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?
 
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.
 
I am not aware of ever having had a problem with any medications. Though I have always tried to avoid taking any medications if I can. This reluctance to take prescribed medicine, may reflect a family prejudice possibly dating back to pre free health care days, when any medical involvement only took place if absolutely necessary.

Earlier in my ME I did have a number of years when I reacted badly to flue vaccine, so once I stopped working I stopped having the vaccine. However with the advent of Covid I started having flue vaccines again and no longer react badly, though I don’t know if this reflected changes in me or in the vaccines.

I wonder if there is any relationship between sensitivity to medicines and the other hypersensitivities we see in ME/CFS. My food sensitivities have increased over the course of my ME, though they are not related to the severity of my ME at any specific point in time. In contrast my sensory hypersensitivities do very much relate to how severe my current ME is. I have an apparent hierarchy in that sound hypersensitivity is an ongoing issue whereas requiring low light levels is only significant when I am more impacted by my ME, with sensitivity to smells only kicking in when I am at my very worst.

Are the different ‘sensitivities’ part of a single aspect of our disease process or very different mechanisms only overlapping in the language we use to describe them:
  • Alcohol sensitivity
  • Various food sensitivities
  • Chemical sensitivities
  • Drug reactions
  • Smell
  • Sound
  • Light
  • Touch
[edited to add temperature and possibly orthostatic intolerance to the list. Some ‘sensitivities’ seem to vary with current ME severity and others though seemingly triggered by having ME do not seem impacted by being in PEM or the concurrent severity of the condition. Some for me kick in immediately, as with the sensory issues, though they also contribute to triggering PEM, whereas others such as my food sensitivities seem to have their own time delays.]
 
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AliceLily said:
This was a very real problem for me in my severest years. It was significant and something I will never forget.
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Very big problem for me in particular alcohol and antihistamines. I have thought about this a lot and cannot make much sense of it scientifically but I do think there is something there to be worked out. Not sure if a subset of patients is more prone or just a disease severity thing. I know others on this forum who clearly have severe me/cfs do not react so badly to antihistamines.
 
Holinger said:
Very big problem for me in particular alcohol and antihistamines. I have thought about this a lot and cannot make much sense of it scientifically but I do think there is something there to be worked out. Not sure if a subset of patients is more prone or just a disease severity thing. I know others on this forum who clearly have severe me/cfs do not react so badly to antihistamines.
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I've just spent the last hour trying to write another post and what a mess that all was. I will write more another day when more rested but for now it felt like the ME chemical processes were very antagonistic in my severer years, so meds were creating further impact and not helping but hindering. I did tolerate antibiotic's though thankfully.
 
Holinger said:
Very big problem for me in particular alcohol and antihistamines. I have thought about this a lot and cannot make much sense of it scientifically but I do think there is something there to be worked out. Not sure if a subset of patients is more prone or just a disease severity thing. I know others on this forum who clearly have severe me/cfs do not react so badly to antihistamines.
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What sort of negative reactions did you have, and did you react to anything other than alcohol and antihistamines?
 
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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Possibly, but I’d also expect that all sorts of people sign up for trials in the hope of getting better regardless of any past experiences. Some trials probably also underreport certain (side) effects and it seems to me it would in many cases be impossible to distinguish something like feeling worse caused by a substance from something like PEM or natural fluctuations as part of any trial.

But in general I would think the selection bias runs in a different way: People that respond to a post on “side effects on medications” are often those that have experienced them or those with strong beliefs that such a thing cannot exist and similarly one will typically be more likely to find reports of something if it makes things better or worse but less if it does nothing. Personally, I’ve seen those things mentioned to be badly tolerated by some to be exactly those things that others claim as effective treatment.

Utsikt said:
I think one special consideration for pwME/CFS is that normal side effects might cause or contribute to PEM. So titrating things carefully might still be reasonable.
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And not only PEM. Simply feeling worse can be awful when you already feel horrible. Why should anybody want to endure that when in most situations the medications probably aren’t of much use?
 
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