Previously we had a look at the so called opiate drugs, and how they work their lovely painkilling magic on the body. Of course, like every drug, there is a side effect. In the case of the opiates these side effects can actually be pretty mega, which is why so few of them are available over-the-counter, and why some of them are only available over-the-street-corner (…or wherever one goes to buy illegal drugs, that might have been a snappier sentence if I wasn’t so blatantly, but of course endearingly, naive). To start then with the illegal-type traits, opiate drugs are known to cause euphoria. Sometimes, of course, this isn’t a side effect, in fact it’s pretty much exactly what the drug user was going for, particularly in the case of opium itself, and of course heroin. Euphoria is caused by opiate drugs binding to the µ-receptor that we mentioned last time, which causes a reduction in the control of some neurons that are usually controlled by g-amino butyric acid (GABA). This loss of GABA-mediated control results in the release of chemical known as dopamine, which, if you haven’t heard of it before, basically makes you feel nice. It’s the body’s way of rewarding you when you do something it likes, like feeding it cake, or in some people’s case, heroin. Personally, I much prefer cake, and as a bonus it’s far cheaper and easier to get hold of.
On the other hand, in the kind of bemusing and slightly counter-intuitive twist that makes science so freaking wonderful sometimes, some opiates actually cause dysphoria. Dysphoria is the opposite of euphoria, so basically a fancy word for feeling somewhat negative (go on use it next time you have that Monday feeling “how are you?” “I’m a bit dysphoric, frankly”). Some opiates do this by binding not to the µ-receptor but rather to the k-opiod receptor. It isn’t truly understood what happens once the k-receptor is bound and how this causes dysphoria, although some studies have suggested a role for a protein known as p38 in the process (that stands for protein 38, an astonishing piece of creative nomenclature, there). It would be extremely interesting to find out how the k-receptor may trigger dysphoria though, because actually the k-receptor can act in the same way as the µ-receptor in terms of pain relief, and aside from the dysphoria, it has a much shorter list of side effects, and they aren’t as scary either. If it were possible to design drugs that only bound the k-receptor but didn’t cause us all to become depressed, then we may have effective painkillers, without some of the more serious side effects associated with morphine and its pals.
So, onto those serious side effects: well, the most serious is respiratory depression. Respiratory depression (or hypoventilation) is your body failing to sufficiently ventilate the lungs, so your breathing rate is low and your body isn’t getting enough oxygen, or getting rid of enough carbon dioxide. It’s reasonably obvious, I hope, why this is a problem, breathing tends to be reeeally important in life, it’s not one of those take it or leave it activities. Opioid-mediated respiratory depression is caused by the respiratory centre in the brain becoming less sensitive to PCO2 which is the measure of carbon dioxide in the blood that usually lets the body know when you need to breathe more or less to get the right balance of oxygen and carbon dioxide into your blood and to your various body bits. With the sensitivity decreased, the body doesn’t get the messages to breathe more and therefore it just… doesn’t, leading to respiratory depression. Unlike some other drugs, morphine and some other opiates can cause respiratory depression when they’re given at the dosages required to kill pain. This is only the case with the stronger opiates though, not over-the-counters like codeine, and even in the case of morphine the body does, after a while, learn to tolerate the drug, and adapts to avoid the not enough breathing problem.
The final side effect I’m going to mention is one of the most well-known effects of some opiate drugs; addiction, or physical dependence. It’s quite important to note that we’re talking about physical addiction, meaning that your body suffers unpleasant physical withdrawal symptoms if you stop taking them. Heroin is a prime example; stopping taking heroin after a period of taking it causes a range of symptoms that feel rather like flu, but worse. These symptoms will pass, if you can stick them out, but that’s way easier to type than to do. The precise reasons for physical addiction are again not fully understood, but there is some information. It is known that neurons from certain area of your brain (including a bit known as the locus ceruleus) send fewer messages while there are opioids in your system, and starts to send a lot more messages once the drug is gone (I’m envisaging this as something along the lines of Jack Sparrow “why is the heroin gone?!”, which is somewhat inaccurate). It is possible that these messages are responsible for some of the symptoms experienced by addicts going “cold turkey”
So, that was our whistle-stop tour of the nasty side of the opiates. Unfortunately it’s too huge a topic to have been done entirely comprehensively so if there’s anything you’d like to understand further, please please let me know. As ever, any comments, requests or general feedback could not be more welcome.