Medication overuse and subsequent medication-overuse headache (MOH) is a growing problem worldwide. Epidemiological data suggest that up to 4% of the population overuse analgesics and other drugs for the treatment of pain conditions such as migraine and that about 1% of the general population in Europe, North America, and Asia have MOH. Recent clinical studies gave further insights in clinical and pharmacological features, such as critical monthly doses and frequencies. These features seem to vary significantly and depend on the primary headache disorder and the type of drug that is overused. Along with these findings the new international classification of headache disorders has now incorporated additional criteria and new headache entities that will facilitate the diagnosis of MOH. Withdrawal therapy is the only treatment for this disorder and clear restriction of monthly doses is the central requirement for successful prevention.