Ambulatory geriatric rehabilitation (AGR) is a prevention program for multimorbid patients with the contractual agreement to prevent the need for care and hospital admissions and to promote self-sufficiency. It provides an opportunity to reduce the prevalence of polypharmacy and to discontinue potentially inadequate medication (PIM).The study investigated the effect of AGR on the number of drugs and PIM.The observational longitudinal study was based on claims data from the statutory health insurance AOK Nordost. A comparison of the prescribed drugs with the PRISCUS list was performed. The study investigated the effect of AGR on the number of drugs prescribed and PIM in the period of two quarterly periods before and two quarterly periods after AGR. The numbers of prescribed statins, opioids, antidementia drugs, proton pump inhibitors and antidepressants were assessed and grouped into further prescriptions, new prescriptions and discontinued drug prescriptions.Out of 699 participants 682 (73% women, mean age 79 years, SD ± 5 years) were analyzed. The number of substances and PIM remained at the same levels after AGR. Psycholeptic, antiphlogistic and psychoanaleptic drugs were the most frequently prescribed PIM. The majority of statins, opioids, antidementia drugs, proton pump inhibitors and antidepressants were prescribed further. Antidementia drugs were the medication with the most newly started prescriptions.The AGR has no influence on the number of prescribed drugs and PIM. A structured drug review and a conversation with the general practitioner should be strengthened to improve drug safety and reduce polypharmacy as well as undertreatment.