Lennox-Gastaut syndrome (LGS) is a severe developmental and epileptic encephalopathy marked by drug-resistant seizures and profound cognitive and behavioral impairments, with nearly 95% of individuals affected by moderate to severe intellectual disability. This review comprehensively explores the cognitive and behavioral impacts of current treatment options for LGS, including antiseizure medications (ASMs), neuromodulation strategies, the ketogenic diet, and surgical interventions. Given the limited availability of LGS-specific data for several ASMs, the evidence base is supplemented with findings from general epilepsy populations and individuals with epilepsy and intellectual disabilities. The evidence reveals that ASMs exert varied cognitive and behavioral effects in LGS. Medications such as valproate, lamotrigine, cannabidiol, fenfluramine, levetiracetam, brivaracetam, felbamate, and rufinamide generally support cognitive stability, while topiramate and zonisamide are associated with cognitive challenges. Behavioral outcomes also vary: stability is observed with valproate, lamotrigine, rufinamide, cannabidiol, and fenfluramine, whereas medications like levetiracetam, perampanel, brivaracetam, clobazam, and zonisamide can increase aggression or irritability. Nonpharmacological therapies, particularly when they reduce seizure frequency, typically provide greater cognitive and behavioral stability, with some offering improvement. Early intervention-especially through surgical options-appears most beneficial for preserving cognitive function. Additionally, therapies such as the ketogenic diet and neuromodulation may provide independent cognitive benefits beyond seizure control. This review emphasizes the importance of personalized treatment strategies, integrating cognitive and behavioral evaluations in therapy selection. Key components include baseline cognitive and behavioral assessments, followed by regular follow-up evaluations, particularly after therapy changes. Consideration of minimizing ASM polytherapy, careful evaluation of drug-drug interactions, pharmacogenomic implications, and the need for therapeutic drug monitoring in cases of cognitive adverse effects is essential. Future research should focus on developing assessment tools tailored to the unique needs of individuals with LGS, utilizing connectivity measures to assess intervention impacts, and advancing precision therapeutics to improve cognitive and behavioral outcomes.