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Highlights • tDCS over the dorsolateral prefrontal cortex (DLPFC) has been shown enhance cognitive function. • Main finding was a significant improved of cognitive received active and sham stimulation. • This finding emphasizes the importance of double-blind placebo-controlled experiments in brain stimulation studies. Abstract Transcranial direct current stimulation (tDCS) is a neuromodulation tool that is used widely in many medical/experimental trials. We aim to assess the effect of tDCS over the dorsolateral prefrontal cortex (DLPFC) on cognitive function and obtain safety data in tobacco smokers. In this double-blinded experiment, 22 human subjects (male) were randomized into two groups: active (n = 12), and sham (n = 10) during three consecutive days for 20 min of continuous active versus sham stimulation each day. The cognitive functions outcome variables were the response time (attention switching task [AST]), and the percentage of correct answers (pattern recognition memory [PRM]). Safety data and visual analog scale were obtained before and after each tDCS session. After stimulation, AST showed significant improvement in mean correct latency, congruent and incongruent conditions for active group (p-value = 0.003, 0.004, and 0.005), and sham (p-value = 0.003, 0.004, and 0.003) respectively. In all 66 stimulations, mild itching was observed in 25.6% of cases and burning sensation was observed in 15.9% of cases, in both active and sham groups. While we predicted that performance would only increase during real stimulation, we observed an improvement in performance regardless of whether real or sham stimulation was used. tDCS appeared to be safe, well tolerated, and adhered to the international standard of safety in local population. [ABSTRACT FROM AUTHOR]