How can you define ‘drug’? Nobody really knows

What is a medical drug? Ask someone on the street and they’ll probably tell you it’s what you take when you’re not feeling well.

This understanding is wrong, as we shall see. But after careful investigation, my colleagues and I found that no other potential definition was any better.

Despite their central importance to medicine, we have no idea what medical drugs are. We can’t even tell the difference between drugs and food, let alone drugs and so-called natural alternatives.

Definition of Goldilocks

In a recent article in the Journal of Medicine and Philosophy, my colleagues (Sarah Linton, a pharmacist, and Maureen OMalley, a philosopher of biology) and I attempted to find a viable definition of medicinal drugs.

A viable definition should be broad enough to include anything classified as a drug. To figure this out, we used a drug bank compiled by the Canadian Institutes of Health Research, which lists more than 16,000 substances.

The definition should also be narrow enough to exclude substances that are not normally considered drugs. Take food, for example. Eating a sandwich is usually never considered drug taking.

In short, a viable definition of what drugs are should occupy the Goldilocks zone between these two requirements: large enough to include all drugs, small enough to exclude everything else.

Based on an initial study of pharmacology textbooks, we found three broad ways to define drugs: in terms of what they are, how they work, and what they are used for.

Unfortunately, none of these options fall into the Goldilocks zone.

Are medicines specific chemicals?

If all drugs were a specific type of chemical, then defining drugs would be easy. But this idea is hopeless: there is nothing, chemically speaking, that all drugs have in common.

It’s also tempting to think that drugs are man-made chemicals, made in a lab, while natural supplements come from nature, and that’s the difference.

But many remedies are natural in that sense. Aspirin, for example, is obtained from willow bark.

Read more: Modern medicine has its scientific roots in the Middle Ages how the vulture logic of brain drugs and bloodletting lives on today

This has immediate implications for so-called natural supplements, such as fish oil.

If drugs are chemically indistinguishable from natural supplements, supplements should not be considered a safe alternative. Supplements are no more or less safe than many drugs.

Do drugs perform a specific function?

Perhaps drugs can be defined in terms of what they do. This idea seems promising at first, because many drugs work by binding to receptor molecules in the body.

Think of a lock and key: the receptor molecule is the lock, and the drug is the key that opens it.

The discovery of receptor molecules is significant. For some, this is the big idea of ​​the science of pharmacology.

But this definition of medical drugs is also hopeless. Many drugs do not bind to receptors. Antacids, for example, work simply by changing the level of acidity (pH) in a person’s body.

Read more: Explanation: what is the placebo effect and can doctors prescribe it?

Many placebos also bind to receptors. Placebos are often contrasted with drugs, but defining drugs as things that bind to receptor molecules would include many placebos in the definition. So this definition won’t work either.

Is there a way to define placebos that clearly differentiates them from drugs? This is not obvious, since defining a placebo is also quite difficult.

For example, one might think that placebos are substances that have no therapeutic effect. But placebos can have therapeutic effects (the so-called placebo effect), so this definition won’t work. A number of other definitions face similar problems.

Our research paves the way to explain why it is so difficult to define a placebo. To properly define placebos, we must distinguish them from drugs, which we cannot do without defining what drugs are.

Drugs make me better

This brings us back to wellness. From this point of view, a medical drug is just any chemical substance used in treatment.

This is better: it covers the whole range of substances used as drugs in a medical context.

But now there is absolutely no hope of retaining food and nutrients.

Read more: Poison or medicine? Traditional Chinese Medicine shows that context can make a difference

Consider, for example, total parenteral nutrition. This is a chemical infusion given to people who have trouble absorbing nutrients normally.

Total parenteral nutrition is used in the treatment. But what it does to your body is no different than what a good sandwich does.

Any treatment-based account of drugs inevitably erases the contrast with food.

So what?

In our daily lives, we make decisions that rely on an implicit understanding of what drugs are.

For example, we take paracetamol because it is a medicine. Many of us may also take fish oil precisely because we believe it is not a cure.

Without an account of what the medicines are, we risk making serious mistakes.

We can take substances that we think are inert (placebo) because they are natural (like fish oil), but in fact they are active drugs.

Similarly, all drug legislation assumes that we already know what a drug is.

But we don’t: our understanding is clearly evolving. This means that regulation must also be constantly changing. Therefore, significant resources must be devoted to legislative redrafting as we continue to rethink what medical drugs are, as demonstrated by the recent reclassification of MDMA and psilocybin as drugs in Australia.

Then there’s the food. Food is not given or regulated as medicine in the hospital, with the exception of total parenteral nutrition and similar substances.

But if doctors are using food as medicine to contribute to the well-being of patients, then perhaps it should be subject to the same standards.

This may require a radical rethinking of the way meals are provided in the hospital. Perhaps meals should be administered and regulated with the same care as drugs.

Hospital lunches may never be the same. But that could be good.

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