Hard-won experience? I vaguely remember when Sudafed got put behind counters because it was used to make meth. I don't frequently get sick. Often, the last medication I bought is expired by the time I need it again. One year, I found something that worked for me. Another year, I thought I bought the same thing, but it just didn't work. The one I had originally bought (same brand) had a behind-the-counter version that worked. It's annoying to catch the pharmacy when it's open, but now I just ask the pharmacist for generic Sudafed with the smallest-lasting dose (so I can decide if I want to take more).

I've found with most medications looking for an active ingredient and an amount is helpful. You can search for effectiveness or side-effects. The brand I got last time isn't always available and they'll have 3-hour or 12-hour versions with warnings about exceeding recommended dosages (or mixing medications). Or company annoyingly package similarly-branded things that just aren't the same.