A nurse is providing teaching about dietary supplements to a client who has erectile dysfunction and has been prescribed nitroglycerin. Which of the following statements is the most important for the nurse to include in the teaching?

A. "Dietary supplements may be expensive and are not typically covered by insurance.": Cost and lack of insurance coverage are true for many supplements, but this is not the most critical safety point when the client is taking nitrates. B. "Dietary supplements have not been tested and approved by the government.": Dietary supplements are regulated differently than prescription drugs and do not require FDA preapproval for efficacy, but this statement is general and not the most immediate safety concern for a client on nitrates. C. "Dietary supplements can cause a drug-drug interaction with nitrates.": Some over-the-counter “sexual enhancement” or herbal products have been found to contain undeclared PDE-5 inhibitors (for example, sildenafil) or analogs; those hidden ingredients can dangerously interact with nitrates (e.g., nitroglycerin) and cause severe hypotension -this is the most important safety point to emphasize. D. "There is not enough evidence that dietary supplements are effective for erectile dysfunction.": Many supplements lack strong evidence of benefit, but the immediate and potentially life-threatening interaction risk with nitrates is a higher-priority safety concern for this patient.