The use of ketamine has increased
however, actual consumption patterns and ketamine-related deaths remain poorly understood. This study aimed to (1) cluster the consumption patterns of individuals who consume ketamine and (2) investigate their associations with manner and cause of death. A retrospective study was conducted on all cases positive to ketamine at death, retrieved from the Institute of Forensic Medicine between 2013 and 2019. A total of 414 individuals tested positive for ketamine in various samples, including blood, pleural effusion, hair, and others, with 294 individuals having detectable ketamine in their blood samples, which were subsequently clustered. The most prevalent patterns identified were ketamine plus alcohol (49.5%), ketamine plus new psychoactive substances (39.1%), and ketamine plus methamphetamine (24.4%). Drug intoxication was the most reported cause of death, followed by traffic accidents. Cluster 1 exhibited moderate ketamine concentrations (1.7 µg/mL), a high prevalence of polydrug use (85%), and an increased risk of suicide. Cluster 4 displayed very low ketamine concentrations (0.13 µg/mL) but similarly high rates of polydrug use (85%) and an elevated risk of accidental death. The concurrent use of ketamine and alcohol, primarily categorized within cluster 3, accounted for nearly half of the deaths resulting from drug intoxication or traffic accidents. Our study underscores the potential dangers of using ketamine as one of multiple substances. Our study also emphasized the critical role that consumption patterns and dosages play in determining the potential lethal outcomes associated with ketamine. In the future, medical applications of ketamine must consider patients' use of other substances and inform them of the associated risks.