Objectives: Depression affects an estimated one in 15 adults (6.7%) in any year. Approximately 50% of primary care patients discontinue antidepressant therapy within six months of initiation. The study objective was to determine the extent and reasons for non-adherence with antidepressants in the United States (US) and European Union (EU).

Methods: Data from the National Health and Wellness Study (NHWS), a self-administered, internet-based cross-sectional survey of US adults in 2019 and 5 EU countries (France, Germany, UK, Italy, and Spain) in 2020 was included. NHWS participants who self-reported taking daily prescription medication(s) to treat depression responded to the 19 reasons for non-adherence and one global item in the Medication Adherence Reasons Scale (MAR-Scale). MAR-Scale measures non-adherence “in the past 7 days”, on an 8-point scale ranging from 0 days to 7 days. Frequencies were used to identify the reasons for non-adherence.

Results: NHWS data had 4230 patients from the EU and 7506 patients from the US that reported taking a daily antidepressant. Based on the MAR-Scale, 46.10% of patients reported non-adherence to at least one reason in the EU, and 42.86% in the US. The most common reason for non-adherence in the EU was concern about long-term effects (23.92%) and possible side effects from the medicine (20.40%). In the US, though simple forgetfulness (20.86%) was the major reported reason for non-adherence, patients reported the lowest mean number of days (2.15 days/a week) missing medication for that reason. Non-adherence lasted longer due to lack of beliefs in needing medicines anymore, 4.06 days/a week in the US and 3.32 days/a week in the EU.

Conclusion: With antidepressants, further interventions are needed to educate the patients about the need for the medicines and to lessen their concerns about long-term effects and possible side effects from the medicines.