INTRODUCTION AND AIMS: To assess the demographic profile, use patterns, market characteristics, reasons for first use and self-reported harms associated with use of synthetic cannabinoids in Australia. DESIGN AND METHODS: An online questionnaire was administered to a purposive sample of 316 Australian synthetic cannabinoid users [96% cannabis users, 77% male, median age 27 years, interquartile range (IQR) 23-34] who self-reported demographic and drug use characteristics. RESULTS: The median duration of synthetic cannabinoid use was 6 months (IQR 2-10), 35% reported use weekly or more often and 7% reported daily use. Reasons for first use included curiosity (50%), legality (39%), availability (23%), recreational effects (20%), therapeutic effects (9%), non-detection in standard drug screening assays (8%) and to aid the reduction or cessation of cannabis use (5%). Users reported buying a median of 3 g (IQR 3-6) and paying a median of AU$60 (IQR 37-90). Most (68%) reported at least one side-effect during their last session of use, including decreased motor co-ordination (39%), fast or irregular heartbeat (33%), dissociation (22%), dizziness (20%), paranoia (18%) and psychosis (4%). 4 respondents reported seeking help. A greater number of side-effects were reported by males, those aged 18-25 years, water pipe (‘bong’) users and concurrent alcohol drinkers. DISCUSSION AND CONCLUSIONS: The sample reported first using synthetic cannabinoids due to curiosity, legality, availability, effects, non-detection in drug testing and to reduce their cannabis use. Harms were widely reported yet help-seeking was minimal. Inclusion of questions regarding synthetic cannabinoids in household surveys is warranted.