See also How to Use section.Your doctor or pharmacist may already be aware of any possible drug interactions and may be monitoring you for them. Do not start, stop, or change the dosage of any medicine before checking with your doctor or pharmacist first.Before using this medication, tell your doctor or pharmacist of all prescription and nonprescription/herbal products you may use, especially of: alpha blockers (e.g., doxazosin), beta blockers (e.g., propranolol, metoprolol), calcium or magnesium sulfate received through a vein, digoxin, fentanyl, melatonin, quinidine, certain drugs that may weaken the immune system (e.g., sirolimus, tacrolimus), drugs affecting liver enzymes that remove nifedipine from your body (e.g., cimetidine, nefazodone, quinupristin/dalfopristin, St. John's wort, azole antifungals such as itraconazole, macrolide antibiotics such as erythromycin, rifamycins such as rifampin, anti-seizure medicines such as carbamazepine/phenytoin).Check the labels on all your medicines (e.g., cough-and-cold products, diet aids, nonsteroidal anti-inflammatory drugs-NSAIDs for pain/fever reduction) because they may contain ingredients that could increase your blood pressure or heart rate (e.g., pseudoephedrine, phenylephrine, chlorpheniramine, diphenhydramine, clemastine, ibuprofen, naproxen). Ask your pharmacist about using those products safely.This document does not contain all possible interactions. Therefore, before using this product, tell your doctor or pharmacist of all the products you use. Keep a list of all your medications with you, and share the list with your doctor and pharmacist.