Suicide is a complex, major public health issue globally. While people who use drugs (PWUD) are known to be at increased risk of suicide, there is limited information on the specific candidate risk factors for this group, which could help to inform targeted interventions to reduce their risk. To this end, a scoping review was conducted with three aims: (1) to map the extent, range, and nature of available evidence on factors associated with death by suicide among PWUD; (2) to identify knowledge gaps and limitations in this body of evidence; and (3) to inform suicide prevention policy and best practice guidelines for working with PWUD, where appropriate.1

Methods

The aim of scoping reviews is to systematically search for and then map all the evidence in relation to the research question. Scoping reviews encompass all available literature, both published and grey, with stakeholder consultation an important component. Unlike systematic reviews, this method in general does not include a quality appraisal of the literature.

Results

In total, 12,395 items published between 2000 and 2021 were identified, but following a screening process (e.g. removing duplicates; non-English language; insufficient data) only 53 items were included in the review. Most of the eligible studies were based on primary research (mainly uncontrolled retrospective studies), while the secondary research included literature reviews, reports, and editorials.

Eleven potential candidate risk factors for death by suicide among PWUD were found: sex; mental health conditions; periods of heightened vulnerability; age profile; use of stimulants, cannabis, or new psychoactive substances; specific medical conditions; lack of dual diagnosis service provision; homelessness; incarceration; intravenous drug use; and race or ethnicity. Some of the literature associated with each of the candidate risk factors is highlighted below; however, as this was a scoping review and not a systematic review, the findings must be interpreted as such.

Sex

Male sex as a risk factor featured in over one-half of the studies. However, some of the studies did find an increased risk among women who used drugs compared with men, for example, in relation to potential years of life lost. In the studies that only included women who used drugs, the risk of death by suicide was linked to high levels of mental health issues.

Mental health conditions

Two-fifths of the included publications cited mental health conditions as a candidate factor, with depressive disorders most frequently mentioned. Two studies among people who used opioids found high rates of depressive disorders or history of suicide attempts (between 65% and 89%), but the overall number of suicide deaths was low. 

Periods of heightened vulnerability

The literature pointed to vulnerable periods where the risk of suicide was heightened. This included commencing or stopping opioid agonist treatment (OAT), disengaging/leaving health services, and (for women) the first months of imprisonment.

Age profile

Of the seven publications that included an age profile, most indicated that younger PWUD were at risk of death by suicide, although the definition of ‘younger age’ varied (from teens to those in their forties) across the publications. Of the studies that focused on opioid use, one found that being older when starting treatment conferred a higher risk of suicide.

Use of stimulants, cannabis, or new psychoactive substances

Stimulants (including cocaine), cannabis, or new psychoactive substances (NPS) were the focus of some studies. Six studies found that the use of these substances were potential candidate risk factors for violent non-poisoning suicide deaths, for example, by hanging. This suggests that these drugs may increase impulsivity and risk-taking, leading to a more violent manner of death.

Specific medical conditions

Blood-borne viruses were the most common conditions cited in the studies, with HIV infection in particular linked as a candidate risk factor for people who used opioids. However, history of cancer and chronic pain were also found as risk factors among people who used opioids.

Lack of dual diagnosis service provision

Some of the issues found were in relation to non-integrated addiction services and mental health services as well as poor levels of diagnosis or treatment of dual diagnosis. However, all highlighted the complex medical and psychological needs of this group.

Homelessness

While there is a higher rate of homelessness among PWUD compared with the general population, three studies did show that being homeless increased the risk of death by suicide in both men and women who use drugs.

Incarceration

Two of the three studies that identified incarceration as a candidate factor showed a clear link between lack of OAT in prison and increased risk of death by suicide.

Intravenous drug use

Three studies identified a history of intravenous drug use as a potential candidate risk factor, in particular poly-intravenous drug use. One study identified a higher risk for men compared with women.

Race or ethnicity

While only two studies found race or ethnicity as a risk factor, both were cohort studies (despite relatively dated data). An Italian study found a higher risk of suicide for people who used heroin and who were born outside Italy. An American study found that cocaine use was associated with a higher risk of suicide among African Americans compared with White Americans.

Issues for consideration

A significant number of the studies related to people who used opioids, perhaps because of existence of well-established OAT registers, where data on this population are readily available. The impact of drugs other than opioids also needs to be considered, such as cannabis as the most commonly used substance globally. 

Strengths and limitations

This is the first scoping review on factors associated with death by suicide in PWUD. While the strength of the review is that it includes all types of literature, it does not include any in-depth assessment of the quality of the evidence.

Other limitations were an over-representation of articles from Europe and Australia. As many of the American articles overlapped with military veteran research, they did not meet the strict criteria of this scoping review. There was also over-representation of people with HIV in relation to studies on intravenous drug use and blood-borne viruses, meaning that this may be a potential confounder.

Therefore, these specific candidate risk factors for PWUD should be considered when developing suicide prevention policies. Additionally, there is a need for better-quality robust, prospective primary research among PWUD to gain a greater understanding of the risk factors associated with suicide in this group.

1    Devin J, Lyons S, Murphy L, O’Sullivan M and Lynn E (2023) Factors associated with suicide in people who use drugs: a scoping review. BMC Psychiatry, 23: 655. Available from: https://www.drugsandalcohol.ie/39507/