Phentermine is a sympathomimetic amine that acts as a central nervous system stimulant, primarily targeting norepinephrine and dopamine neurotransmission. In the context of Cluster Headache treatment, it may help modulate pain perception and reduce the frequency and intensity of attacks by influencing neurological pathways involved in headache pathogenesis. Its off-label use in this condition is based on its potential to alter neurochemical signaling and provide relief through central nervous system effects.