CYP2C9 and epilepsy syndrome: In summary, this chapter concludes that the personalization of MM therapy should combine three layers: (i) clinical evidence (strongest for CBD in selected epileptic syndromes; moderate for MS spasticity; varied and dynamically growing for chronic pain); (ii) biology and pharmacology (PK/PD differences between routes of administration, involvement of CYP2C9/2C19/3A, and potential sex differences); and (iii) safety and interactions (especially CBD–clobazam and CBD–valproate).