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Biosimilar medications are increasingly available across neurological diseases, alongside widespread use in cancer and systemic inflammatory disorders. Biosimilars are a version of an approved biological medicinal product, licensed on the basis of equivalence in terms of target molecule engagement, pharmacokinetic properties and clinical efficacy.1 While generic medications are identical to originator products, biological medications, such as monoclonal antibodies, are made within living cells and so cannot be copied exactly. The lower price point of biosimilar medications potentially enables wider access to high-cost therapies in healthcare systems, as has happened with monoclonal antibodies across rheumatological diseases over the past decade. In common with many phase 3 clinical trials, biosimilar trials enrol a relatively small number of treatment-naïve participants with the aim of reaching statistically informed non-inferiority endpoints. The statistical design of non-inferiority trials differs from superiority trials (with which clinicians are often more familiar), and close attention needs to be paid to margins used to define equivalence. Further, within the relatively short duration of clinical trials, only a few drug batches are used, limiting assessment of batch effects. The treatment journey and comorbidity profile of trial participants may not reflect the full diversity of patients within real world clinical practice.