Tag: therapeutic index

NTI-Specific Substitution Laws: Which States Have Special Rules for Critical Medications

By : Tamsin Riverton
Date : Mar 10 2026

Twenty-seven U.S. states have special rules blocking or restricting generic substitutions for narrow therapeutic index (NTI) drugs like warfarin, levothyroxine, and lithium. Here's where substitution is allowed, restricted, or banned - and what it means for patients.