Illicit drug use may accelerate coronary disease and cardiac hypertrophy or stimulate arrhythmias. Rates of illicit drug use in young patients with sudden cardiac death (SCD) are uncertain.The purpose of this study was to identify rates of illicit drug use in young patients with SCD.A prospective statewide registry identified out-of-hospital patients with cardiac arrest aged 18-50 years from April 2019 to April 2021. Clinical characteristics were compared between patients with and without illicit drug use (defined by toxicological results or reported regular use). Illicit drugs included amphetamine-type substances, cocaine, heroin, cannabis, and other drugs.A total of 554 (40.2%) of 1378 patients had confirmed cardiac cause of out-of-hospital cardiac arrest, with 523 undergoing toxicological assessment. There were 170 patients (32.5%) having either positive toxicology for illicit drugs (n = 138) or negative toxicology but reported regular drug use (n = 32). Patients with SCD and illicit drug use were more commonly male (81.2% vs 72.3%; P = .028), smokers (38.8% vs 19.8%; P ≤ .0001), and excess alcohol drinkers (30.6% vs 20.6%; P = .012) and had a psychiatric diagnosis (38.8% vs 25.7%; P = .002), lower body mass index (29.4 kg/m vs 31.7 kg/m; P = .0063), and lower rates of hypertension (10.6% vs 18.6%; P = .019). Death commonly occurred while sedentary (47.5%) or during sleep (45.8%). Accounting for these baseline differences, there were no differences in rates of coronary disease or cardiomyopathy. Cannabis (n = 106) was the most common illicit drug identified and polysubstance abuse occurred frequently (n = 25).2Approximately one-third of young patients with SCD have positive toxicology at the time of death or reported frequent use of illicit drugs, with high rates of polysubstance abuse.