The sales of antidepressants and suicide rates in Norway and its counties 1980–2004

Abstract

Background

Suicide is a major public health problem and depression is among the most important risk factors for suicide. Treatment of depression might prevent suicide. To study this hypothesis further we conducted an ecological study.

Methods

An ecological study using sales data for antidepressants and numbers of suicides in Norway and Norwegian counties 1980–2004 was performed. Data on alcohol consumption and unemployment rates were registered and taken into account. Data were analyzed using Cochrane-Orcutt time series for the country as a whole. The county specific data were analyzed with a random coefficient model with county as subject and intercept and time (slope) as random variables using an unstructured covariance matrix.

Results

Sales of non-tricyclic antidepressants (non-TCAs) and suicide were clearly negatively related, even when controlling for alcohol and unemployment (adjusted r²: 0.57). There was an effect modification between time and level of sales of non-TCAs. Studying the relationship between the sales of non-TCAs and the suicide rate, we found that it was significant and stronger for the low sales figures, but non-existent for the high sales figures.

Limitations

Ecological studies cannot infer causality.

Conclusions

The fall in suicide rates in Norway and its counties was related to the increased sales of non-TCAs. The effect was mostly a result of a sales increase in the lower sales segment, indicating that a change from the more toxic TCAs, or heightened awareness of depression and its treatment, could explain the relationship found between sales of newer antidepressants and a decrease in suicide rate.

Introduction

Mental health disorders are important causes of suicide (Harris and Barraclough, 1997), and particularly important are affective disorders, because different subtypes are found among about 60% of suicides in the general population (Cavanagh et al., 2003). The risk of suicide also increases with the severity of the depressive episode (Kessing, 2004). Treatment of such conditions is thought to be beneficial in the prevention of suicide. The introduction of newer antidepressants, and especially the selective serotonin reuptake inhibitors (SSRIs), at the start of the 1990s accelerated the diagnosis and treatment of depression. Far more people were exposed to drugs that could alleviate depression. Together with this increase in sales of antidepressants, many western countries experienced a decline in their national suicide rates. Several researchers, particularly Isacsson (Isacsson, 2000), have promoted the idea that these two phenomena are related and increased treatment of depression has led to the observed decline.

Although suicide is a major public health issue, it is a rare phenomenon at an individual level. Only very large, possibly unsustainable, randomized controlled trials (RCTs) would, by themselves, have enough power to demonstrate any difference in suicide rate between a treatment and a placebo. Meta-analysis of such studies could, to some extent, overcome this (Khan et al., 2003, Gunnell et al., 2005). The follow-up time of RCTs included in the meta-analysis is, however, too short to capture the whole at-risk period for suicide in connection with depression. Furthermore, suicidality is usually an exclusion criterion in such trials, because of ethical constrains and practical difficulties.

Ecological investigations into the relationship between the sales of newer antidepressants and suicide rates have been performed in several countries, with varying time spans, different age groups, and various types of co-variates and statistical approaches (Table 1). With the exception of the studies in Iceland, Italy and Slovenia, which have not shown a decline in suicide rates, most of these studies find that the increased sales of newer antidepressants seem to be related to the decrease in suicide rate. This is also found in other communications from Hungary (Rihmer et al., 2001, Rihmer, 2003) and Britain (Gunnell and Ashby, 2004). What separates them are the result interpretations, ranging from a belief in a causal relationship to stating that sales figures are indirect measures of better diagnosis of depression and more treatment optimism, or even that the relationship is purely spurious.

The aim of the current study was to investigate the relationship between antidepressant sales and suicide rates as seen in Norway as a whole, and in its counties, on the basis of observations made from 1980 to 2004. As a completed suicide is not just a matter of mental illness and its treatment, we also included data on alcohol consumption and unemployment as confounders, both of which have been found to be related to national suicide rates (Rossow, 2005, Platt and Hawton, 2006).