Antisense RNA is a single-stranded RNA that is complementary to messenger RNA (mRNA) and inhibits its translation. Historically, antisense RNA effects were confused with RNA interference, which involves small interfering RNAs targeting mRNA for degradation. Antisense RNA works by forming duplexes with mRNA, blocking the ribosome from accessing nucleotides or leading to degradation. Examples include transgenic Flavr Savr tomatoes with reduced ethylene production using antisense RNA against an ethylene-producing enzyme, and natural antisense RNA in mice and humans that blocks insulin-like growth factor 2 receptor mRNA. While promising, antisense RNA drugs still face challenges in design, activity, and delivery that have limited