Study design: A double-blind, randomized placebo-controlled multi-centre trial comparing Acetium capsules (100mg L-cysteine, twice a day) and placebo in prevention of migraine attacks during a 3-month trial period. A cohort of 200 voluntary subjects (women and men, with aural or non-aural migraine) are invited through the Finnish Migraine Association (FMA), to participate in the study. To be eligible, the subjects should: i) have the attack frequency of 2-8 times per month, ii) have had migraine for at least 1 year, iii) have the onset of their migraine before 50 years of age, iv) be between 18 and 65 years of age, and v) have a minimum of co-morbidity. Eligible patients are allowed (if they want) to continue their current migraine prophylactic medication prior to study entry. Before enrolment in the cohort, all subjects are requested to sign a written consent. The study protocol will be subjected for approval by the Regional Committee on Medical Research Ethics (HUS).