State Laws and Generic Substitution in the Year After New Generic Competition

Substitution of brand-name drugs with less expensive, equally effective interchangeable generics is an important strategy for promoting adherence and controlling prescription drug spending. US state laws govern generic substitution, but there is variability among states in how these laws are designed. We aimed to determine how different features of state laws regulating generic substitution are associated with use of generic drugs.

Using national claims databases, we studied individuals with commercial insurance or Medicare Advantage plans who newly initiated one of 34 prescription drugs during the year after new generic competition (2017-2018) to determine any association between generic use and 3 different features of state laws. We used multivariable logistic regression to adjust for demographic and clinical characteristics.

Of 502 763 individuals who initiated one of the drugs, 409 856 (81.6%) received a generic version. Those in states requiring patient consent or notification had lower use of generics (81.1% vs 82.9%; adjusted odds ratio 0.89; 95% confidence interval 0.87-0.91; P < .001). By contrast, mandating versus permitting generic substitution and protecting pharmacists from liability did not appear to have significant effects.

In this study of commercially insured and Medicare Advantage patients, patients in states requiring consent or notification for pharmacists to substitute Food and Drug Administration-certified interchangeable generics had lower use of generics. Laws in 39 states plus the District of Columbia could be amended to improve use of inexpensive and equally effective generic drugs.