May cause hypoglycemia w/ insulin, oral antidiabetics, salicylates & pyrazolones, MAOIs, oxytetracycline, ACE inhibitors, fibrates, cyclophosphamide & derivatives, β-blockers, clonidine, reserpine & guanethidine. Risk of lactic acidosis increased w/ alcohol & cimetidine. May impair absorption of vit B
12. Anticoagulants.