In 2019, the efficacy and safety of biologic therapy offer most patients with psoriasis the opportunity to achieve safe and complete or nearly complete clearance of skin lesions. [1][2][3][4] A major obstacle remains across the world, however, in getting access to the best psoriasis medications, owing to high cost and/or lack of adequate health insurance. Indeed, it is commonplace for insurance companies and national regulatory authorities to control use of biologics to reduce overall costs to health care. More specifically, patients with psoriasis often have to experience treatment failure with cheaper, less effective, and less safe nonbiologic drugs prior to gaining access to biologics. 5 The use of older biologics, such as adalimumab and ustekinumab, is often required (because of their lower cost in some settings) prior to using newer biologics that target interleukin (IL)-17A or IL-23, 5 which are generally more effective. [1][2][3][4] Thus, the cost of health care often dictates therapeutic choices, rather than the physician and/or patient choosing what is best for the patient.Understanding which currently available medications will be most effective for treating a given patient with psoriasis is a practice gap for dermatologists, defining an opportunity for both personalized medicine and potential cost savings to the health care system by avoiding step therapy. While nonbiologic therapeutic options and older biologics for psoriasis are generally less effective than newer biologic options, subsets of patients do well with older therapies. [1][2][3][4] For example, 42.0% to 57.6% of patients with psoriasis taking ustekinumab achieve 90% improvement in their Psoriasis Area and Severity Index (PASI 90) at week 16. 1,2,4 If one could understand and predict which patient will respond to an older, cheaper biologic, such as ustekinumab, higher-cost alternatives could be avoided. In this issue of JAMA Dermatology, Tsakok et al 6 report that higher serum drug levels of ustekinumab soon after initiating therapy can predict whether a given patient will respond in the future to ustekinumab. Therapeutic drug monitoring (TDM) like that described in this article is available for ustekinumab 7 and adalimumab, 8 giving dermatologists tools that can help guide early decision-making on whether to keep treating a patient with a given biologic or to switch to another drug.In Great Britain, patients with psoriasis must cycle through methotrexate, cyclosporine, and phototherapy before being treated with a biologic. 5 After this, adalimumab and ustekinumab have been selected as first-line biologics (as designated in the National Health Service formulary), and must be used by patients prior to being treated with a newer more effective anti-IL-17A or anti-IL-23 biologic. [1][2][3][4][5] Tsakok et al 6 examined British patients with psoriasis who were enrolled in