Those with methamphetamine use disorders were next highest with a 4.67-fold risk, followed by those with addictions to cannabis (3.85), alcohol (3.83) and cocaine (2.96). Alcohol dependence was related to the highest number of deaths overall.
Mortality Rates Among Drug Users
The study, available online in the journal Drug and Alcohol Dependence, is the largest North American study to compare mortality rates among different drug users with the longest follow-up. It tracked records of more than 800,000 individuals hospitalized with drug dependence between 1990 and 2005. Of this group, more than 188,000 died during this period.
The findings mean that if 10 individuals in the general population died, then over the same period there would be 57 deaths among people dependent on opioids, which includes prescription opioids as well as heroin.
"One reason for undertaking this study was to examine whether methamphetamine posed a particular threat to drug users, as it has been called 'America's most dangerous drug,'" says CAMH Scientist Dr. Russell Callaghan, who led the study. Globally, methamphetamine and similar stimulants are the second most commonly used class of illicit drugs.
High Risk of Death
"The risk is high, but opioids are associated with a higher risk. We also wanted to compare mortality risks among several major drugs of abuse, as this comparison hasn't been done on this scale before."
Alcohol dependence affected the highest number of individuals, with 166,482 deaths and 582,771 hospitalizations over the study period. In the methamphetamine group, there were 4,122 deaths out of 74,139 hospitalizations, and for opioids, 12,196 deaths out of 67,104 hospitalizations.
Specific causes of mortality were not examined in this study, so the deaths may not be directly caused by drugs but due to related injuries, infectious disease or unrelated reasons. The researchers are now exploring mortality causes for each drug group, which may also point to reasons why women had a higher risk of death for alcohol, cocaine and opioids than males.
"These are not occasional, recreational drug users, but people who have been hospitalized for drug dependence," notes co-author Dr. Stephen Kish, Senior Scientist at CAMH.
To calculate mortality rates, Dr. Callaghan and colleagues examined hospital records of all California inpatients with a diagnosis of methamphetamine, alcohol, opioid, cannabis or cocaine-related disorders from 1990-2005. They excluded records with evidence of multiple drug use disorders. The inpatient records were then matched to death records from the California Vital Statistics Database. Rates were adjusted by age, sex and race to the California population in 2000.
Risk Greater for Marijuana Users
"One surprising finding was the high rate of death among cannabis users," says Dr. Callaghan. "There could be many potential reasons, including the fact that they may have other chronic illnesses such as psychiatric illnesses or AIDS, which can also increase the risk of death."
The findings point to the importance of brief interventions for people receiving medical care for drug dependence on other related risks such as infectious diseases or injuries, says Dr. Callaghan.