Background Automatic substitution of biological medicines was introduced in Finnish community pharmacies in 2024, including glargine insulins in 2025. Patient views on this policy have mainly been studied with other patients than people with diabetes (PwD). Unlike other biological medicines, insulin has a narrow therapeutic window, carries risk of hypoglycemia and hyperglycemia, and requires patient-directed dose adjustments. Therefore, it is essential to explore the views of PwD regarding automatic substitution.

Objectives To investigate the concerns of insulin-treated PwD regarding the automatic substitution of insulins, their knowledge and information needs related to biological medicines, biosimilars, and automatic substitution, and the factors associated with this knowledge.

Methods An electronic survey was conducted in May 2024. Chi-squared test and binary logistic regression were used to examine the association between participant characteristics and outcome variables.

Results Among the 459 participants, 62% expressed concerns about whether the substituted insulin would be as good as the insulin previously used and about the expertise of pharmacists (47%) and physicians (46%). Awareness of biological medicines (67%) exceeded awareness of automatic substitution (45%) and biosimilars (38%), although 63% correctly identified the definition of a biosimilar. Inferior knowledge was associated with higher HbA1c, fewer comorbidities, shorter long-acting insulin use, male gender, age over 70, and use of long-acting insulin as part of multiple daily injections. Over half (55%) reported needing more information.

Conclusions Awareness of biosimilars and automatic substitution of biological medicines was limited among PwD. These findings underscore the importance of targeted communication and education to ensure medically safe substitutions.