Adverse Reaction? Side Effect? Are these the same?!

What is the difference between a side effect to medication, and an adverse reaction to medication? This is my story, and example, of an adverse reaction, to raise awareness

Natanya Mandel

9/26/20227 min read

a bottle of medicine pills and pills on a purple background
a bottle of medicine pills and pills on a purple background

As a migraine “long-hauler”, that is, someone who has had migraine forever (I was diagnosed 45 years ago, as a small child) … I have been through a lot with this disorder/disease/illness. Whatever you wish to call it. I think of it as an illness, because it impacts me every day.

Much as that is to live with, that isn’t what this piece is about. This piece is about when things go wrong with prescribed medication.

I’m going to tell my story of what happened to me recently. It’s my own experience of my own reaction. Not everyone will have these reactions, should they be unlucky enough to experience an adverse reaction.

I’m telling this story because I have noticed that there is quite a bit of confusion sometimes between side effects and adverse reactions. So, I thought a personal, lived experience may help. It certainly helped me understand the difference (I’d rather stay confused)!!

What is an adverse reaction, anyway?

It’s important to begin by explaining the difference between a side effect and an adverse reaction, as, in truth, these are quite different. A side effect can be very unpleasant (although, it may not be), while an adverse reaction is very unpleasant, quite to very severe as well as dangerous for your health. A side effect is quite predictable, an adverse reaction, not predictable at all.

A few examples of a side effect are: drowsiness, cough, weight gain or loss.

A few examples of an adverse drug reaction are: severe skin rashes, muscle breakdown, kidney damage, nerve injury, anemia.

In short, and as you can see, an adverse reaction is not predictable and can be quite dangerous.

My story

Back to my experience … I have taken many medications over the years, both as preventatives (every day medications, to reduce how often I get migraine attacks), and acute (what I take to try to stop an attack once it has begun). Like many with migraine disorder, I’m on a lifelong search to find what works. Mostly, these medications either don’t work, work for a while then stop working, or maybe have unpleasant side effects so I don’t tolerate them well.

My neurologist - who I think the world of - prescribed a new medication which was is in the SNRI class of medications, used to treat depression, social anxiety and panic attacks - as well as some other pain conditions, like migraine. The actual medication is irrelevant, as it is very helpful for many, many people. The point of telling my story is more to show the difference between side effects and adverse reactions, and also, to raise awareness of what an adverse reaction may look like, so that you don’t hesitate in contacting your health care practitioner (like I did).

So, with all that said, here is my sad and strange little tale (which to be honest, I find quite amusing).

Almost immediately upon taking this medication, my eye became irritated and slightly swollen. My appetite completely disappeared. I did not associate these things to the medication for a few days, until I forgot to take the medication one night (I was still on the starting dose), and the irritation subsided, the swelling went down. I took the medication again the next day, as prescribed, the irritation returned, the swelling also.

“Hmmm” I thought, “odd”.

I called the nurse at my neurologist's office. She asked me to stop taking the medication, sent me to my ophthalmologist to make sure everything was okay. My ophthalmologist cleared me of an adverse reaction (which in this case would have been glaucoma, I guess), so back on this medication I went. It is very, very good that I didn’t have glaucoma. That would have been A Very Bad Thing.

However, this time, the medication was quite the ride!

Again, my eye became irritated and slightly swollen, almost immediately and: I lost my appetite.

But then, as I continued to take this medication, on the lowest dose, new and strange things started to happen.

The first thing that happened, besides feeling a general malaise and unwellness (I assumed due to not eating), was, one day, I noticed 3 bites on the inner side of each knee. The same spot, both legs. Three small bites. Or what I thought were bites. Odd that they were on the same spot on both knees, as I was wearing long pants that day. However, it was early summer, I was outdoors, so, okay, I fobbed it off as insect bites. Unlikely, to be honest, as I’m also prone to skin rashes and allergic to quite a few things.

Anyway, I was losing weight. AWESOME!

Over the next few days and weeks, these bites did not go away. In fact, they spread, one leg worse than the other, and became an angry bruised looking rash. “Hmm…”. I thought, “odd”.

I still wasn’t eating. And the feeling of being unwell became worse. And worse. Also, I could not get up out of bed. I slept or rested about 70% of the time; and by 70% of the time I mean the time one is supposed to be up and about, enjoying the daylight hours (hopefully without a migraine attack).

I was happy, though. Happy might be overstating it, maybe positive would be a good description, I was very happy about losing weight. I was losing lots of weight despite being in bed most of the time.


As I became less and less well, and the rash on my legs became worse, and more itchy and annoying, I started becoming a little concerned. I did look up “adverse reaction” on google. I tend to use medical sites, but ….


The reaction wasn’t that bad, was it? I could handle it. I wasn’t getting too many migraine attacks (why would I? I was asleep most of the time). Actually, I’m not sure if I was getting attacks, I don’t recall.

Then, one day, my hand started hurting. It was the interosseous muscle (between the thumb and index finger). Don’t assume I knew what this muscle was - I had to use google to find out what it was called for this blog. Anyway, it really hurt.

I had difficulty using this part of my hand (annoying!). Opening the car door, writing things down, typing on the laptop. Using a fork. Everything required lots of breaks. I found myself massaging and rubbing this muscle all the time, particularly if I was using my hand.

After a few days, my arm and shoulder started hurting. REALLY HURTING. And It was hard to move my left arm properly. I did not lose full movement, but certainly did not have full movement. I could not move my arm properly.

That’s okay. It’s fine.

I’m losing weight. IT’S AWESOME!

I was beginning to realise that my thought process was not as it normally is. Why was I so attached to losing weight? I’m overweight, sure. But not overly, and honestly, I’ve never cared about this before. This is not something that I’ve ever particularly worried about.

Anyway, I kept taking it. Luckily, I did not go up to the full dose, I just kept myself on a fairly low dose this entire time.

I was feeling very unwell. It was hard to function, and I was sleeping much of the time. I still was not eating very much. My rash hurt and was itchy, my hand hurt, my arm and shoulder hurt, and it was becoming more difficult to move.

Then, one day, I could no longer move my thumb. At. All. It was completely immobilized. And - as used to pain as I am, the pain was a lot, even for me.

One of my good friends gave me a call. I hadn’t spoken to her in a while, and she said to me “Nat, you sound like shit”. This friend has very severe migraine disorder, and has been on many medications. She knows a lot.

So I told her what was going on … “... but I’m losing so much weight!” Haha, she laughed. I mean, it is funny. So crazy. I had become like a crazy person, clinging to this one useless thing.

She drew the line in the sand for me. And to be frank, I cannot thank her enough. I don’t know what would have happened if I continued along that path. I’m positive my husband tried very hard to draw this line in the sand. But, I think I needed to hear it from more than one person. I just was not thinking clearly at all.

She talked me down from taking the medication, talked me into calling my neurologist, reducing my dose, starting immediately - even without the neurologist's suggestion. I could always go back up again if the neurologist didn’t think it was the right thing to do. But it takes time to come off medication, you should rarely go cold turkey (unless you have to). In fact, my neurologist was willing for me to go cold turkey if I really needed to, which is an indication of how serious the reaction was.

All I can say is: Thank you to my friend. I’m so grateful to her. I’m grateful to my husband and children for putting up with this new version of crazy I discovered. They are so patient.

As you can see, the adverse drug reaction is quite different to a side effect from a medication. When I’ve had side effects before, sure they are sometimes unpleasant; many times a reason not to take it, but they were unlike anything like this. Additionally, side effects are expected - they occur for many people, so your health care team is able to warn you. An adverse reaction to medication is uncommon and unexpected, and takes unpleasantness to an entirely new level.

It’s been quite some time since coming off that medication. The adverse reaction sparked a severe vestibular and chronic migraine attack that lasted months, most annoyingly, over the warmer months of the Canadian year - my favourite time.

It has been very unpleasant. However, I am relieved that I am not on this medication anymore, and that this period is over.


I lost so much weight. It was awesome!!


hands reaching for each other at golden hour
hands reaching for each other at golden hour