Feline infectious peritonitis (FIP) is a devastating disease that was fatal in the past until medical breakthroughs allowed for treatment options. The most commonly used medicine for FIP is GS-441524, but there is another medication, molnupiravir, that has been found to be 77% effective in treating FIP in cats. A clinical trial at Colorado State University found that 73 cats with naturally occurring FIP participated in the study, receiving treatment twice daily for 12 weeks and regularly for six months. The side effects of molnupsirivir included constipation, diarrhea, hypersalivation, nausea, vomiting, reduced appetite, pruritus, folded ears, elevated ALT, and neutropenia. This discovery means veterinarians can now treat cats who fail to respond to GS or stop responding to it, or relapse.