Final answer:
Warfarin is the medication that interacts with feverfew, which is used by clients to prevent migraine headaches. This combination can increase the risk of bleeding, necessitating careful monitoring of the patient.
Step-by-step explanation:
The medication that is known to interact with feverfew when taken by a client who has migraine headaches is c. Warfarin. Feverfew may increase the risk of bleeding, especially if taken with other medications that can also increase the risk of bleeding, such as warfarin, a blood thinner. Patients should be monitored for signs of bleeding if they are taking this combination.
None of the other listed medications - a. Acetaminophen (also known as paracetamol), b. Propranolol, or d. Omeprazole - are known to have a significant interaction with feverfew. While feverfew may be used as a preventive measure for headaches, it should be noted that introducing any herbal supplement can have potential interactions with prescription medications.