Two different Janus kinase (JAK) inhibitors-baricitinib and tofacitinib-are 
effective and licensed in active rheumatoid arthritis (RA). There have been 
recent concerns about potential thromboembolic risks with these drugs. Concerns 
about baricitinib focus on clinical trial findings. Using all publically 
available data, we estimate thromboembolic risks are approximately five events 
per 1000 patient years with 4 mg baricitinib daily. Concerns about tofacitinib 
have been raised by analyses of the Federal Drug Administration Adverse Event 
Reporting System (FAERs). These show some evidence of increased risks of 
pulmonary thrombosis, though not pulmonary embolism or venous thrombosis. 
Observational studies suggest in the general population and non-RA controls 
there are one to four thromboembolic events per 1000 patient years. In RA, 
thromboembolic risks increase to three to seven per 1000 patient years. The 
impact of biologics and disease-modifying anti-rheumatic drugs (DMARDs) on 
disease risk appears minimal, and the number of thromboembolic events is between 
four and eight per 1000 patient years. In the short term, full details of 
thromboembolic events in trials of JAK inhibitors need to be published. As the 
numbers of thromboembolic events will be small and patients enrolled in trials 
are not representative of all RA patients who may receive JAK inhibitors, this 
information is unlikely to provide definitive answers. Consequently, in the 
longer term, large observational studies are needed to accurately quantify 
thromboembolic risks attributable to JAK inhibitors and other drugs used to 
treat RA, and differentiate these from risks attributable to RA itself and its 
comorbidities.