The use of peripheral hormones—notably glucocorticoids and other adrenal hormones, growth hormone (GH), insulin-like growth hormone-1 (IGF-1), thyroid hormones, and a combination of these hormones—have been trialed to improve outcomes in prolonged critical illness as well as in ME/CFS and fibromyalgia with varied successes as described below. This evidence concerns the gene TG and myalgic encephalomeyelitis/chronic fatigue syndrome.