See also How to Use section.

Drug interactions may change how your medications work or increase your risk for serious side effects. This document does not contain all possible drug interactions. Keep a list of all the products you use (including prescription/nonprescription drugs and herbal products) and share it with your doctor and pharmacist. Do not start, stop, or change the dosage of any medicines without your doctor's approval.

Warfarin interacts with many prescription, nonprescription, vitamin, and herbal products. This includes medications that are applied to the skin or inside the vagina or rectum. The following interactions listed do not contain all possible drug interactions. The interactions with warfarin usually result in an increase or decrease in the "blood-thinning" (anticoagulant) effect. Your doctor or other health care professional should closely monitor you to prevent serious bleeding or clotting problems. While you are taking warfarin, it is very important to tell your doctor or pharmacist of any changes in medications, vitamins, or herbal products that you are taking.

Some products that may interact with this drug include: imatinib, marijuana (cannabis), dronabinol, mifepristone, other drugs that can cause bleeding/bruising (including "blood thinners" such as apixaban/dabigatran).

Aspirin, aspirin-like drugs (salicylates), and nonsteroidal anti-inflammatory drugs (NSAIDs such as ibuprofen, naproxen, celecoxib) may have effects similar to warfarin. These drugs may increase the risk of bleeding problems if taken during treatment with warfarin. Carefully check all prescription/nonprescription product labels (including drugs applied to the skin such as pain-relieving creams) since the products may contain NSAIDs or salicylates. Talk to your doctor about using a different medication (such as acetaminophen) to treat pain/fever. However, if your doctor has told you to take low-dose aspirin to prevent heart attack or stroke (usually 81-162 milligrams a day), you should keep taking the aspirin unless your doctor tells you not to. Ask your doctor or pharmacist for more details.

This medication may interfere with certain lab tests (such as theophylline levels), possibly causing false test results. Make sure lab personnel and all your doctors know you use this drug.