Association Between Means Restriction of Poison and Method-Specific Suicide Rates: A Systematic Review

Abstract

Importance: Suicide is a major and preventable cause of death worldwide. Means restriction aims to reduce the rate of completed suicides by limiting public access to lethal suicide methods. Means restriction of agents used in poisoning is more controversial because there is potential to switch to other lethal methods.

Objective: To identify the changes in suicide rate by the targeted poison and the corresponding changes in suicide by other methods.

Evidence review: Five databases (MEDLINE, Embase, Scopus, PsycInfo, and Web of Science) were searched for studies on national means restriction of poison that were published in the English language from inception until December 31, 2019. Of the 7657 articles that were screened by title and abstract, 62 studies were included in the analysis.

Findings: Sixty-two studies from 26 countries in Europe, the US, Australia, Asia, and the United Kingdom were included in the review. The studies included restrictions on pesticides (15 countries), domestic gas (14 countries), motor vehicle exhaust (9 countries), and pharmaceuticals (8 countries). The median (IQR) change in method-specific suicide rates was -1.18 (-2.03 to -0.46) per 100 000 people after restrictions, whereas the median (IQR) change in other methods of suicide (not the restricted poison) was -0.09 (-2.22 to 1.65) per 100 000 people. Decreases in suicide by the restricted poison were not associated with increases in suicide by other methods. An estimated 57 355 poison-specific suicides annually (before the interventions were implemented) may have benefited the most from means restriction.

Conclusions and relevance: This systematic review found that means restriction of poison was associated with decreased method-specific suicide rates without an equivalent shift toward the use of other methods. Suicide prevention strategies need to address both individuals who are at risk and population-level policies.

Figure 1.. Forest Plots for Changes in Suicide by Pesticide and Suicide by Other Methods

Blue squares indicate ban of pesticide; NA, not applicable; orange squares, occupational license. ^aData on overall suicide or other methods of suicide were not available.

Figure 2.. Forest Plots for Changes in Suicide by Domestic Gas and Motor Exhaust and Suicide by Other Methods

In panel B, blue squares represent catalytic converter, and orange squares represent (4.5% emission) of carbon monoxide in cars. NA indicates not applicable. ^aData on overall suicide or other methods of suicide were not available.

Figure 3.. Forest Plots for Changes in Suicide by Drug Overdose and Suicide by Other Methods

Barbiturates in Japan were up-scheduled to prescription-only access. Barbiturates in Sweden and Denmark and dextropropoxyphene in Denmark were placed under therapeutic restriction. Barbiturates in Australia and paracetamol in England and Wales had pack-size limits. Dextropropoxyphene in England and Wales was withdrawn from the market. ^aIndicates studies that recorded suicide by a broader drug class (eg, analgesic and sedative).

Figure 4.. Scatterplot With Linear Regression of Change in Suicide by Restricted Methods vs Change in Suicide by Other Methods

Line-of-fit metric y = −0.058x – 1.621 with x representing the change in suicide by other methods; linear regression slope = −0.06 (95% CI, −0.25 to 0.14). Inset, the quantile-quantile (QQ) plot shows a normal distribution.