Context: Pathological gambling is recognized as a public health issue in a many countries. Consequently, helping individuals control their gambling behaviors is critical. One strategy is setting a pre-committed limit for how much money one can lose, deposit or win. The aim of the study was to compare gambling intensity between online gamblers prompted to set a deposit limit and non-prompted customers.

Methods: All customers of the gambling service having registered an account during the study recruitment period were included. Gambling intensity was measured with aggregated net loss, with proportions of limit-setters, sum of deposits and number of gambling days used as secondary outcomes.

Intervention: A total of 4328 customers of a gambling operator from Finland were randomized to receive a prompt to set a voluntary deposit limit of optional size either 1) at registration, 2) before or 3) after their first deposit, or 4) to an unprompted control condition.

Results: The intervention groups did not differ in either proportion of participants with positive net loss or size of positive net loss. The pooled intervention group did not differ from the control group regarding proportion of gamblers with positive net loss or size of net loss. The intervention groups had higher rates of limit-setters and net loss was highest among participants who had increased/removed a deposit-limit. 

Conclusions: Prompting online gamblers to set a voluntary deposit limit of optional size did not affect subsequent net loss.