What medication should be recommended for a traveler to prevent diarrhea?

The recommended medication for preventing diarrhea in travelers is loperamide. This medication works by slowing down gut motility, which helps to reduce the frequency of bowel movements and can provide relief from diarrhea. Loperamide is particularly effective in treating acute, nonspecific diarrhea, such as that commonly experienced by travelers, often due to consuming contaminated food or water.

While other options listed may have their uses in different contexts, they do not address the prevention of diarrhea specifically. Omeprazole is a proton pump inhibitor used to reduce stomach acid and treat conditions such as GERD, but it does not have a role in preventing diarrhea. Famotidine, an H2 receptor antagonist, is used to decrease gastric acid secretion and is also not focused on diarrhea prevention. Lubiprostone, a medication primarily used to treat chronic constipation and irritable bowel syndrome with constipation, works by increasing fluid secretion in the intestines and is not indicated for the prevention of travel-related diarrhea. Thus, loperamide stands out as the appropriate choice for this scenario.