After switching from branded to generic imatinib, many patients with gastrointestinal stromal tumours (GIST) in the Netherlands reported new adverse events.

To objectify adverse events and assess the safety of the transition to generic imatinib, we conducted this retrospective observational study.

Many events following the switch were likely mistakenly attributed to it, as imatinib-related events also occurred frequently in our reference group, without a switch.

Between branded and generic imatinib, excipients were largely similar, and there was no difference in plasma trough levels.

We hypothesize that some adverse events after switching to generic imatinib can be attributed to the nocebo effect.

Our findings support that the switch to generic imatinib among patients with GIST in the Netherlands was generally safe.