PLOS One published an Expression of Concern on August 27, 2026 regarding a previously published cross-sectional study titled "Determinants of medication adherence among older adults with type 2 diabetes using the health action process approach: A cross-sectional study" (Mohammadi S et al., PLoS One 2025;20(9):e0332235). The concern relates specifically to the study's use of the Morisky Medication Adherence Scale-8 (MMAS-8) as the instrument for classifying adherence.
The Expression of Concern is limited to issues associated with the MMAS-8 instrument and its underlying validation literature; no additional editorial findings about other aspects of the 2025 study were reported in the notice.
After the 2025 article was published, attention was drawn to the MMAS-8 and to a 2008 validation paper by Morisky et al. (Predictive validity of a medication adherence measure in an outpatient setting) that had been cited in the study. The 2008 paper was subsequently retracted (retraction statement published in 2023) because of concerns about the reported sensitivity and specificity values.
The PLOS One Editors stated that these historical concerns about the original MMAS-8 validation prompted them to notify readers that adherence classifications in the 2025 article derived from the MMAS-8 should be interpreted with caution. The editors did not report further analysis or corrections to the 2025 article in the Expression of Concern beyond advising caution.
The corresponding author of the 2025 study informed the editors that the team used the validated Persian version of the MMAS-8 rather than relying directly on the now-retracted 2008 paper. The Persian version cited by the authors is a 2015 validation (Moharamzad Y et al., Validation of the Persian Version of the 8-Item Morisky Medication Adherence Scale (MMAS-8) in Iranian Hypertensive Patients, Glob J Health Sci. 2015;7(4):173–83). That Persian validation independently reports sensitivity and specificity values.
The corresponding author also stated that the 2025 article did not assess or depend on the sensitivity, specificity, predictive validity, or screening accuracy figures reported in the retracted 2008 MMAS-8 paper. According to the author's statement, the study used the Persian MMAS-8 instrument as validated in the independent 2015 work.
Given the sequence of events—the retraction of the 2008 MMAS-8 validation paper and the authors' reliance on a separate Persian validation—the PLOS One Editors issued an Expression of Concern to inform readers of the instrument-related issue. The editors explicitly advise that findings in the 2025 study that are based on MMAS-8 adherence classifications should be interpreted with caution.
The notice does not report additional editorial steps such as correction or retraction of the 2025 article, nor does it report changes to the study's data or analyses. The Expression of Concern functions as an alert about the provenance and validation history of the adherence measure used in the study.
The Expression of Concern cites specific works and provides provenance for the statements in the notice. Key references named in the editorial notice include:
Mohammadi S, Khorami B, Seyedtabib M, Najafpour Z. Determinants of medication adherence among older adults with type 2 diabetes using the health action process approach: A cross-sectional study. PLoS One. 2025;20(9):e0332235. (the study subject to this Expression of Concern)
Morisky DE, Ang A, Krousel-Wood M, Ward HJ. Retracted: Predictive validity of a medication adherence measure in an outpatient setting. J Clin Hypertens (Greenwich). 2008;10(5):348–54. (the original MMAS-8 validation later retracted)
Retraction statement: Predictive validity of a medication adherence measure in an outpatient setting. J Clin Hypertens. 2023;25:889–889. (retraction notice for the 2008 paper)
Moharamzad Y, Saadat H, Nakhjavan Shahraki B, Rai A, Saadat Z, Aerab-Sheibani H, et al. Validation of the Persian Version of the 8-Item Morisky Medication Adherence Scale (MMAS-8) in Iranian Hypertensive Patients. Glob J Health Sci. 2015;7(4):173–83. (the Persian MMAS-8 validation cited by the 2025 study's corresponding author)
The PLOS One Editors’ Expression of Concern itself is published as: The PLOS One Editors (2026) Expression of Concern: Determinants of medication adherence among older adults with type 2 diabetes using the health action process approach: A cross-sectional study. PLoS One 21(8): e0357069. https://doi.org/10.1371/journal.pone.0357069
Notes on interpretation
This rewritten summary reflects only the information reported in the PLOS One Expression of Concern. No additional methodological details, data changes, or outcomes were reported in the notice beyond the instrument-related concern and the authors’ response.
Readers and clinicians using the 2025 article's findings should take into account the editors' recommendation to interpret MMAS-8-based adherence classifications with caution, particularly given the documented retraction of the original MMAS-8 validation paper and the complex validation history of translated versions.