This systematic review and dose-response meta-analysis examines the optimal stimulation parameters for transcranial magnetic stimulation (TMS) and transcranial direct current stimulation (tDCS) across various mental disorders. The study included 110 randomized clinical trials involving 4,820 participants, focusing on schizophrenia, depression, obsessive-compulsive disorder (OCD), and substance use disorder. The main outcomes were the near-maximal effective doses of total pulses for TMS and total current dose for tDCS. Significant dose-response associations were observed for schizophrenia, depression, OCD, and substance use disorder, with distinct curve shapes. Bell-shaped curves were noted for schizophrenia (high-frequency TMS on the left dorsolateral prefrontal cortex [LD-LPFC] for negative symptoms and TMS on the left temporoparietal junction for resistant hallucinations), depression (high-frequency LD-LPFC TMS), treatment-resistant depression (LDLPFC tDCS), and substance use disorder (LDLPFC tDCS). Ascending or plateaued curves were observed for depression (low-frequency TMS on the right DLPFC), treatment-resistant depression (low-frequency TMS on the bilateral DLPFC), OCD (low-frequency TMS on the right DLPFC and orbitofrontal cortex), and posttraumatic stress disorder (low-frequency TMS on the right DLPFC). Sensitivity analyses confirmed the main findings. The study highlights the need for further research to refine dose-response models and explore the mechanisms underlying the observed dose-response associations.This systematic review and dose-response meta-analysis examines the optimal stimulation parameters for transcranial magnetic stimulation (TMS) and transcranial direct current stimulation (tDCS) across various mental disorders. The study included 110 randomized clinical trials involving 4,820 participants, focusing on schizophrenia, depression, obsessive-compulsive disorder (OCD), and substance use disorder. The main outcomes were the near-maximal effective doses of total pulses for TMS and total current dose for tDCS. Significant dose-response associations were observed for schizophrenia, depression, OCD, and substance use disorder, with distinct curve shapes. Bell-shaped curves were noted for schizophrenia (high-frequency TMS on the left dorsolateral prefrontal cortex [LD-LPFC] for negative symptoms and TMS on the left temporoparietal junction for resistant hallucinations), depression (high-frequency LD-LPFC TMS), treatment-resistant depression (LDLPFC tDCS), and substance use disorder (LDLPFC tDCS). Ascending or plateaued curves were observed for depression (low-frequency TMS on the right DLPFC), treatment-resistant depression (low-frequency TMS on the bilateral DLPFC), OCD (low-frequency TMS on the right DLPFC and orbitofrontal cortex), and posttraumatic stress disorder (low-frequency TMS on the right DLPFC). Sensitivity analyses confirmed the main findings. The study highlights the need for further research to refine dose-response models and explore the mechanisms underlying the observed dose-response associations.