- Proton pump inhibitors (PPIs) are among the most widely used drugs worldwide. However, some patients use them without a good indication.- Although PPIs are generally safe, there is an increasing number of signals of potentially serious side effects.- This article gives an overview of the incidence and prevalence of the following side effects: gastroenteritis, respiratory tract infections, hypomagnesaemia, renal function disorders, vitamin B12 and iron deficiency, dementia, osteoporosis and fractures.- It is important to prescribe a PPI only when there is a good indication for use. Patients with chronic PPI use should be checked periodically to see whether there is still an indication.- If any of the listed side effects should occur, it is advisable to consider PPI as a possible cause.