Analysis of poisoning suicides warns of opioids, sedatives, tricyclic antidepressants

Key takeaways:

• Poisoning suicides involved opioids and sedatives more often than non-poisoning suicides.
• Tricyclic antidepressants were more associated with poisoning suicides than selective serotonin reuptake inhibitors.

An analysis of poisoning-related suicides in Australia identified several substances to be careful about prescribing, while finding that “many medicines are present at lower levels,” even in non-poisoning suicides.

The findings suggest that the most common substances in poisoning-related suicides — such as tricyclic antidepressants, sedatives and opioids — should be prescribed cautiously or monitored, researchers wrote in JAMA Psychiatry. They also highlighted relationships between suicide, poor mental health and substance misuse.

The cross-sectional study examined suicides from July 2013 to October 2019 using postmortem toxicology data from Australia’s National Coronial Information System. The researchers deemed suicides poisoning-related if coroners mentioned poisoning as a contributing factor of death (ie, even if the suicide also involved hanging).

The study included 13,664 decedents (median age, 44 years; 76% men), 24.9% of whose suicides were classified as poisoning-related (median age, 50 years; 63% men). Medicine or drugs, including illicit drugs, were factors in 62.8% (n = 2,132) of poisoning-related suicides, while nontherapeutic gases or chemicals were involved in the other 37.2% (n = 1,265).

Non-poisoning related suicides totaled 10,267. Mixed methods, such as poisoning and hanging, occurred in 633 cases.

The substances with the highest prevalence ratios (PR), indicating they were seen more often in poisoning-related suicides, were:

• non-therapeutic gases and chemicals (PR = 3.1; 95% CI, 2.94-3.27);
• opioids (PR = 2.72; 95% CI, 2.58-2.87);
• antiepileptics (PR = 2.67; 95% CI, 2.51-2.84);
• other central nervous system agents (PR = 2.67; 95% CI, 2.37-3);
• gastrointestinal, including antiemetics (PR = 2.51; 95% CI, 2.33-2.71); and
• sedatives (PR = 2.36; 95% CI, 2.14-2.6).

The researchers also determined which substances were seen in poisoning-related suicides at particularly elevated concentrations. To do this, they went through each substance and calculated the percentage of poisoning-related suicides at which it appeared in a concentration exceeding its P90 value — the level it was measured below in 90% of all the suicides, both poisoning- and non-poisoning-related.

Substances most often observed above their P90 concentrations in poisoning-related suicides included:

• amitriptyline and nortriptyline (100% of observations);
• tramadol (100% of observations);
• quetiapine (98% of observations);
• oxycodone (96% of observations); and
• codeine (95% of observations).

Compared with selective serotonin reuptake inhibitors, tricyclic antidepressants were more likely to appear in poisoning-related suicides, particularly at higher concentrations. While unable to draw a causal connection, the researchers said that the finding is consistent with case fatality studies.

Non-poisoning suicides more commonly involved amphetamines (PR = 0.68; 95% CI, 0.61-0.77) and cannabinoids (PR = 0.67; 95% CI, 0.6-0.74). Amphetamines, cannabinoids and SSRIs were all more likely to appear at higher concentrations in non-poisoning suicides.

Alcohol — as ethanol greater than or equal to 0.03 g/100 mL — was almost as prevalent in poisoning suicides as non-poisoning suicides (PR = 1.07; 95% CI, 1.01-1.14). The study emphasized alcohol exposure as a “modifiable risk factor for suicide.”

Limitations to the study included incomplete toxicological data, either because some areas did not routinely analyze certain substances or some substances, like gases, had dissipated. The researchers said their data should not be used to draw causal links between substances and suicides, noting their lack of a control population.

The study suggests several substances to target with means restriction or more cautious prescribing, including oxycodone, codeine, amitriptyline, pentobarbitone, pregabalin, propranolol, quetiapine, venlafaxine and tramadol.

The researchers recommended that patients with suicide risks first be prescribed less-toxic agents or longer-acting treatments, adding that safe storage and disposal of unnecessary or unwanted medicines can also reduce the lethality of overdose suicides.