Words are very important in science. Yes, there is often lots of maths and equations and symbols. There is also diagrams, pictures and graphs. But we need words to name things, to describe them and to tell everyone else about what we have found! The problem with words is there are lots of them and sometimes two different words describe the same thing. Science is full of substances, processes, and theories that have different names. This month’s molecule goes by paracetamol in the UK and acetaminophen in the USA.

I Name Thee… Molecule

Many molecules have several names. This occurs when different people or groups discover the same molecule. The molecule is given different names and both end up being used. Some molecules have old or common names, along with the more technical or correct names.

The Naming Business

More recently, a range of different names are given to drug molecules. These molecules usually have very long and complicated names and so are shortened to make them easier to say.

In addition, drug companies often given drug molecules are much shorter, snappier name when advertising and selling them. As different companies cannot use the same name, then the molecules gain lots of different names.

No Pain, More Than One Name

This month’s molecule is paracetamol, also known as acetaminophen. It is also sold under the brand names Tylenol and Panadol. Calpol, everyone’s favourite medicine as a kid, also contains paracetamol. That’s already a lot of names for one molecule!

Paracetamol is one of the World Health Organization’s List of Essential Medicines. The main use of paracetamol is treat pain and mild fever.

Paracetamol in 20 Atoms

The chemical structure of paracetamol (or acetaminophen!) is shown below:

The chemical structure of paracetamol is shown.

Paracetamol contains a phenol group – a benzene ring with an -OH group attached. On the opposite side of the benzene ring is an amide group – a combination of an -NH group and a -C=O group. The eight carbon, nine hydrogen, one nitrogen and two oxygen atoms form paracetamol.

A World of Names

Paracetamol’s scientific name is actually N-(4-hydroxyphenyl)acetamide, although this is usually shortened to para-acetylaminophenol. We can clearly see the similarity between the name para-acetylaminophenol and both paracetamol and acetaminophen.

A 2-carbon fragment of a molecule may get the name ‘acetyl-‘ something – like acetic acid or vinegar. A group containing a nitrogen with single bonds to hydrogen atoms and carbon atoms only gets the name ‘amino’ – like ammonia and the very smelly trimethylamine. With a ring-shaped molecule like benzene (the hexagonal ring in the two structures above) if groups come off opposite each other they are described as being in the ‘para‘ position. If you’re interested – it goes ortho for ‘next to’, meta for 2 carbons away, and then para. A benzene ring with a simple OH alcohol group on it is called phenol. We’ve discussed phenol before – click here. Those are all the components of both chemical names.

Acetyl-aminophenol becomes acetaminophen. Para-acetyl-amino-alcohol becomes paracetamol. I think you can see the similarities there!

The choice of name depends on the country. The UK and Australia prefer the name paracetamol, while the USA, Japan and Canada use acetaminophen. It’s similar to adrenaline (UK) and epinephrine (USA) – they’re the same thing but have different names that mean the same thing (one from Latin and one from Greek).


Paracetamol is soluble in water as anyone who has dissolved a tablet in a glass of water will know. At room temperature, paracetamol is a white solid and does not melt until 169°C.

A Forgotten Molecule

There is some debate about exactly when paracetamol was first made. Some suggest it was first made in 1856, while other reports suggest it was first made in 1877. However, it was first tested as a medicine in 1887 and sold in 1893.

Unfortunately, paracetamol was not as a popular as another drug and soon the world forgot about this molecule. It was not until fifty years later that the world rediscovered paracetamol.

By the 1950s, scientists had realised that paracetamol was a good drug molecule and had few side affects. Within a decade, paracetamol was on sale in the US, UK, and Australia.

Over the next 70 years the amount of paracetamol bought has grown and grown. In many homes you will find a box of paracetamol tablets.

How It Works

Paracetamol works in nearly the same way as most other painkillers – by interacting with cyclooxygenase enzymes. These cyclooxygenases are often abbreviated to COX1 and COX2 and they pop up in the mechanisms of many other compounds, typically drugs like ibuprofen that act as anti-inflammatory drugs but aren’t steroids (they’re called non-steroidal anti-inflammatory drugs or NSAIDs). COX1 and COX2 are important in the synthesis of a type of molecule we’ve discussed before – prostaglandins – and you can read more about those molecules in this previous post.

Paracetamol gets in and interferes with how these two enzymes would produce these pain-causing prostaglandins and so can reduce or stop pain from happening. Paracetamol is also thought to slightly reduce fever.

Four Steps to Pain Relief

There are several different ways to make paracetamol. Most of these start with the molecule phenol, a benzene ring (the hexagon shape) with a hydroxyl group (-OH) attached to the ring.

The next step is to react with group with nitric acid to form nitrophenol. In this reaction, one of the hydrogen atoms is replaced with a nitrate group (NO2).

From here, the nitrophenol reacts with hydrogen over the metal nickel. This reduces the nitrophenol to aminophenol and involves replacing the NO2 group with an NH2 group.

The final step is to react the aminophenol with acetic anhydride. In this final step, the CH3-C=O group replaces one of the hydrogen atoms bonded to the nitrogen atom.

Medicine Is Only Good In Small Amounts

Paracetamol is a fantastic molecule and a hugely beneficial drug. But, like any drug or medicine, too much is dangerous. Paracetamol overdoses are unfortunately common in countries such as the UK and USA. Overdoses happen when people take more paracetamol then they should over a very short time. Sometimes they are deliberate, but it can be doe accidentally.

The paracetamol molecule itself is not actually toxic – it’s what it gets turned into once inside your body that is. When the dose is low, your body can deal with the toxic side products and remove them from your body. Unfortunately, if a person accidentally takes a larger dose the toxic side products can accumulate and negative side effects can add up.

Paracetamol overdoses are dangerous because they cause sweating, sickness, liver failure and death! There is no pleasant way for anybody to leave this world, but this certainly isn’t one. If you, or anyone you know, might be worried about life and need someone to speak to there are people who can help. Please speak to the Samaritans if you need to.

Keep Away From Animals

Paracetamol is a great drug molecule for humans, but not as good for pets. Paracetamol is safe to give to dogs, but only by a vet. It is very important to keep an eye on the dog as well.

a cartoon of  dog

Definitely do not give it to cats! Paracetamol is toxic to cats!

a cartoon of a cat with two different coloured eyes

Feeling Fine

Science will continue to discover, describe and name new things. Chemists will continue to find and create new drug molecules, and drug companies will continue to sell them. As a result, molecules will continue to have several different names.

However, molecules may have different names, but it is still the same molecule, and will behave in the same way. Paracetamol may go by many names, but it is still a highly popular medicine. For over 70 years, paracetamol has been relieving pain, and will do so for many more years.


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