Devil's claw should not taken with anticoagulant drugs (blood-thinners), such as warfarin (coumadin). Taken together, they may increase the risk of bleeding or cause spontaneous bleeding.
Insulin or Insulin Analogs:
Sulfonylureas helps to treat type 2 diabetes mellitus. One drug in this class, called chlorpropamide, is used as a treatment for diabetes insipidus. Based on one animal study, which found devil's claw extract reduced blood glucose in fasted normal and diabetic animals, sulfonylureas should not be combined with devil's claw unless under the supervision of a qualified health practitioner.
Griffith, H. Winter. Complete Guide to Prescription and Nonprescription Drugs 2006 Edition. New York: Perigree, 2005.
Mahomed IM and Ojewole JA. "Analgesic, antiinflammatory and antidiabetic properties of Harpagophytum procumbens DC (Pedaliaceae) secondary root aqueous extract." Phytotherapy Research. 18.12 (2004):982-9.