Take a medicine and start feeling a bit off, and it's easy to assume you're imagining it. Sometimes you're not.
Author
- Dipa Kamdar
Senior Lecturer in Pharmacy Practice, Kingston University
It could be a known side-effect - the sort of thing listed on the leaflet in the packaging. Or it could be something known as an adverse drug reaction , or ADR.
The terms get used interchangeably, but they're not quite the same thing. An ADR is an effect that's new, unexpected, or more severe than anyone anticipated - and it can strike when you start a medicine, when your dose changes, or even after you've stopped taking it.
ADRs can happen for many reasons . We all process medicines differently. Your age, your genes and your underlying health can all shape how your body reacts.
Sometimes the dose is simply too strong for you. Or it could be caused by a clash between two medicines, or a medicine and food, or a medicine and a supplement.
And very occasionally, the culprit is the medicine itself: a defective or fake product containing the wrong ingredients, or none at all.
Healthcare professionals sort ADRs into several categories , but two matter most.
Type A reactions are the most common. They happen when a medicine's normal effects simply become too strong - blood thinners like warfarin causing bleeding, for instance, or painkillers like morphine and codeine causing drowsiness or slowed breathing.
These are usually predictable and tied to the dose. The same category covers side-effects that come from how a drug works in the body but aren't part of its actual job - the dry mouth caused by tricyclic antidepressants , for example.
Type B reactions are rarer and much harder to anticipate. Allergic reactions fall into this category - rashes, swelling, breathing trouble - such as those sometimes triggered by penicillin antibiotics .
These can happen even when you've taken the medicine exactly as prescribed.
There are other types of ADR too, and some take much longer to show up. Type C reactions build slowly, sometimes over months or years. Long-term steroid use thinning the bones is one example.
Type D reactions can appear long after you've stopped taking a medicine. Some cancer treatments, for instance, can cause heart problems that only emerge years later .
Type E reactions happen when you stop a medicine and your body reacts to its absence. These are withdrawal effects , and they're linked to antidepressants, sleeping tablets and epilepsy medicines.
The symptoms themselves can range from mild to serious. Headaches, nausea and rashes sit at one end. Severe allergic reactions, breathing difficulties, fainting and sudden changes in mood or behaviour sit at the other. If something feels unusual, severe, or turns up soon after starting a new medicine, it's worth taking seriously.
Don't just ignore it. If the symptoms are mild, check the patient information leaflet first to see whether it's already a known reaction.
Many common side-effects fade after a few days - diarrhoea with metformin is a good example. But if symptoms persist, get worse, or worry you, talk to a pharmacist or doctor.
They can tell you whether to keep taking the medicine, adjust the dose, or try something else. And if you experience symptoms such as difficulty breathing, a swollen face or throat, chest pain, a rapidly spreading rash , or severe dizziness, get emergency help straight away.
It's worth keeping a simple record too. Note down when symptoms started, what medicines you're taking, and anything that's recently changed - it all helps a doctor or pharmacist work out what's going on.
Where to report them
In the UK, anyone can report a suspected ADR through the Yellow Card scheme , run by the Medicines and Healthcare products Regulatory Agency (MHRA). You don't need to be a healthcare professional, and you don't even need to be certain the medicine caused it.
You can report reactions to prescription medicines, vaccines, herbal products and homeopathic remedies. You can also flag defective or fake medicines.
Reporting matters more than you might think. ADRs are a major cause of hospital admissions, especially for older people juggling several medicines at once, which piles extra pressure on the NHS.
Up to 16.5% of hospital admissions are linked to ADRs, according to one study . Another review , drawing on data from more than 1.5 million people in primary care, found that around 8% had experienced an ADR. Researchers believe that almost a quarter of those could have been prevented.
Heart medicines were the biggest culprits, especially treatments for high blood pressure, heart rhythm problems and blood thinners.
There are simple ways to cut your own risk. Read the patient information leaflet, ask your pharmacist about possible interactions, and keep an up-to-date list of everything you take, including supplements. Don't share your medicine with other people. And if something feels wrong, report it.
Medicines keep us well, but they're not risk free. Knowing what to watch for and what to do about it protects you and everyone else too.
Dipa Kamdar does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.
