Journal of Affective Disorders
Volume 117, Issue 3 , Pages 162-167, October 2009

Association between consistent purchase of anticonvulsants or lithium and suicide risk: A longitudinal cohort study from Denmark, 1995–2001

  • Eric G. Smith

      Affiliations

    • Center for Psychopharmacologic Research and Treatment, Department of Psychiatry, University of Massachusetts Medical School, 361 Plantation Street, Worcester, MA 01605, USA
    • Corresponding Author InformationCorresponding author. Tel.: +1 781 687 2766; fax: +1 781 687 3106.
    • ,
  • Lars Søndergård

      Affiliations

    • Department of Psychiatry, University Hospital of Copenhagen, Rigshospitalet, Copenhagen, Denmark
    • ,
  • Ana Garcia Lopez

      Affiliations

    • Department of Biostatistics, University of Copenhagen, Copenhagen, Denmark
    • ,
  • Per Kragh Andersen

      Affiliations

    • Department of Biostatistics, University of Copenhagen, Copenhagen, Denmark
    • ,
  • Lars Vedel Kessing

      Affiliations

    • Department of Psychiatry, University Hospital of Copenhagen, Rigshospitalet, Copenhagen, Denmark

Received 14 August 2008; received in revised form 10 January 2009; accepted 14 January 2009.

Abstract 

Background

Prior studies suggest anticonvulsants purchasers may be at greater risk of suicide than lithium purchasers.

Methods

Longitudinal, retrospective cohort study of all individuals in Denmark purchasing anticonvulsants (valproic acid, carbamazepine, oxcarbazepine or lamotrigine) (n=9952) or lithium (n=6693) from 1995–2001 who also purchased antipsychotics at least once (to select out nonpsychiatric anticonvulsant use). Poisson regression of suicides by medication purchased (anticonvulsants or lithium) was conducted, controlling for age, sex, and calendar year. Confounding by indication was addressed by restricting the comparison to individuals prescribed the same medication: individuals with minimal medication exposure (e.g., who purchased only a single prescription of anticonvulsants) were compared to those individuals with more consistent medication exposure (i.e., purchasing ≥6 prescriptions of anticonvulsants).

Results

Demographics and frequency of anticonvulsant, lithium, or antipsychotic use were similar between lithium and anticonvulsant purchasers. Among patients who also purchased antipsychotic at least once during the study period, purchasing anticonvulsants more consistently (≥6 prescriptions) was associated with a substantial reduction in the risk of suicide (RR=0.22, 95% CI=0.11–0.42, p<0.0001), similar to patients consistently purchasing lithium (RR=0.27, 95% CI=0.12–0.62, p=0.006). Absolute suicide risks of consistent anticonvulsant and consistent lithium purchasers were similar.

Limitations

Lack of information about diagnoses and potential confounders, as well as other covariates that may differ between minimal and consistent medication purchasers, are limitations to this study.

Conclusions

In this longitudinal study of anticonvulsant purchasers likely to have psychiatric disorders, consistent anticonvulsant treatment was associated with decreased risk of completed suicide.

Keywords: Suicide, Anticonvulsants, Lithium, Pharmacoepidemiology, Longitudinal research, Confounding by indication

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PII: S0165-0327(09)00033-0

doi:10.1016/j.jad.2009.01.013

Journal of Affective Disorders
Volume 117, Issue 3 , Pages 162-167, October 2009

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