Assembly Bill 400 establishes a civil cause of action for minors under 18 who are injured by gender transition procedures performed by health care providers. The bill defines "gender transition procedure" to include medical or surgical services aimed at altering an individual's physical characteristics to align with their perceived gender. It allows minors, or their parents or legal guardians, to sue for damages, including compensatory and punitive damages, if they suffer any physical, psychological, emotional, or physiological injuries from such procedures. Importantly, the bill stipulates that any legal action must be initiated before the individual turns 33 years old.

The bill also outlines specific defenses for health care providers against such lawsuits. These defenses require thorough documentation of the minor's perceived gender over a two-year period, certifications from multiple health care providers regarding the necessity of the procedure for mental health concerns, and the informed consent of both the minor and their parent or guardian. Additionally, the bill mandates that parents and minors receive a detailed notice about the potential risks and consequences of gender transition treatments, including the possibility of worsening conditions and long-term health risks associated with puberty blockers and cross-sex hormones.