Aim: The purpose of this qualitative study was to investigate the effects experienced by users of a novel psychoactive substance, the benzodiazepine flubromazolam, by analysing users' own accounts on the Swedish forum Flashback.org. Method: A thematic analysis of anonymous self-reports published on the forum was performed and generated five general themes describing effects and experiences by flubromazolam users. Results: The themes which emerged were: Onset and duration, Desired effects, Adverse effects and addiction, Loss of control, General estimations and evaluations. The main reported characteristics of flubromazolam were heavy hypnotic and sedative effects, long-lasting amnesiac effects and the rapid development of tolerance. Flubromazolam was also anxiolytic and acted as a muscle relaxant for many users. Some users experienced euphoria or intense wellbeing. Other prominent characteristics were loss of control (leading to poor choices and actions, with unpleasant consequences) and long-lasting, often severe withdrawals. There were also serious incidents where users had been admitted to hospital, acute psychiatric treatment or taken into custody by the police. Conclusion: Flubromazolam appears to be a highly addictive and precarious benzodiazepine with many, possibly severe, side effects. The substance is generally described as very potent and with long-lasting effects. Memory loss and loss of control are common adverse effects, and withdrawals appear to be severe for many users