Stating the Blindingly Obvious
So there's a new study that says dextromorphan and diphenhydramine in cough syrup aren't any better for coughs than sugar water.
First off, diphenhydramine is not the sort of stuff you ought to be passing out to kids. For part of the population, it's a non-drowsy antihistamine, yes. But for the rest of the population, it's an extremely strong sedative that will totally knock you out even in small doses and make you confused and dizzy even after you wake up. What the frick are they doing putting this stuff in alcohol-based syrups?!!! It's evil enough in Benadryl!
Second, I coulda told them that Robitussin DM is pretty useless. PE was the stuff, because it broke up the gunk in your chest a bit. (But they stopped selling it. Bah.)
Third, it's not the cough that's the problem, usually. Once you get to that point, you're taking prescription cough syrup and breathing Vicks. The problem is drippage (which causes the cough) and that's not really going to stop until the cold or flu does. The best that decongestants and antihistamines can do is dry you up just a little. But even that little is a godsend when you have a cold.
Fourth, the real active ingredient in cough syrup is alcohol. This ought to be blindingly obvious to everyone. What the heck else is "helping you to sleep"? Ummmm...could it be the depressant? Ooh, concept. The only problem is that alcohol does make you sleep (and thus not cough), but it also wakes you up later. But that's going to happen anyway with a cold or flu, so do you care? Also, alcohol tends to dry out your throat a bit, but you're drinking lots of fluids anyway. The big plus is that alcohol numbs the nerve endings in your mouth and throat temporarily, which...suppresses the coughing reflex. Well, whodathunkit.
(Obviously, when diphenhydramine is acting as a sedative, you also won't be coughing. But given how powerful its effects are on adults, I'd be reeeeeal leery about giving it to a kid. I think we all know more about dosages with alcohol.)
So yes, if your child has a cold, sugar water or a hot drink is probably more effective on a cough than dextromorphan (because it's meant to deal with your head, dummy!). But what you really need to do is take honey, mix it with a little whisky, and turn it into a hot toddy for your kid (assuming your child has no problems with alcohol, of course). Then you've got your active ingredient of alcohol mixed with a soothing syrup and a hot drink, all in one.
Or you could buy cough syrup and get the same thing (bar heat), but be able to give it to your kid without any nasty questions about shot glasses or giving alcohol to a minor or lack of dexterity caused by you yourself being sick. Hmmmmmmm.
Just make sure that syrup doesn't contain diphenhydramine, all right? That'll make me feel better.