European Journal of Clinical Pharmacology

, Volume 72, Issue 11, pp 1381–1389 | Cite as

Adherence to antidepressants among women and men described with trajectory models: a Swedish longitudinal study

  • Ann-Charlotte Mårdby
  • Linus Schiöler
  • Karolina Andersson Sundell
  • Pernilla Bjerkeli
  • Eva Lesén
  • Anna K. Jönsson
Pharmacoepidemiology and Prescription



The purpose of this study are to analyse adherence to antidepressant treatment over 2 years in Sweden among women and men who initiated treatment with citalopram and to identify groups at risk of non-adherence using trajectory models.


The study population, including individuals 18–85 years who initiated citalopram use between 1 July 2006 and 30 June 2007, was identified in the Swedish Prescribed Drug Register and followed for 2 years. Adherence was estimated with continuous measure of medication acquisition (CMA) and group-based trajectory modelling, a method which describes adherence patterns over time by estimating trajectories of adherence and the individual’s probability of belonging to a specific trajectory.


The study population included 54,248 individuals, 64 % women. Mean CMA was 52 % among women and 50 % among men (p < 0.001). Five different adherence patterns (Trajectories) were identified. Similar proportion of women and men belonged to each Trajectory. Around 29 % of the women and 27 % of the men belonged to the Trajectory which showed full adherence throughout the 2-year study period. The other four Trajectories showed adherence that declined to different degrees and at different stages in time. Having low socioeconomic status was more common among individuals in Trajectories showing declining adherence than in the adherent Trajectory.


Using trajectory modelling, five Trajectories describing different patterns of adherence to citalopram treatment over time were identified. A large proportion discontinued treatment early and having low socioeconomic status increased the risk of being non-adherent.


Medication adherence Swedish prescribed drug register Gender Antidepressants Trajectory models 



The data collection for this work has been supported by the National Corporation of Swedish Pharmacies (Apoteket AB). The Swedish Medical Products Agency provided funding for this project for author AKJ, PJ, and for statistical assistance. The county council of Östergötland provided funding for this project for author AKJ.

Contribution of authors

A-CM, AKJ, KAS, PB, and EL conceived the study question. A-CM organised the study, interpreted the results, and drafted the manuscript. AKJ processed the data, conducted statistical analyses, interpreted the results, and drafted the manuscript. LS processed the data and conducted statistical analyses. PB validated the algorithm. LS, KAS, PB, and EL contributed to the interpretation of the results and critically revised the manuscript for important intellectual content. All authors have read and approved of the final manuscript.

Compliance with ethical Standards

The study was performed in compliance with the Declaration of Helsinki from 1964 and its later amendments. The Regional Ethics Review Board in Gothenburg, Sweden, has approved the RARE-project before start, No. 284–09. With the ethics approval, the register data was retrieved from and linked together by the Statistics Sweden and Swedish National Board of Health and Welfare. The data was delivered in de-identified files with a random serial number instead of the personal identity numbers. In concordance with the ethics approval, no formal consent was obtained since the study only includes national register data. The results were analysed and reported on group level.

Competing interests

A-CM was employed by the Sahlgrenska University Hospital and University of Gothenburg when the study was conducted, and is today employed by Novo Nordisk A/S. EL is employed by Nordic Health Economics, a research and consultancy company, and has no competing interests or financial disclosures related to the current study. KAS was employed by the University of Gothenburg when the study was conducted, and is today employed by AstraZeneca AB. The authors’ work was independent from the employers. The authors have no conflict of interest to declare related to the study question or the results presented.


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Copyright information

© Springer-Verlag Berlin Heidelberg 2016

Authors and Affiliations

  • Ann-Charlotte Mårdby
    • 1
    • 2
    • 3
  • Linus Schiöler
    • 4
  • Karolina Andersson Sundell
    • 2
    • 5
  • Pernilla Bjerkeli
    • 6
    • 7
  • Eva Lesén
    • 8
  • Anna K. Jönsson
    • 9
  1. 1.Research and DevelopmentSahlgrenska University HospitalGothenburgSweden
  2. 2.Section of Epidemiology and Social Medicine, Department of Public Health and Community Medicine at Institute of MedicineUniversity of GothenburgGothenburgSweden
  3. 3.Novo Nordisk A/SMalmöSweden
  4. 4.Section of Occupational and Environmental Medicine, Department of Public Health and Community Medicine at Institute of MedicineUniversity of GothenburgGothenburgSweden
  5. 5.Medical Evidence and Observational ResearchMölndalSweden
  6. 6.Nordic School of Public HealthGothenburgSweden
  7. 7.Department for Biomedicine and Public Health ResearchUniversity of SkövdeSkövdeSweden
  8. 8.Nordic Health Economics ABGothenburgSweden
  9. 9.Department of Forensic Genetics and Forensic ToxicologyNational Board of Forensic MedicineLinköpingSweden

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