The goal of this clinical trial is to learn if ketamine works to reduce craving for opioids in adults entering methadone treatment for opioid use disorder. The main questions it aims to answer are:
* Does ketamine reduce craving for opioids in patients with opioid use disorder?
* Does ketamine reduce symptoms of opioid withdrawal such as depression, pain, and poor sleep quality?
* Do patients who take ketamine stay in methadone treatment longer, and/or have better treatment outcomes than those given the placebo?
Researchers will compare ketamine to an active placebo (a look-alike substance that contains a drug that does not do anything to help the condition it is supposed to treat but will mimic some of the side effects of ketamine) to see if ketamine works to reduce craving for opioids in adults entering methadone treatment for opioid use disorder.
Participants will:
* Be given ketamine or a placebo 4 times over a period of 2 weeks
* Visit the clinic weekly and monthly for checkups and tests for 90 days post-intake