Objective The aim of this study was to investigate knowledge about medication overuse headache ( MOH ) among pharmacy staff. Background MOH is a public health problem both in S weden and in many other countries. Persons with MOH have limited contact with health care, and medications used are to large extent over‐the‐counter ( OTC ) medications. Therefore, pharmacists have an important role in, eg, advising these individuals about their medication use. Little is, however, known about the actual level of knowledge about MOH among pharmacy staff, which determines the quality of their advice to MOH sufferers. Methods A total of 326 questionnaires were distributed to 44 pharmacies in G othenburg, S weden. The questionnaire included background questions, questions about advice on headache treatment, source of knowledge about MOH , and questions on self‐perceived and actual knowledge on MOH . Results The response rate was 70%. A majority of the pharmacy staff (90.6%) considered themselves to have knowledge about MOH to some or a greater extent. Almost half had learned about MOH through their university/vocational education. Only 8.6% knew that all 5 headache medications listed in the questionnaire can cause development of MOH , but 40% responded correctly on which treatment advice one can give a person with MOH . Actual knowledge on treatment advice differed significantly between groups of self‐perceived knowledge. Conclusion The knowledge on MOH is insufficient among pharmacy staff, but with the proper knowledge, pharmacy staff is well positioned to effect both primary and secondary prevention of MOH . We suggest not only increasing educational efforts about MOH within pharmacy programs but also continuing education at the pharmacies for all staff. Further, it is also important to increase knowledge among pharmacy customers.