovery times (P= 0.005) than the LC group. In both the LC and HC tagged group, three of four jellyfish had no reaction to tag placement. All animals recovered uneventfully, and there were no mortalities. MS-222 at 0.3 and 0.6 g/L decreased movement and response to stimuli in moon jellyfish.