In summary, it can be stated that the pharmacogenetics of MM is entering a stage of clinical maturity in three areas: (1) safety and exposure—CYP2C9 (THC) and CYP2C19 (CBD–clobazam interaction); (2) neuropsychiatric risk—AKT1 as a moderately strong modifier of individual susceptibility; (3) analgesic efficacy—preliminary but promising multigene signals (ABCB1/TRPV1/UGT2B7). This evidence concerns the gene ABCB1 and Miyoshi myopathy.