OBJECTIVES To assess the proportion of patients with epilepsy switching back to branded lamotrigine after generic substitution, to investigate the possible clinical consequences of generic substitution in Germany, and to compare the results with published research data. German national guidelines recommend not to switch stable epileptic patients to a generic version of the anti-epileptic drug (AED). METHODS Retrospective IMS Disease Analyzer with longitudinal data (January 2005 to July 2008) was used. An open-cohort design was used to classify patients' observation into mutually-exclusive periods of branded versus generic use of lamotrigine. Periods of generic use were further stratified into single-generic, multiple-generic use, and switchback-cohort. Published results from Québec's provincial healthcare-plan (RAMQ) from April 1998 to July 2006 were used as comparator. Patients with at least one diagnosis for epilepsy (ICD-10: G40.x) and at least one prescription of Lamotrigine (ATC-N03A0) were selected. RESULTS A total of 1,171 patients (674 female (57.5%), mean age 39.0, SD 17.4) were observed in the German data. Compared to the RAMQ database, we found a similar distribution of patients' demographics, periods of brand use and generic switching. In the switch-group, 30.3 % of patients switched back to branded lamotrigine. There was a statistically significant difference between brand and generic periods for mean (paired t-test, p<0.0001) and median (sign-test, p<0.0001) daily dose. In contrast, the group switching from branded to generic and back to branded lamotrigine showed no significant difference in the mean (p<0.4482) and median daily dose (p<0.7744). CONCLUSIONS Lamotrigine patients in Germany switching from brand to generic lamotrigine experienced similar clinical consequences of generic substitution, as reported previously, also for other AEDs. Given the same characteristics as here, results can be transferred to a different population. Therefore, we expect comparable clinical consequences and switch back patterns for topiramate generic substitution in Germany.