Abstract: Much theory asserts that sexual intimacy sustains mental health. Experimental tests of such theory remain rare and have not provided compelling evidence because ethical, practical, and cultural constraints bias samples and results. An epidemiologic approach would, therefore, seem indicated given the rigor the discipline brings to quasi-experimental research. For reasons that remain unclear, however, epidemiologist have largely ignored such theory despite the plausibility of the processes implicated, which engender, for example, happiness, feelings of belonging and self-worth, and protection against depression. We use an intent-to-treat design, implemented via interrupted time-series methods, to test the hypothesis that the monthly incidence of suicide, a societally important distal measure of mental health in a population, decreased among Swedish men aged 50–59 after July 2013 when patent rights to sildenafil (i.e., Viagra) ceased, prices fell, and its use increased dramatically. The test uses 102 pre, and 18 post, price-drop months. 65 fewer suicides than expected occurred among men aged 50–59 over test months following the lowering of sildenafil prices. Our findings could not arise from shared trends or seasonality, biased samples, or reverse causation. Our results would appear by chance fewer than once in 10,000 experiments. Our findings align with theory indicating that sexual intimacy reinforces mental health. Using suicide as our distal measure of mental health further implies that public health programming intended to address the drivers of self-destructive behavior should reduce barriers to intimacy in the middle-aged populations.
Our findings support the intuition and theory that sexual intimacy involving male erection protects against suicide among older men. Our methods ensure that this association could not arise from shared trends or seasonality, biased samples, or reverse causation. We further note that our finding would appear by chance fewer than once in 10 000 experiments (i.e., point estimate of − 4.66 with a standard error of 0.94) and that they align with theory indicating that sexual intimacy reinforces mental health.
Only replication can determine whether the association we found in Sweden describes other societies in which changes in patent rights affected the availability of sildenafil. We, however, know of no reason to suspect that the association would appear only in this cohort of Swedish men.
Although using suicide as an outcome connects our theory to an objective and important phenomenon, it likely leads to an underestimate of the association between low-priced sildenafil and mental health because suicide remains an extreme manifestation of diminished well-being. We could not, moreover, test for any unintended adverse health consequences (e.g., changes in sexually transmitted diseases).
Our methods do not estimate the efficacy of sildenafil in reducing an individual’s suicide risk. We assume that the rapid increase in the use of sildenafil among Swedish men in late 2013 arose in large part due to the availability of low-priced generic sildenafil. We, however, could not access monthly information on price, volume of prescriptions, or age of patients receiving these prescriptions. An important extension of our study would involve such data as well as longitudinal information on men’s mental health and likely mediating processes before and after July 2013. Such data would allow individual-level tests of whether and how the novel use of sildenafil improved mental health among men in their 50′s.
We speculate that the difference between expected and observed suicides declined below statistically detectable levels, although did not disappear, in 2015 for at least two reasons. The first assumes that lowering the price of sildenafil in 2013 likely reduced erectile dysfunction among men regardless of age. When men younger than 50 in 2013 eventually aged past 50, the sequelae of erectile dysfunction, including an increased risk of suicide, appeared lower among them than among men 50 to 59 when the price of sildenafil dropped.
Second, counterfactuals in tests that, like ours, use autocorrelation to arrive at expected values eventually “adjust” for interruptions with persistent effects. The effects, in other words, become statistically expected. Our test, for example, found autocorrelation such that an unexpected value at month t influences expectations for month t + 6. Our counterfactuals for 2015, therefore, reflected not only the pre-generic price months but also the lower-than-expected values observed in 2013 and 2014. We note, however, that the alternative approach of using forecasts in 2013 and 2014 to estimate expected values farther in the future would provide no more certainty than our approach because detection intervals in such models expand relatively quickly.
We did not hypothesize a detectable decline in suicide among women aged 50 to 59 because underlying causal processes, such as the etiology of depression [33], may differ between women and men. The failure to find an association, however, requires comment if for no other reason than sexual intimacy also relates to the mental health of women [7, 8]. Although the comparatively low incidence of suicide among women makes detecting differences over time less certain, we note that the null finding could arise from differences between men and women in the purpose and meaning of male erection as a component of intimacy at this stage of life [7]. For example, having and maintaining an erection may contribute directly to a man’s confidence and self-esteem [5], while insofar as this contributes to such self-perceptions among a female partner it would do so indirectly, as through a sense of desirability [34], with the respective effects possibly changing differentially with age across the genders [35]. The present data, however, do not enable us to do more than speculate on such possibilities. We can only acknowledge the complexity of the individual and contextual determinants of suicide rates and the need for further attention to the role that sexual intimacy plays in suicide, as encouraged by our strong epidemiologic findings.
Our results appear consistent with the general argument that many people enjoy sexual intimacy as a fundamental component of relationships that confer wellbeing and good mental health. Means to overcome erectile dysfunction could, therefore, promote restoration of a relational resource diminished by an inability to share desired forms of intimacy. These means likely include not only pharmaceutical treatment, but also individual or couple’s counselling, behavioral therapy [36], or even public policies (e.g., vacation legislation) that allow people more time for sexual intimacy. Insofar as salutary relationships remain important not only for the partners but also for the people around them and for the organizations to which they contribute, interventions such as greater access to sildenafil likely produce benefits to society.
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