Substance use was implicated in more than half of all adult drownings in baths or hot tubs in the last 10 years, according to an Australian-first study published in Drug and Alcohol Review.
Sedative-hypnotics (or 'sleeping tablets') and alcohol were the most frequently detected substances, said researchers led by the National Drug and Alcohol Research Centre (NDARC) at UNSW Sydney.
And while the majority of the 195 cases identified were deemed unintentional, just over a third of these drownings were due to suicide.
"These were tragic deaths, and substance use was prominent and formally judged to be contributory in a majority of these cases" said Emeritus Professor Shane Darke, lead author of the study.
"It's notable that one in four had a history of substance use problems."
While intoxication is widely recognised as a risk factor in ocean, river and pool drownings, the authors said the role of substance use in bathing-related deaths had not received much public attention.
"In fact, at least 5% of drownings occur in a bath or hot tub, the majority of which involve drugs," Professor Darke said.
"Public safety awareness campaigns that focus on the potential dangers of substance use in baths and hot tubs would appear prudent if we are serious about reducing drownings in general."
What did the study find?
As part of the retrospective study, Professor Darke and colleagues reviewed all adult drowning deaths in baths or hot tubs in Australia between 2015 and 2024.
The cases were retrieved from the National Coronial Information System (NCIS), which is a database of medicolegal death investigation records provided by the coroners' courts in each Australian jurisdiction.
Of the 195 cases identified, two-thirds were female, the average age was 55 years, and the vast majority of incidents occurred in a bath.
Overall, substance use was prominent and deemed contributory to death in the coronial conclusions of 113 cases (58%).
A history of substance use problems was documented in 28% of cases, and 52% had a history of mental health problems.
The authors found that while most (55%) were found to be accidental, over a third (37%) of these drowning deaths were deemed intentional, and the intent was unable to be determined in a small number of cases.
In 33 individuals, there appeared to have been a medical episode – most commonly a suspected seizure or cardiovascular event – before the drowning event.
An acute injury was noted in 24 cases, of which most were the result of a slip or fall before the drowning event.
Blood toxicology test results showed that a drug was detected in 85% of cases, with sedative-hypnotics (43%) and alcohol (42%) the most common drugs.
Among cases where alcohol was detected – either alone or with other substances – the average blood alcohol concentration was 0.176%, more than three times the legal driving limit.
"The risk of drowning in such settings in the presence of drugs needs to be widely appreciated," the authors concluded.
"Public campaigns that focus on the potential dangers of substance use in these settings would appear prudent."
