Improving access to appropriate mental health and substance use disorder services.

SB 5477 updates Washington's mental health parity law to improve access to mental health and substance use disorder services by requiring health insurers to cover medically necessary care based on established clinical standards. The bill defines "medically necessary" care as services aligned with evidence-based guidelines from recognized medical associations and eliminates previous exclusions for substance use disorder treatments (effective 2026) and certain diagnostic codes. It mandates consistent coverage rules for both mental health and substance use disorders, removes administrative barriers for providers joining insurance networks, and repeals outdated provisions that limited coverage. This directly affects health insurers, healthcare providers, and patients seeking covered mental health and substance use treatment services in Washington.