June 13, 2006
Did Prozac Lower Suicide Rates?

In a paper published in Plos Medicine a team of researchers found that rises in the use of Prozac appear negatively correlated with suicide rates.

What Did the Researchers Do and Find?

They looked at annual suicide rates between 1960 and 1988 and compared them with annual rates in the period 1988 to 2002. They used several sources of data, including the Centers of Disease Control and the US Census Bureau. The researchers found that from the early 1960s until 1988, in the entire US population, between 12.2 and 13.7 people in every 100,000 committed suicide each year. After that time, the numbers of suicides gradually declined, with the lowest figure (10.4 people per 100,000) reached in 2000. The researchers did mathematical tests, which demonstrated that the steady decline was statistically associated with the increased number of fluoxetine prescriptions—that is, the more prescriptions there were, the fewer suicides there were. (There were around two-and-a-half million prescriptions of the drug in 1988, increasing to over 33 million in 2002.)

What Do These Findings Mean?

In all scientific research, it is an important principle that finding an association between two events does not prove that one caused the other to occur. However, the authors of this paper suggest that the use of this drug could have contributed to the reduction of suicide rates in the US in the period 1988 to 2002. Several other SSRIs are also now in common use, but they were not considered in this study, nor were other antidepressants, or other treatments for depression.

Prozac belongs to a class of anti-depressants known as Selective Serotonin Uptake Inhibitors (SSRIs). They work by blocking proteins on nerve cells that transport the serotonin into the nerves. That causes serotonin concentrations to rise in gap regions between nerves and ttherefore to bind instead to receptors to increase the effect of serotonin in sending messages that (at least in theory) will lighten moods.

Here is the paper.

Methods and Findings

Sources of data included Centers of Disease Control and US Census Bureau age-adjusted suicide rates since 1960 and numbers of fluoxetine sales in the US, since its introduction in 1988. We conducted statistical analysis of age-adjusted population data and prescription numbers. Suicide rates fluctuated between 12.2 and 13.7 per 100,000 for the entire population from the early 1960s until 1988. Since then, suicide rates have gradually declined, with the lowest value of 10.4 per 100,000 in 2000. This steady decline is significantly associated with increased numbers of fluoxetine prescriptions dispensed from 2,469,000 in 1988 to 33,320,000 in 2002 (rs = −0.92; p < 0.001). Mathematical modeling of what suicide rates would have been during the 1988–2002 period based on pre-1988 data indicates that since the introduction of fluoxetine in 1988 through 2002 there has been a cumulative decrease in expected suicide mortality of 33,600 individuals (posterior median, 95% Bayesian credible interval 22,400–45,000).

Conclusions

The introduction of SSRIs in 1988 has been temporally associated with a substantial reduction in the number of suicides. This effect may have been more apparent in the female population, whom we postulate might have particularly benefited from SSRI treatment. While these types of data cannot lead to conclusions on causality, we suggest here that in the context of untreated depression being the major cause of suicide, antidepressant treatment could have had a contributory role in the reduction of suicide rates in the period 1988–2002.

For a number of reasons this study does not prove a causal relationship between Prozac usage and lower suicide rates.

As the authors acknowledge, suggestions that there may be a causal relationship between fluoxetine prescription and suicide rates would represent an overinterpretation of the results. In a study like this, it is also important to consider other potential explanations for the fall in suicide rates, such as improvements in the economy or improved management of depression by primary-care providers. Moreover, as the study did not include people above 65 years of age, who are known to have an increased risk of suicide (especially in men) compared with younger people, the findings are limited to adults up to 65 years of age.

Another limitation of this study was the use of fluoxetine as a model of SSRI use. Several effective SSRIs have been introduced since the arrival of fluoxetine, and these newer SSRIs may have had an additional potential impact on suicide rates. Finally, although the authors used the best available data on the number of prescriptions of fluoxetine, these estimations are not very accurate in terms of actual intake of antidepressants. As there are no reliable figures available on adherence to drug prescriptions at the population level, the real effect of antidepressants on suicide rates is difficult to estimate.

Even if this result holds up and the SSRIs have prevented 33,000 deaths that is probably small potatoes compared to the benefits in reduce mortality that have flowed from use of statin drugs to lower cholesterol. However, if SSRIs are brightening moods then they are probably making a big economic impact by reducing the lethargy that comes with depression.

Share |      Randall Parker, 2006 June 13 10:36 PM  Brain Disorder Repair


Comments
James Bowery said at June 14, 2006 5:10 AM:

What an ecological study like this does is provide justification for investment in further testing the hypothesis at the case history level.

Andrew Berman said at June 14, 2006 7:05 AM:

My understanding of high-risk cases (I have personal experience with a few of them) is that they're often on combinations of drugs. Separating out the effect of one drug on the suicide risk is probably impossible and meaningless.

Prozac, Zoloft, Xanax--- proof that ultimately, God does love the Jews. :)

Jake said at June 14, 2006 8:16 AM:

One doctor said that the miracle drug that would greatly increase the quality of life for people over 60 would be a cocktail made up of:

1. Statins for clean arteries
2. Ace inhibitors for blood pressure and other coronary ills.
3. SSRIs for depression that is prevalent among the elderly

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