Metformin will be discussed because of its status as an FDA-approved drug, its lower risk profile (including infection risk) with and without diabetes, evidence suggesting its potential as immunotherapy in the context of infections, and evidence of it ameliorating conditions treated with TNF inhibitors, making it an attractive drug for study (Howlett and Bailey, 1999; Kang et al., 2013; Son et al., 2014; Provinciali et al., 2015; Malik et al., 2018; Routy et al., 2019; Scheen, 2020; Shikuma et al., 2020; Chew et al., 2021; Li et al., 2021; Planas et al., 2021; Samuel et al., 2021). Here, TNF is linked to infection.