SSRIs (Selective Serotonin Reuptake Inhibitors) are not a primary treatment for Cluster Headache but may be used adjunctively to modulate serotonergic neurotransmission and potentially reduce headache frequency. Their mechanism involves inhibiting serotonin reuptake, which can potentially influence neurogenic inflammation and pain perception in the trigeminal system, though their efficacy in Cluster Headache is limited compared to other treatments.