Why some people with ME/CFS react more strongly to medications

R

Roym

Established Member
I’ve often noticed that people with ME/CFS seem to be unusually sensitive to certain medications, even at very low doses. Some describe stronger side effects, slower response, or feeling “wiped out” by medicines that most people tolerate well.
I’m not talking about allergy reactions, but more about things like increased fatigue, dizziness, brain fog, nausea, or just feeling unwell after taking a standard dose. I’ve also seen many members mention “I can only tolerate a quarter dose”, which is quite interesting.

There are a few possible reasons this might happen:

1. Slower metabolism or clearance
Some people may process medications more slowly. That means the drug stays in the body longer, which can make the effects feel stronger, even if the dose is small. This isn’t dangerous in itself, but it can make side effects more noticeable.

2. Nervous system hypersensitivity
ME/CFS is known to affect how sensitive the nervous system can become. If the brain and nerves are already in a sensitive state, even mild medication effects can feel amplified.

3. Immune system involvement
Some medications interact, directly or indirectly, with the immune system. Since immune dysregulation is often discussed in ME/CFS, it might explain why certain medicines feel particularly strong or unpredictable.

4. The body is already in a “low energy” or “high stress” state
When the body is struggling just to maintain basic balance, introducing a new chemical (even a mild one) might feel like “too much energy demand” or stress.
This isn’t medical advice, just general observations. I’m interested in hearing how others here experience medication sensitivity:
• Do you feel you react more strongly to medicine than most people?
• Does it happen with all types of medication or only certain ones?
• Have you noticed a difference between tablets, liquids, patches, or other forms?

I’d love to better understand how common this is and how people here describe their experiences.
 
Roym said:
Some describe stronger side effects, slower response, or feeling “wiped out” by medicines that most people tolerate well.
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I’m not convinced there’s anything to this, and here’s why:
  • I don’t see any reason to count the effects you listed as evidence of the same problem because they are very different from each other. What kind of issue would cause all of them?
  • Some people in the general population claim to be generally sensitive to drugs, and there’s no data showing that this is more common in pwME
  • Different drugs interact with the body in so many different ways that I can’t figure out how someone could have a general sensitivity to all/most of those very different processes like some people claim
Roym said:
Do you feel you react more strongly to medicine than most people?
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No, I don’t, but I’ve been perceived that way in the past, which is part of why I’m skeptical of this. I think my psych NP thinks I’m sensitive when I’ve actually just had some normal drug side effects. I think people may be too quick to attribute normal reactions (and in the case of ME, normal fluctuations in symptoms) to some kind of unusual sensitivity.

Of course, I could be totally wrong. Curious to see what others think.
 
Verity said:
No, I don’t, but I’ve been perceived that way in the past, which is part of why I’m skeptical of this. I think my psych NP thinks I’m sensitive when I’ve actually just had some normal drug side effects. I think people may be too quick to attribute normal reactions (and in the case of ME, normal fluctuations in symptoms) to some kind of unusual sensitivity.

Of course, I could be totally wrong. Curious to see what others think.
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I think similarly.

Since we can't attribute improvements to drugs without careful studies, in my head something similar often applies to supplements or medications for largely the same reasons, unless we're talking about already well known side effects. From the placebo-controlled trials we've seen with very heavy drugs at standard dosages I don't recall patients with ME/CFS reporting unusual effects disproportionally for the active substance.

And I don't see it being too ME/CFS specific either. I've heard stories from all sorts of people, healthy or with illnesses reporting all sorts of things about things they have consumed without them saying the same thing a year later. In a space where there's little good observations, there's more room for ones with less credibility to flourish. And anyways should one not expect different medications to have very different reasons, if they existed?
 
Verity said:
This is a really good point.
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I think this would be heavily selection biased no?
Those who are likely to sign up for heavy drug trials probably overlap very little with those who are very sensitive to meds.

I don’t think we can assume drug trial participants to be representative of pwME at large in this case.
 
Yann04 said:
I think this would be heavily selection biased no?
Those who are likely to sign up for heavy drug trials probably overlap very little with those who are very sensitive to meds.

I don’t think we can assume drug trial participants to be representative of pwME at large in this case.
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And this is also a good point. :)
 
Less of an issue these days ( ironically as my daughter is worse than a couple of years ago)
Whilst drugs do have reactions- fillers can be problematic - Synthetic vit E is one.
Some colours can be problematic
 
I react badly to a lot of meds, usually things listed on the list of side effects, but bad enough to make me discontinue them.

It's so long since I was well I can't really remember whether I reacted badly to meds, and in any case had little need of them apart from ordinary things most people need sometimes.
 
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