Fibromyalgia N-Acetyl Cysteine (NAC) Benefits and Side Effects


New Member
My doctor suggested N-Acetyl Cysteine (Life Extension, 1200 mg twice a day) for fibromyalgia. I started at 600 mg twice a day almost a week ago. My stomach has been very upset about 80% of the time since then--a sensation in the upper abdomen like hunger pangs but worse. I take the supplement with food and have started taking it with Pepto Bismol as well, but it still hurts. I can't rule out the possibility of a minor stomach virus or something unrelated to the NAC; I've had this type of abdominal pain before but never for more than a few hours and never so intensely.

I get side effects from pretty much everything, and my doctor seems to be annoyed with me and just tells me to stop taking the problematic medicine/supplement right away without thinking about ways to deal with the side effects.

I'm not feeling any benefits from the NAC yet and I've read that many people have pain relief from the dose I'm currently taking. Not sure whether it's worthwhile to stick with it (and increase the dose) at this point but I don't want to give up too quickly. Has anyone had the same side effect, or any benefits, and at what dose?


Well-Known Member
You could try reducing the dose to one that doesn't give you side effects and then slowly increase it if you feel you need to.

700mg a day gave me nose bleeds (it can thin the blood) so I reduced to a quarter that and now it's fine. It has helped my fatigue in that it seems to be helping me pull out of a particularly bad patch.

The fact they are tablets/capsules might also be an issue. I take mine as a powder dissolved in water. I have to warm the water for a few seconds in the microwave as it won't dissolve in cold water. It tastes a bit like soluble asprin (not too bad).

I have tiny measuring spoons that I found on amazon to help me measure dose (1/8, 1/16 and 1/32 tsp). 1/4 tsp is about 700mg.

You can take acetyl-l-carnitine in the same way, although that tastes really horrible and might be better taken in juice.

I found the powders on Amazon and they are much cheaper than tablets/capsules. The brand I've used for both is "Bulk Powders" - I don't know how international that is, but it's available in the UK.
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Well-Known Member
My Doctor recommended that too.
He say it might take a while to have it's anti-inflamatory effects. But I took twice and my stomach was upset.
I think it's the fructose in the powder... I'm trying to find some non flavoured product... Does anyone know about it?

Who Me?

Well-Known Member
I think NAC is one of those things that may work behind the scenes. So you may not feel any better. I don't have FM so I'm not sure of the pain but I think many people take it at the dose you said. It helps make glutathione.

I take 1200/mgs per day.

Like others suggested you can take one a day and see how that goes. I always start much lower than they recommend and build up. I bought some blank caps on eBay so I have stuff around in case I want to split something further.

@Strike me lucky takes this and might be able to add more since my brain is mush today.


New Member
Thanks for your suggestions, everyone.

I knew NAC was a blood thinner, and was worried about that aspect of it—I can see why it might cause nose bleeds. I noticed that my nose and eyes became irritated, and I’ve had that effect, as well as abdominal pain, with other medicines/supplements that thin the blood.

I’m taking the Life Extension capsules because my doctor said that’s the only kind that was studied extensively enough to know it’s worth trying. But maybe powder in another brand would be worthwhile since I’m having such a hard time with the capsules. The stomach pain got so bad that I stopped them entirely 24 hours ago but still don’t’ feel back to normal. Maybe I’ll give it a week to feel better and then try a powdered version.

Tandrsc, the information on the small measuring spoons for powders is helpful—I’ll check that out on Amazon.


New Member
One more note on NAC: When my doctor suggested it, I thought he intended it to have a protective antioxidant effect--the sort of thing that might help with long-term health but not short-term pain relief. That seems to be what a few people in this thread are saying, and that's what a lot of the online literature says.

But he also mentioned that it has been shown to reduce chronic pain by reducing the excitatory neurotransmitter glutamate and helping with sensory gating. That's the reason I thought it might actually reduce pain but so far, research aside, I don't know anyone who has had that experience.

Health Rising has some information on this at "NAC’s effectiveness in ameliorating a sensory gating deficit may therefore lie in its role as a glutamate antagonist instead of (or indeed as well as) its antioxidant properties and role as a glutathione precursor."


Well-Known Member
NAC is the supplement that I would say gave me most benefit (with fatigue, not pain) but I started with a powder (tastes dreadful, I put it in orange juice or a fizzy vitamin C drink) and a small dose. No stomach problems for me so could be a coincidence.

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