How Drugs Work: Cold and Flu Medications

Now, 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.)

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.

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.

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.