Minocycline in Clinically Isolated Syndromes (CIS)

* Minocycline 100 mg bid orally compared to identical placebo * Clinically Isolated Syndrome (CIS): Patients with a first clinical demyelinating event suggestive of multiple sclerosis (At baseline participants may meet 2010 McDonald diagnostic criteria for MS, but not 2005 criteria) * Men and women, aged 18-60y, first event within the previous 180 days; brain magnetic resonance imaging (MRI) with at least two brain T2 lesions which are at least 3 mm in diameter, and at least one of which is ovoid or periventricular or infratentorial. * Up to 24 months of study drug (Up to 12 months of study drug for patients recruited after December 31, 2012) * Patients will be discontinued from the study when they convert to McDMS based on the 2005 McDonald definition. * 12 Canadian MS Clinics * A total of 154 patients will be randomized. Because 30% of screened patients with CIS who are clinically eligible are not expected to meet the MRI criteria for inclusion, up to 280 patients will be screened.