Headache and medication overuse: are clinical case series appropriate to reveal differential risks of different medications?

IMPORTANCE OF THE FIELD: The question of whether different migraine and headache medications show a differential risk of medication overuse headache (MOH) induction has been discussed extensively but has not been definitively answered to date. AREAS COVERED IN THIS REVIEW: Clinical case series of interest that include statements on a differential risk of MOH development due to the use of different headache medications are identified by systematic literature research and analyzed. WHAT THE READER WILL GAIN: In the present work, an expert evaluation is made of the existing evidence for different risks of different headache and migraine medications with regard to MOH occurrence, as has been claimed in various publications. TAKE HOME MESSAGE: Despite several different attempts to obtain direct or indirect answers from clinical case series, the fact is that due to the intrinsic selection bias, confounding and other limitations inherent to clinical case series, they are not suitable to answer this question reliably. Thus, the repeated claims of a differential risk of different drugs and drug groups are simply not scientifically sound.