Introduction: The drop-out rate among patients receiving preventive treatment for migraine is higher than 30%. This situation is not very widely known and the risk factors that lead patients to drop out from treatment have yet to be identified.

Aim: To evaluate some of the factors that can predispose patients to drop out of preventive treatment.

Patients and methods: We conducted a prospective study of patients suffering from migraine who required preventive treatment for the first time with one of what are considered the top three first-choice drugs, i.e. a beta-blocker (nadolol), a neuromodulator (topiramate) or a calcium antagonist (flunarizine). Two groups were established according to whether patients dropped out of treatment or not. Different demographic and clinical variables were analysed and compared in the two groups.

Results: Of 800 patients with migraine who required preventive treatment for the first time, the drop-out rate was 19.7%. In the drop-out group, the variables 'age', 'number of seizures', 'number of seizures prior to preventive treatment' and 'side effects' showed significant differences with those from the group of patients who did not drop out of preventive treatment.

Conclusions: The drug used as preventive treatment, the side effects, a younger age and a lower number of seizures before starting the preventive treatment favoured higher drop-out rates. Whether the migraine was episodic or chronic, the presence of medication abuse and the drugs used to treat the seizures were not related with dropping out of preventive treatment.