When I get a cold, I armor up with DayQuil so I can do my job without drowning in mucus. Now my killjoy co-worker says taking cold medicine actually makes you sick longer. Does it? —Brian L.

The theory behind your friend's hot take goes like this: That tide of mucus is your immune response, and when you tamp it down with drugs, it's just going to take that much longer to clear the virus from your system.

Makes sense, right? Unfortunately, no one seems to be sure whether it's actually true—some sources agree with your co-worker, but plenty of others say a cold will run its course in seven to 10 days no matter what you do.

By the way, anyone surveying the dazzling variety of pills, elixirs, hot-drink powders, capsules and syrups on offer in the cough-and-cold aisle might be forgiven for thinking we have a massive pharmacopoeia available for dealing with colds and flu.

Think again. The market is dominated by just six actual drugs, all of which have been available since at least the 1970s: acetaminophen (aka Tylenol), a pain and fever reducer; dextromethorphan, a cough suppressant; phenylephrine, a decongestant; guaifenisin, an expectorant (i.e., a chest-congestion loosener); and doxylamine and diphenhydramine, both antihistamines.

These six medicines, in various combinations, make up the bulk of over-the-counter cold remedies. And since there are only about a half-dozen combinations that make sense, there's a lot of overlap.

For example, TheraFlu Nighttime Severe Cold & Flu powder turns out to be pharmacologically identical to Dimetapp Multi-Symptom Cold & Flu syrup, which in turn is the same as Mucinex Fast Max Nighttime Cold & Flu caplets.

Speaking of Mucinex, it's been 15 years since it first rolled out its anthropomorphic GCI phlegm balls. From the heavy ad buys and the fact that it costs upward of a dollar a pill, I'd always assumed Mucinex was a newly patented breakthrough drug—the Viagra of snot, if you will.

It turns out Mucinex is just plain old guaifenisin. You can buy bottles of the pills at dollar stores. The boys of Madison Avenue somehow parlayed a family of talking loogies into a 5,000 percent markup, and no one's even mad at them. Martin Shkreli, eat your heart out.