Pilot Trial of Domperidone in Relapsing-Remitting Multiple Sclerosis (RRMS)

Primary Objectives: * To demonstrate that the investigators can recruit DMT treated RRMS patients who have breakthrough enhancing lesions identified on clinically indicated monitoring brain MRI scans and measure lesion repair over 32 weeks. * To obtain estimates of the magnitude and variability of lesion repair in DMT treated RRMS patients who are taking add-on domperidone, or no add-on treatment. The investigators will evaluate three MRI measures \[texture analysis, diffusion tensor imaging (DTI), and magnetization transfer imaging (MTI)\] for their ability to measure repair within acute enhancing lesions in RRMS. They will also evaluate repair at 16 and 32 weeks. These outcomes will aid in the development of future trials. No therapies have yet been shown to improve lesion repair, and there is no accepted trial model to evaluate lesion repair in humans. Therefore, the investigators anticipate that the data from this trial will inform the design of future phase 2 trials of therapies to promote lesion repair in MS. Secondary Objectives: * To determine the safety and tolerability of domperidone in RRMS * To determine serum prolactin levels during dosing with domperidone 10mg tid in this population * To explore metabolomic profiling during lesion repair. * To explore the impact of the following variables on lesion repair: prolactin level at 6 weeks, concurrent use of each type of DMT, Vitamin D and B12 levels at baseline, patient clinical characteristics (MS duration, EDSS), imaging characteristics (T2 lesion volume, enhancing lesion volume), patient demographics and behaviours (age, sex, smoking status).