How Drugs Work: Cold and Flu Medications

This How Drugs Work post is an edited re-share of a previous post; I wanted to share it again because it’s that time of year, again, and my immune system has spent the past week waging war on an icky cold virus, as I’m sure many of yours have. 
I’m the kind of person nerd who doesn’t like to take any medication unless I know what it does and how it works. I think more people should be like this, actually, not just because it’s often super-amazing and cool, but also because it’s good to know what you’re taking, and why. As a general rule in life, it is always better to be informed about what you’re putting into your body (unless it relates to the number of calories in white chocolate cookies, it is definitely better NOT to know that. Ever.)
So, you’re ill. You reach for the cold & flu tablets/drink/sachet. And now you want to know what’s in there? How does it make you feel better? The thing with these remedies is that they mainly treat symptoms. None of them actually attack or destroy the virus that’s making you feel ucky. Instead they alleviate the symptoms, while you lie still and allow your immune system to kick some serious viral butt. All your body really needs, most of the time, is for you to rest while it works. I actually really like this excuse for doing nothing… “Yes, I can see how it looks to YOU like I’ve been watching BBC’s Pride and Prejudice for 5 hours straight but as it happens, I’ve been waging constant battle against pathogenic viruses so I’m very tired and that’s why you should bring me tea now”.
Entirely gratuitous picture of Colin Firth? On this blog?
Never. He’s um… got a cold. He’s here to learn how his Lemsip works.
Getting in the way of your lovely peaceful rest however is the fact that you ache all over, you can’t breathe through your nose and your throat is lined with razor blades.  Even with the distraction of Colin Firth in a wet white shirt, that’s not conducive to comfort. That’s why you take the medicine. And this is what the medicine does…
Wild berry and hot orange. We only do fancy flavoured cold remedies around here.
Active ingredient one: paracetamol
Paracetamol is in nearly all cold and flu remedies, billed as a painkiller and a fever reducer. It’s an incredibly interesting drug, actually, it’s one of those where we thought we knew how it worked, and then it turned out we weren’t entirely right. Initially it was considered to be a non-steroidal anti-inflammatory drug (NSAID). NSAIDs are supposed to act against pain by inhibiting an enzyme, COX-2, which is involved in producing chemicals that cause an inflammatory response (pain, redness, swelling). The same chemicals are also present in the hypothalamus, the internal thermostat of the brain, and are involved in raising body temperature. It seems obvious to assume that paracetamol blocks COX-2 from producing these chemicals and therefore neatly lowers your temperature. And indeed that might well be the case, although no-one is sure.
Last year an article in Nature Communications suggested another way in which paracetamol might kill pain. Once it’s in the body, paracetamol is broken down into smaller chemicals. David Andersson and his colleagues showed that two of these smaller metabolites of paracetamol can block a receptor in the spinal cord. Their theory is that blocking this receptor stops messages of pain being sent from your body, up the spinal cord, to the brain. Of course this doesn’t answer the question of reducing body temperature, but it’s entirely possible that paracetamol acts in more than one way, like a multi-tasking super drug. Either way, it’s certainly a good painkiller, either by reducing inflammation, blocking the transmission of ouchy-messages, or a bit of both.
Active ingredient two: phenylephrine
Phenylephrine is your decongestant, and this time we do know how it works. It binds to a receptor, the alpha-adrenergic receptor, and this causes blood vessels in your nose to contract and get narrower. Obviously this means there is less blood supply to the area, and this helps you feel less bunged up in two ways, first, constricted blood vessels in the mucus producing layer of the nasal passages means less mucus. Second, part of the bunged up feeling comes from swelling in your sinuses, contracting the blood vessels reduces this swelling, so your nasal passages open again, and you can smell your Heinz Tomato Soup (I’m assuming everyone eats Heinz Tomato Soup when they’re ill, no?).
Whilst we know how phenylephrine works, for a while there has been on-going debate about how effective it really is, some studies say that there isn’t enough evidence to prove that it does anything useful, whereas others say there is. In any case, that’s how phenylephrine would work, if indeed it does work.
Active ingredient three: guaifenesin
The third and final ingredient in some cold and flu medicines is guaifenesin. It’s listed in your cold and flu medication as an expectorant, a drug that loosens chesty coughs. However, yet again, the way in which guaifenesin works is… well, basically it’s not at all understood. The general idea is that it reduces the viscosity of the mucus in your airways, making it less gloopy and therefore easier to cough up. However, no-one appears to really know how it does this. On top of this, there are other theories, that it somehow blocks your natural ‘cough reflex’, or that it increases the action of cilia, helping to clear mucus out of the airway faster.  Again, no-one knows how it would do either of those things. Guaifenesin then is something of an international drug of mystery. It’ll help you cough up mucus… but if it told you how, it’d have to kill you.
So, there you have it, the main active ingredients in cold and flu medicines. A complicated and reticent lot, that either work mysteriously or can’t decide whether or not they’re going to work. These are your companions in the fight against viral doom. Or, the things that’ll make you feel vaguely human while your immune system does its thing.  It depends how overdramatic you’re feeling, or whether you’ve got man-flu, which obviously cannot be treated by any methods known to humankind.

8 thoughts on “How Drugs Work: Cold and Flu Medications

  1. Dextromorphan tends to be in cough syrups rather than generic cold and flu medications, or at least it's not in the ones I was thinking of (e.g., Lemsip Max, Beechams All in One). However, it's an incredibly interesting drug, could probably use a whole post on its own. As well as being a cough suppressant, it also has recreational uses as a hallucinogenic drug! In terms of its actual medicinal use, it's not an expectorant like guiafenesin is (theoretically), instead it's known as an anti-tussive, or cough suppressor. Because it has so many mechanisms of action within the nervous system (hence the hallucinogenic side effects at high doses!), it's hard to pinpoint exactly how it works. On top of that, the 'cough centre' of the brain is a fairly poorly defined area, making it even more difficult to isolate the mechanism of action. The basic idea is that it inhibits the cough reflex, either by blocking transmission of the signal along the reflex arc, or altering the threshold for the reflex to kick in in the first place. Further than that, well, it's another elusive little drug of mystery. Clearly cough medicines are highly secretive! K x

  2. When I catch a cold, I prefer to stick to the aspirin and other specific medicines. And, mopreover, I read about aspirin analogue ibuprophen, but I do get rid of the fever with their help only after it is above 38C.

  3. Pingback: Weekly Round-up (Dec 15-21, 2012) | scicommnetwork

  4. Pingback: How Drugs Work: Cold and Flu Medications | Science Communication Blog Network

  5. Mullein is also excellent for producing Cough Syrup, specifically for dry coughs. It possesses a soothing demulcent for the respiratory system. ‘Demulcent’ means a herb wealthy in mucilage that is soothing and in this situation is also delightful!.When you feel the leaves of Mullein they really feel wonderfully soft and silky which is a certain sign that the leaves have mucilage. Mucilage, although it sounds disgusting, is excellent stuff as it coats and protects mucous membranes lining the gut and respiratory system.”

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