Abstract Background Gambling products differ in terms of their harm potential. Products are also constantly developing and changing. However, little research has addressed changes and trends in the types of gambling that are associated with harms. The current study explores trends in the gambling product categories identified as harmful in longitudinal helpline data from three Nordic countries. Methods We use data collected by national helplines in Denmark (StopSpillet), Finland (Peluuri) and Sweden (Stödlinjen) in their daily operations (N = 46 646). The data consist of information collected on gamblers and concerned significant others who have contacted these helplines between January 2019 and December 2022. We analyse which gambling products are mentioned as harmful by clients. The analysis uses linear regression with the interaction term (country) times time regressed over the outcome variable (proportion per month). Results The results show that an increased share of contacts concern online gambling. Online casino products have become the most harmful category across contexts. The share of reported harms from online betting and new emerging online forms is also increasing. The share of land-based products as a reported source of harms has decreased across 2019–22. Conclusions The results suggest that online gamlbing environments, and particularly online casino products, are associated with increasing harms to help-seekers. The harmfulness of different gambling products may not be stable, but change over time. Further harm prevention efforts are needed to address the online gambling field, including emerging formats.