Summary

We describe the features of nocebo, and its impact in studies of transition from the originator to the respective biosimilar in inflammatory rheumatic diseases. Investigations in healthy volunteers as well as in the neurology and anesthesiology fields demonstrated the involved cerebral areas and the neurotransmitter pathways responsible for the nocebo response. Whether these findings are applicable to patients with inflammatory rheumatic diseases remains to be demonstrated. Nocebo may account for part of the after-switching biosimilar failures. However, in the absence of validated classification or diagnostic criteria, specific neurochemical and neuroimaging studies, the lack of data on serum tumor necrosis factor and drug levels, and the disease improvement after the switching back to the originator biologic observed in some patients, the nocebo diagnosis remains the role of the individual clinician. Investigations on nocebo pathophysiology and diagnosis are required to address its impact in after-transition biosimilar studies in rheumatology.