Researchers looked at all studies that examined methamphetamine use and its impact on people who are using medications for opioid use disorder (MOUD). The analysis compared people on MOUD who used methamphetamine and those who did not. All studies showed that patients were more likely to discontinue MOUD treatment if they used methamphetamine. Those who used methamphetamine more often were more likely to discontinue MOUD treatment than those who used it less often. There are limited treatment options for individuals who use methamphetamine and opioids together, so emphasis should be placed on developing, implementing and evaluating such services.