Molnupiravir is an antiviral which inhibits viral replication by promoting mutations in the copies of the viral RNA, and has been used in immunocompromised populations. As expected, there are signs that its use accelerates SARS CoV 2 variants.

Molnupiravir promotes G to A mutations as well as to a lesser extent, C to T mutations

The authors conclude "Overall in the dataset, we observe a systematic accelerated evolutionary rate in high G-to-A branches (p<0.001), consistent with the action of a mutagenic drug."

https://www.medrxiv.org/content/10.1101/2023.01.26.23284998v...