Suicide by paraquat poisoning in Taiwan and potential prevention strategies

Research aims and hypotheses
Pesticide ingestion accounts for one fifth of global suicides and is a major public health problem in low- and middle-income countries. Paraquat, a commonly used weed killer that is highly lethal when ingested in suicide attempt, accounts for around 200 suicides (5% of all suicides) in Taiwan a year. On 5th October 2017, Taiwan introduced new regulations to ban paraquat use from 1st February 2020 onwards. Few studies have prospectively investigated the effectiveness, cost-effectiveness and impact on crop yields of such a ban. We aim to investigate the effectiveness and cost-effectiveness of the ban on paraquat to reduce suicide in Taiwan. We hypothesize that the paraquat ban will be followed by a decrease in paraquat suicide and pesticide suicide in Taiwan, and overall suicide in rural areas where paraquat accounts for a significant proportion of overall suicides (~15%). The intervention will be cost-effective. The overall fatality of pesticide self-poisoning will decrease, and there will be no impact on crop yields. Patients who ingested paraquat are not more likely to have psychiatric disorders than those who ingested other pesticides.

Sample
The evaluation will be based on the whole Taiwanese population (23 million). Data for suicide (2002-2020) and self-harm (2015-2020) by paraquat poisoning will be extracted from national death and self-harm registries. Hospital records of 2,660 patients who ingested pesticides in 2000-2020 will be examined. The hospital record collection will benefit from the collaboration established in a pilot study that has extracted data for 1,035 patients from six hospitals in different regions of Taiwan.

Measures
The main outcomes of the effectiveness analysis include suicide and self-harm rates by paraquat poisoning, pesticide poisoning, and all methods. In the cost-effectiveness analysis, costs involve expenses of enforcing the paraquat ban and subsidising substitute weed-killer products; effects will be assessed by life year and healthy life year gained. Additional benefits include loss of productivity (income) due to premature death and costs of hospital stay from paraquat self-poisonings averted. Hospital data extraction includes a wide range of variables such as length of hospital stay, psychiatric disorders, pesticides ingested, and outcome at discharge.

Procedures
The effectiveness analysis will examine change in suicide rates by applying rigorous methodology that takes into account suicide trends before the paraquat ban. The cost-effectiveness analysis will report the ratio of US$ or International dollar per one life year gained from the paraquat ban. 

Potential impact
The project has the potential to not only inform strategies for reducing the incidence of pesticide suicide in low-income countries or agricultural regions, but also have relevance to suicide prevention by restricting other methods such as opioid overdose and firearms.

Next steps in this line of proposed research
We intend to investigate the longer-term effect of paraquat ban on reducing suicide in the future. Findings from the current study will be disseminated to policy makers responsible for pesticide regulation and inform suicide prevention strategies in countries where pesticide ingestion accounts for many deaths that are preventable by banning highly lethal pesticides such as paraquat.