Final answer:
Ibuprofen is the over-the-counter medication that can reduce the antihypertensive effects of Captopril, an ACE inhibitor used to treat high blood pressure.
Step-by-step explanation:
Clients on Captopril should be aware that taking nonsteroidal anti-inflammatory drugs (NSAIDs) can reduce the antihypertensive effects of this medication. The over-the-counter medication in question that can interact with Captopril to reduce its effectiveness in treating high blood pressure is ibuprofen. Captopril is part of a class of medications known as angiotensin converting enzyme inhibitors (ACE inhibitors), which are used to lower blood pressure by blocking the conversion of angiotensin I to angiotensin II. Other common over-the-counter pain relievers, such as acetaminophen and aspirin, can also have interactions, but it is ibuprofen that is well-known for diminishing the antihypertensive effects of ACE inhibitors. Lastly, diphenhydramine, an antihistamine, does not have this effect on blood pressure medication.