This chapter talks about the pharmacology, which includes anticoagulation guidelines. Anticoagulation guidelines are based upon the evidence-based guidelines published by the American Society of Regional Anesthesia and Pain Medicine. If an indwelling catheter is to be placed, refer to anticoagulation guidelines for further guidance on how to plan medication dosing around placement and removal of a catheter. Local anesthetics, steroids, and contrast agents are also discussed in this chapter. A well-illustrated table on anticoagulation guidelines for interventional pain procedures has been provided in this chapter, which is very knowledgeable for students or readers.