You can tell a lot about a person by what in their medicine cabinet. A quick peek during a trip to the bathroom and the nosy neighbor could find out whose taking anti-depressants or birth control pills. Maybe someone is being treated for heart disease or bipolar disorder. Or perhaps someone is taking antibiotics for any number of conditions, from a sinus infection to an STD. Certain medicines, if you know what to look for, are a clear sign that someone is undergoing treatment for cancer or HIV.
Of course, most of keep to ourselves what medications we're taking. That's why they're behind the medicine cabinet door, and not lined up on the kitchen counter. Most of us don't go snooping in other people's medicine cabinets. (Do we?) And if we did, the worst we could do with the information is use it to spread gossip.
That is, unless we're in the business of looking into other people's medicine cabinets, or using the information obtained by those who are poking around in the nation's medicine cabinets..