The past decade has witnessed an explosion in trial data on JAK inhibitors 
(JAKi). These small molecules target the Janus kinase - signal transducer and 
activator of transcription (JAK-STAT) pathway, blocking crucial cytokines across 
a septum of rheumatic diseases. As a class, JAKi are beginning to demonstrate 
efficacy on par, if not superior to biologics. Two first generation JAKi are 
licensed for use in inflammatory arthritis; tofacitinib and baricitinib. 
Next-generation JAKi have been designed with selective affinity for one JAK 
enzymes, the aim to reduce unwanted adverse effects without declining clinical 
efficacy. Emerging data with selective JAK1 inhibitors upadacitinib and 
filgotinib looks very promising. Despite differences in selectivity between 
JAKi, an overlap exists in their safety profiles. Across the class, a 
characteristic safety signal is emerging with viral opportunistic infections, 
particularly herpes zoster. Post marketing drug surveillance will be essential 
in evaluating the long-term risk with these agents.