Ketamine for MS Fatigue

The study treatment is designed in two 28-day cycles: for each cycle, participants will receive study infusion on Day 1 and complete follow-up visits during Days 7 and 28. Participants are randomized 1:1 to receive either ketamine (active treatment) or saline solution (placebo treatment) for their first infusion. They will not be blinded to their study assignment: the study doctor will disclose their assigned treatment group. After their first infusion cycle, participents will crossover to the other treatment group. Worded differently, if a participant received ketamine during their first infusion, they will receive placebo treatment during their second infusion. Conversely, if a participant received saline treatment during their first infusion, they will receive ketamine during their second infusion.