From paracetamol to antibiotics: The secret side effects of over-the-counter medications

From paracetamol to heartburn pills and antibiotics, evidence shows that common – often over-the-counter – medications may have side effects that could alter who you are. Libby Galvin investigates.

Dr Sarah E Hill had only been taking antihistamines for a day when she had an overwhelming panic attack. And the waves of stomach-churning worry kept coming. Dr Hill had another panic attack the next day, and the next. But she didn’t think the pills could be to blame; antihistamines are used to treat allergies and their most common side effect is drowsiness.

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Kaat Zoetekouw/Stocksy United

After three days of feeling constantly on edge, Dr Hill binned the tablets. That day, she says, ‘I was back to normal. I couldn’t believe I hadn’t thought of it sooner.’ As it turns out, one of the lesser known side effects of some antihistamines is agitation.

Understanding how pills can alter our personality is part of her work. An evolutionary social psychologist, Dr Hill is the author of How the Pill Changes Everything: Your Brain on Birth Control, which explores how the contraceptive pill has the potential to alter the fabric of who we are, influencing everything from how we spend our leisure time to who we find attractive.

Dr Hill has even heard from a handful of women who think contraception didn’t change just their attitude to their partner – it changed their sexual orientation altogether. ‘One woman had been on the pill since she was 14 after she was prescribed it to help ease heavy periods,’ she says. ‘All through her late teens and early adulthood she identified as a lesbian and was in relationships with women. Age 23, after nine years, she stopped taking it. Suddenly, she found herself attracted to men – and now she is in a relationship with a man.’

The idea that medication can alter something as central to our personalities as our sexuality ‘raises so many questions about psychology, attraction, even the whole notion of the self,’ says Dr Hill.

While these examples are extreme, most of us are familiar with the idea that hormonal medications can affect us mentally. We all know someone who lost their joie de vivre on the pill, or who found that hormone replacement therapy (HRT) made them fly off the rails rather than help them steady the emotional rollercoaster of the menopause. It’s no surprise either that psychiatric drugs such as antidepressants – which have effects on the chemical composition of the brain – might have other psychological side effects.

But as Dr Hill’s experience with antihistamines shows, it is not just hormones or medications for mental illness that can change how we think and feel.

One in ten people in the UK over the age of 65 takes eight different medications each week, and studies show that the more you take the more likely they may be to change your mood. A 2018 study looking at more than 200 medications with potentially mood-altering side effects showed that 15 per cent of adults who took three or more of them experienced depression.

Among the medications that we are discovering have the potential to change our minds and moods are asthma treatments, heartburn pills, antibiotics, statins and even the common painkiller found in most people’s homes – paracetamol.

An estimated 6,300 tons of paracetamol are sold in the UK every year – that’s 70 tablets
for each of us. But could taking this for a sore head really end up reducing our ability to empathise with others?

Last year, a study in the journal Frontiers in Psychology observed that paracetamol reduced feelings of empathy or shared joy in response to happiness experienced by other people. That this sense of compassion can be blunted is a cause for concern, says Dominik Mischkowski, the psychologist who led the research at Ohio University. ‘That feeling of joy in somebody else’s successes is very important – it’s a driver for building relationships, for building intimacy and closeness.’

These changes play out in real life as well as in the laboratory. ‘I get a lot of emails saying, “I’ve been taking [paracetamol] for a long time, and I feel I have these emotional impairments too,”’ says Dominik.

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Adam Voorhes/Gallery Stock

In fact, when I mentioned this to a family member, they confided that they had noticed a slight ‘hardening’ in themselves since starting to take the painkiller frequently. ‘I have always been a bit of a softie – I’ll often have a lump in my throat or choke back a tear at the end of a sad film, while the rest of the family sit there dry-eyed,’ they explain.

‘But in the past few months I’ve noticed I’m not feeling that way in response to things I know normally bother me. Just the other night we were watching a film about a tragic love affair during the war. My other half was blubbing away, yet it didn’t really affect me.’

The findings are not extreme; there is no suggestion that you might change from a good citizen to a psychopath with the pop of a pill. Yet there is no mention of emotional changes on the warning leaflet that comes with your pharmacy packet of painkillers.

Why not? Often, it’s because doctors don’t want to hear about it. Dr Beatrice Golomb, a professor of internal medicine at the University of California San Diego, has seen the pharmaceutical industry’s reluctance to address behavioural side effects at close quarters in her work on statins.

Statins, which are used by as many as eight million adults in the UK to lower cholesterol and the risk of heart disease, can increase aggression – and not just a little, says Dr Golomb. She’s seen patients turn from kind men to ‘maniacs’ overnight. Although the most acute changes seem to occur in men, her research shows postmenopausal women taking statins are more likely to display increased levels of aggression.

‘Most striking for me was the man who told me that he developed severe road rage to the extent that his family decided that only his wife would drive. But then he would still suffer rage when she drove, shouting and screaming to the point where they’d have to turn around and go home. His wife would have to leave him alone in a room for a couple of hours to calm down because she was concerned for her safety. One day, they both decided it seemed as though this behaviour began when he enrolled in a clinical trial on statins.’

It gets even more frightening. The couple went to talk to the trial investigators who flat out denied a link and said the man had to remain on the trial. ‘But,’ says Dr Golomb, ‘the man swore and stormed out, and when they got home, he stopped taking the statins. Within two weeks he was completely back to normal.

‘The investigator was not just reluctant to listen, he was adamant that this man’s behaviour couldn’t be related to the statins. But on what basis?’

Dr Golomb is clearly exasperated by this closed-mindedness: ‘I think medical training creates a set of attitudes that are reluctant to acknowledge any adverse effects that a doctor hasn’t heard a lot about – even more so in the case of things such as personality change, where doctors are really unfamiliar with the idea.’

It is on us, then – the consumer, the patient – to take the lead and develop a healthy scepticism and a curiosity when it comes to the drugs we buy or are prescribed.

‘Looking at the history of determining whether a medicine causes harm, it usually starts with case reports [a detailed record of the symptoms, diagnosis and treatment of a patient]. If there are enough of them, medicine and drug companies slowly start to take note,’ says Dr Golomb. In Britain this is where the Medicine and Healthcare Regulatory Authority’s Yellow Card scheme is essential (yellowcard.mhra.gov.uk). Anyone can use this website to report any side effect of any medication.

In fact, the reason we haven’t realised the impact of these medicines on our moods sooner comes down to a misunderstanding of the umbrella term ‘side effect’. ‘There is really no such thing,’ explains Dr Sarah Hill. ‘All of a medication’s actions are its effects. We just call things side effects when they are not the reason that we chose to take the medication.’

This is especially true of the pill and paracetamol. These drugs have a ‘butterfly effect’ – taking them to suppress fertility or pain sets off a cascade of other changes, which are different for each of us.

Geoff Durso, a psychologist whose 2015 study showed paracetamol blunts both positive and negative emotions, says he and his colleagues call it a ‘messy drug’, while Dominik Mischkowski describes it as having ‘a shotgun effect’.

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Getty Images

‘Paracetamol crosses the blood-brain barrier and affects brain activity,’ says Geoff Durso. ‘It’s available over the counter because it has mild effects and they’re reliable, but we actually don’t have a great grasp of the critical mechanisms by which it acts in order to relieve pain. It’s wild, how little we know.’

The pill’s effects are just as varied. ‘Targeted effects just aren’t possible when taking a hormone,’ writes Dr Hill. ‘The hormones in birth control are picked up by all the cells in the body that have sex hormone receptors. This means that they simultaneously influence the activities of billions of cells at once, echoing throughout the body from head to toe – particularly in the brain.’

This revelation doesn’t mean we should stop trusting doctors or drugs, however. It just means we owe it to ourselves to be curious, and remain alert for emotional changes, however ambiguous.

So before you start a new medication, consider keeping a journal. ‘The brain likes to play tricks on us when we are sad or anxious, and tells us that we have always felt that way. Having hard evidence of your mood prior can be a good way for you to think about your past more objectively,’ says Dr Hill.

‘In the future, we are going to be shocked that it took us so long to realise medication changes who we are,’ she continues. ‘One of the next frontiers in medicine is understanding the experiential effects of the medications we’re taking – and that includes the effect on our personality.’

The common medicines that could alter your mood

Heartburn pills

Among the most commonly used drugs in the world, proton pump inhibitors used to treat heartburn and acid reflux have been linked with a greater risk of developing depression, particularly among the elderly. They interfere with the absorption of vitamin B12, a nutrient that produces chemicals that affect our thinking.

Asthma and arthritis drugs

Corticosteroids such as prednisone can save lives – their powerful anti-inflammatory effect treats asthma, allergies and rheumatoid arthritis. But they can also cause depression, mania and ADHD, because they act on areas of the brain that regulate serotonin and dopamine – our ‘happy’ hormones.

Parkinson’s drugs

A 2010 study showed 17 per cent of people on dopamine agonists – used to treat shaking and other physical symptoms of Parkinson’s – experience ‘impulse control disorder’, from excessive shopping to uncontrollable sexual urges. In 2011 a married father of two sued the manufacturer of one of these drugs, saying it turned him into a gambling and gay sex addict, which led to him being raped and attempting suicide eight times. He won a six-figure payout.

Antibiotics

Overuse can make antibiotics less effective at treating infection – and a 2015 review of UK medical records linked repeat courses of antibiotics to increased anxiety and depression. It’s thought this may be down to their effect on bacteria in our guts, which interact with our brain chemistry.

How the Pill Changes Everything: Your Brain on Birth Control by Dr Sarah E Hill is published by Orion, price £14.99. Order a copy for £8.99 (a discount of 40%) until 5 July at whsmith.co.uk by entering code youchange at checkout. Book number: 9781409178835.