Reduced effect w/ epinephrine, chlorpromazine, corticosteroids, OCs, thiazides & thyroid hormone. Reduced hypoglycemic effect w/ rifampicin. Hypoglycemic effect may be heightened by ACE inhibitors, alcohol, allopurinol, selected analgesics eg, phenylbutazone & salicylates, ketoconazole, fluconazole & miconazole, chloramphenicol, cimetidine, clofibrate, coumarins, fluoroquinolones, heparin, MAOIs, ranitidine, sulphonamides, tetracyclines & TCAs. May increase effect & mask typical sympathetic warning signs w/ β-blockers.