People believing in conspiracy theories question mainstream thoughts and behavior, but it is unknown whether it is also linked to lower adherence to the prosocial norms of the broader society. Furthermore, interventions targeting correlates of the belief in conspiracy theories so far are scarce. In four preregistered, mixed-design experiments (Ntotal = 1,659, Nobservations = 8,902), we tested whether believing in conspiracy theories is related to lower prosocial norm adherence and whether deliberation about the reason for the norms mitigates this relationship. Across four studies with the U.S. samples, we found that believing in conspiracy theories correlated negatively with prosocial norm adherence in the control condition, which was less pronounced after deliberation (effect size of interaction: d = 0.16). Whether the norm was related to the law or not did not moderate this effect. Results point toward possible ways of mitigating negative correlates and potentially also consequences of believing in conspiracy theories.