Which of the following is true about the onset of heartburn relief when using antacids?

Antacids are designed to neutralize stomach acid quickly, providing immediate relief from heartburn and indigestion symptoms. Since they act directly in the stomach to raise the pH level and alleviate discomfort almost instantly, individuals typically feel a prompt response, making them a preferred option for rapid symptom management. This characteristic makes option A the most accurate description of how antacids function.

Other options are less applicable; for instance, antacids do not require hours to achieve their effect, as they are formulated for rapid action. They can be over-the-counter medications and do not rely solely on prescriptions for effectiveness. Lastly, while food can influence certain medications and substances, antacids are often effective whether taken with or without food, but their immediate nature is not necessarily enhanced by concurrent food consumption.