The most important hypothesis of this research was based on the fact that the mechanism of the effect of omega-3 on depression and obesity is formed through its accumulation in the dorsolateral prefrontal cortex (DLPFC), especially in women. Accordingly, we investigated the omega-3 intake and the concurrent stimulation of the DLPFC by tDCS and hypothesized that the synergy of these two treatments can increase the obtained effect size in patients with depression and overweight. This research was a double-blind randomized controlled trial (RCT) with a factorial design consisting of four treatment and control groups. The participants were females with depression and overweight on an outpatient basis. They received 5 ml/day omega-3 syrup (545 mg DHA, 620 mg EPA) or placebo adjunct with 12 sessions sham/tDCS stimulation administered for 3 weeks with anode-left/cathode-right protocol in the prefrontal cortex (1.5 mA, 15 minutes' stimulation / 15-20 minutes' rest intervals/one visit per week, 4 stimulations per visit). tDCS or omega-3 alone did not significantly improve the executive functions, depression, food cravings, and weight in the experimental groups compared to the control group (P > 0.05). However, tDCS adjunct with the omega-3 had a significant and positive effect on improving weight change (P = 0.011; df = 1; F = 1.27; Eta = 0.108) with a power of 0.73 compared to the control group. Furthermore, their interaction led to an improving trend in executive functions and a decreasing trend in food cravings which are clinically important. tDCS could strengthen the omega-3 mechanisms of effect through stimulating its accumulation site in the brain (i.e., the DLPFC) and the synergistic effects of these two treatments result in weight control as well as an improvement trend in the executive functions and food craving in women.