The World Health Organization now includes ‘Gaming disorder’ in the 11th revision of its International Classification of Diseases. We need more independent research into design features that can contribute to addictive and harmful gaming, particularly with respect to technological innovations such as machine learning and in-game purchasing (‘microtransactions’).

Players’ vulnerability, along with social and environmental factors, influences the onset, progression and recurrence of harmful gaming. Games are unregulated products designed to capture users’ attention and promote endless play.

Companies often engineer and fine-tune games to deliver constant and immediate rewards, complex narratives, immersive virtual environments and social reinforcement. Game technologies can monitor and learn from gamers’ behaviour, and adapt their content accordingly. Monetized mobile games use behavioural tracking to alter in-game conditions to incentivize continuous spending and persistent playing.

Studies have so far focused on the likes of massively multiplayer online role-playing games (World of Warcraft, for example). But these have now been outpaced by the multiplayer online battle arena (typified by League of Legends), and the battle royale genre (Fortnite and the like). Researchers must rethink how to map the effects of gaming on children and adolescents.

Understanding dangerous player–game interactions should promote more-ethical game designs and so help people for whom gaming has become a problem.