Modern behavioral therapies have claimed that thought stopping is an ineffective technique. This study compares the effectiveness of thought stopping and cognitive defusion on self-reported discomfort and the ability to deal with negative thoughts. 60 participants were randomly assigned to three groups: thought stopping, cognitive defusion and control group. Results from our study indicate that both techniques significantly reduced self-reported discomfort compared to the control group and there were significant differences between techniques in self-perceived ability to deal with thoughts and in self-perceived usefulness, with better results for thought stopping. Our results support that thought stopping, if properly trained, is at least as efficient as cognitive defusion. The authors discuss the mechanisms underlying both techniques and highlight the relevance of functional analysis to select the techniques to be applied to deal with negative thoughts.