**Antisense therapy** is a form of treatment that uses [antisense oligonucleotides](https://en.wikipedia.org/wiki/Antisense_oligonucleotide "Antisense oligonucleotide") (ASOs) to target [messenger RNA](https://en.wikipedia.org/wiki/Messenger_RNA "Messenger RNA") (mRNA). ASOs are capable of altering mRNA expression through a variety of mechanisms, including [ribonuclease H](https://en.wikipedia.org/wiki/Ribonuclease_H "Ribonuclease H") mediated decay of the pre-mRNA, direct steric blockage, and [exon](https://en.wikipedia.org/wiki/Exon "Exon") content modulation through [splicing](https://en.wikipedia.org/wiki/Splicing_(genetics) "Splicing (genetics)") site binding on pre-mRNA. Several ASOs have been approved in the United States, the European Union, and elsewhere.