Before taking metformin,tell your doctor and pharmacist if you are allergic to metformin, any of the ingredients of metformin liquid or tablets, or any other medications. Ask your pharmacist or check the manufacturer's patient information for a list of the ingredients.tell your doctor and pharmacist what other prescription and nonprescription medications, vitamins, nutritional supplements, and herbal products you are taking. Be sure to mention any of the following: amiloride (Midamor); angiotensin-converting enzyme (ACE) inhibitors such as benazepril (Lotensin, in Lotrel), captopril, enalapril (Vasotec, in Vaseretic), fosinopril, lisinopril (in Zestoretic), moexipril (Univasc), perindopril (Aceon), quinapril (Accupril), ramipril (Altace), and trandolapril (Mavik); beta-blockers such as atenolol (Tenormin), labetalol (Trandate), metoprolol (Lopressor, Toprol XL), nadolol (Corgard, in Corzide), and propranolol (Hemangeol, Inderal, InnoPran); calcium channel blockers such as amlodipine (Norvasc), diltiazem (Cardizem, Cartia, Diltzac, others), felodipine, isradipine, nicardipine (Cardene), nifedipine (Adalat, Afeditab CR, Procardia), nimodipine (Nymalize), nisoldipine (Sular), and verapamil (Calan, Covera, Verelan, in Tarka); cimetidine (Tagamet); digoxin (Lanoxin); diuretics ('water pills'); furosemide (Lasix); hormone replacement therapy; insulin or other medications for diabetes; isoniazid (Laniazid, in Rifamate, in Rifater); medications for asthma and colds; medications for mental illness and nausea; medications for thyroid disease; morphine (MS Contin, others); niacin; oral contraceptives ('birth control pills'); oral steroids such as dexamethasone, methylprednisolone (Medrol), and prednisone (Rayos); phenytoin (Dilantin, Phenytek); procainamide; quinidine (in Nuedexta); quinine; ranitidine (Zantac); triamterene (Dyrenium, in Maxzide, others); trimethoprim (Primsol); or vancomycin (Vancocin). Your doctor may need to change the doses of your medications or monitor you carefully for side effects.tell your doctor if you have or have ever had any medical condition, especially those mentioned in the IMPORTANT WARNING section.tell your doctor if you are pregnant, plan to become pregnant, or are breastfeeding. If you become pregnant while taking metformin, call your doctor.tell your doctor if you eat less or exercise more than usual. This can affect your blood sugar. Your doctor will give you instructions if this happens.