Question: Why does medicine have side effects

Ciarán O'Brien answered on 7 Nov 2014:

Lots of reasons, depending on the medicine.

Sometimes it’s because the medicine you’re taking is seen by your body as a foreign object, and your immune system tries to fight it off a bit. Vaccines actually depend on this, as a doctor gives you a harmless version of some more dangerous disease so that your body learns how to fight off the real thing. You’ll usually feel a little woozy or even develop a slight temperature, but that’s waaaaay better than dying!

Sometimes it’s because the medicine is designed to alter your brain chemistry, like anti-depressants do, and brain chemistry is so complicated that the medicines we design just aren’t able to do what we want them to do without accidentally setting off some other reaction. As our knowledge of brain chemistry improves, and we develop better ways of manufacturing these drugs, they’ll be able to reduce the side effects.

Antibiotics are used to kill off bacterial infections, but they can take a lot of innocent bacteria with them. Most antibiotics you see are pills you swallow, and they aren’t very picky which bacteria they kill, so while they kill off the bad bacteria making you ill, they’ll also kill off many others that were just living in your gut and even helping your body stay healthy, and the antibiotics will make you feel nauseous and give you diarrhea.

Sometimes it’s because the problem is a tumour, which is so similar to your own body (it’s just part of your body that grew out of control) that the chemicals we use to kill it off can’t help but damage the rest of you.

But not every medicine has side effects, and they can differ from person to person. If you’re worried about medicine having side effects, see if you can chat to your doctor about them. Sometimes they might have a different kind of medicine that does the same job but doesn’t cause you side effects.