What are drugs?

What makes a substance a drug, and why are only some illegal?
15 August 2016

Interview with 

Dr Suzi Gage, University of Bristol


What actually makes a chemical substance qualify as a drug, and why are someAn assortment of drugs legal and others banned? Connie Orbach asked drug researcher and presenter of the podcast "Say why to drugs" Dr Suzi Gage to take her through the basics...

Suzi - The World Health Organisation defines psychoactive substances as substances that affect mental processes, for example, cognition or affect, so they affect your ability to think or your mood.

Connie - How about legal drugs? There's lots and lots of legal drugs which, I'm assuming, affect your brain, things for depression and anxiety, where do they fit into all of of this?

Suzi - Well, there are plenty of legal drugs that are used recreationally, so tobacco, alcohol and caffeine, they're all psychoactive substances. They're all legal although regulated to a certain extent, perhaps not caffeine, but certainly alcohol and cigarettes, but they do have these psychoactive effects as well.

Connie - When we're talking about the difference between legal and recreational drugs it's based on policy and where a line falls?

Suzi - Oh, in terms of the legality - yes, it's partly evidence based as a lot of it's to do with the history in the particular country. So like certain drugs are legal in some countries and not legal in other countries, for example. It's not as simple as saying these drugs are legal because of this and these drugs are illegal because of that. The sort of blurring of the boundaries makes it really quite a difficult things to quantify.

Connie - And when thinking of harm or possible good as well, that's not necessarily as fine a line of: these one are legal and they will do you good and these ones are illegal and they will do you harm?

Suzi - Yes, absolutely. I mean two substances that are the most harmful at a population level in the UK are, most certainly, tobacco and alcohol. And this may be because they're legal and much more widely used than some other recreational substances, but it could also be, and it certainly seems like it might be, that they they are particularly dangerous.

Connie - So that's really surprising when we think about how I might come across drugs I would just be like well, I'm allowed that one, it can't be that bad for me.

Suzi - Absolutely! It's very misleading for someone trying to make informed choices about what they put into themselves.

Connie - Yes. And when we talk about informed choices and what they put into themselves, how do some of these drugs, specifically the illegal recreational drugs, how are they working in the brain? Are they all doing the same thing?

Suze - No, they're definitely not all doing the same thing. There are lots of different types of recreational drugs. So some are stimulants and they'll increase the bodily function, so they'll raise heart rate, they'll raise blood pressure, they might speed up metabolism, that sort of thing. Some are depressants and so have the opposite effect, or analgesics have a sort of pain killing effect. Some are psychedelics, some have a kind of perception altering effect. And so they all work on the brain in different ways but, for the most part, this is due to their impact on neurotransmitters in the brain, so the things that get messages between neurons. And there are various different neurotransmitters and neurotransmitter circuits in the brain and so some drugs will affect some of them and some will affect others. Some will augment the processes of neurotransmission, some will inhibit the processes of neutotrasnission. So they all have quite different effects but, ultimately, they're all affecting, for the most part, these neurotransmitters.

Connie - So these neurotransmitters act as messengers carrying information from one brain cell, or neuron, to the next, and when they get there they match up with their complementary receptor, a bit like pieces of a puzzle. But what's really interesting here is that drug molecules can hijack the system and pretend to be natural neurotransmitters. This works because many of them just happen to be the perfect shape to fit with specific receptors...

Suzi - We have a system in the brain called the endocannabinoid system and, surprising, enough, certain sort of molecules or substances in cannabis, by entering the endocannabinoid system - who'd have thought. Why we developed this in our brains is maybe up for debate, but we've got nicotine receptors in our brain, opioids and that kind of thing, these are systems that are in our brain already.

Connie - How certain drugs came to fit so perfectly with receptors in our brain is, certainly, a bit of a puzzle. We do produce natural molecules that also fit to these receptors, so some people have put it down to coincidence, but there are also theories that maybe something else was going on.

Suzi - Well, it's certainly the case that humans have been using drugs for an extremely long time, or certainly the historical evidence seems to back that up as well as the suggestion that our brains seem particularly able to respond to these kinds of substances, and you can see evolutionarily why it might be advantages. Like if you were chewing on a leaf and it just helps you concentrate that little bit more, maybe you're more likely to have a successful and hunt and you're more likely to eat that night.


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