 In this open-label, single site, dose escalation study, the maximum tolerated dose MTD of guanabenz in MS patients will be determined. Patients will be screened for participation under the existing MS natural history study 89-N-0045. Sequential patient enrollment will be spaced at least 6 weeks apart. Five study drug doses will be explored: 4mg, 8mg, 16mg, 32mg and 64mg. Dose escalation will ensue if the preceding dose is tolerated, defined both by patient-reported outcomes and objective clinical and imaging assessments. Patients will be maintained on lower doses 4mg-16mg for 14 days and on higher doses 32 and 64mg for 28 days. 