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My experience supplementing with NAC: benefits, side effects, potential risks

Article at a Glance
  • N-Acetylcysteine, or NAC, is a powerful antioxidant that is used by hospitals in cases of acetaminophen overdose.
  • NAC helps restore glutathione in the liver after an influx of toxicity has caused levels to drop.
  • NAC has been used extensively by psychiatrists looking for alternative therapies for various mood disorders and mental health issues.
  • NAC has demonstrated promise as a biofilm disrupter, both bacterial and fungal.
  • Certain genotypes may be sensitive to the sulfur containing amino acids in NAC.
  • NAC can be hard on the stomach.
Genes Mentioned
NAC benefits

Since the likelihood is that you’re skimming this article on your phone, about to head back to Instagram or a dating app, I am going to lead off with a fact about NAC that will, hopefully, grab your attention.

N-Acetylcysteine, or NAC for short, is one of a handful of dietary supplements that is also used quite frequently in hospital settings. That’s right, when a patient comes to the hospital with an acetaminophen overdose, standard of care is to use intravenous NAC to protect the liver and help the body excrete accumulated toxins.1


When we take acetaminophen, a metabolite called NAPQI is produced, which in high enough doses is very toxic to the liver.1 Under normal circumstances, one of the body’s most important “endogenous” antioxidants, glutathione, cleans up this mess before any lasting harm can be done. However, when mega doses are taken, hepatic glutathione stores (glutathione in the liver) run out and the body doesn’t have enough to detoxify the bad stuff the acetaminophen is producing. The result can be liver damage and, if enough is taken, death.

Enter NAC, which is a glutathione precursor and proven nutrient for restoring depleted glutathione levels. A double blind, placebo control study showed a 28% reduction in mortality when IV NAC was administered after an acetaminophen overdose.2

I list NAC as one of my supplements to take to avoid a hangover because drinking alcohol also draws down glutathione stores and taking NAC is one of the most effective ways to build the glutathione back up.

So, we’ve already learned two important things about NAC:

  1. It’s a glutathione precursor and can increase levels of glutathione in the liver after depletion (but not when glutathione levels are already normal, so it’s not going to “supercharge” your glutathione levels)
  2. It’s one of the supplements used in clinical settings (kind of like S. Boulardii with antibiotic associated diarrhea)

While I cycle NAC on and off, and most certainly don’t take it everyday for months at a time, it’s one of the supplements I “believe in,” which is a short list these days.

What are some of the other proven benefits of NAC?

NAC can improve mood

Science Grade:

For me, one of the pleasant surprises of supplementing with NAC is improved mood. Now, I don’t want to overstate things. Just as Dan Harris titled his meditation app “10% happier,” and not “holy crap, meditation has made me into a different person and I never ever have anxiety,” the impact of NAC on my mood has been subtle, but also real and tangible. I feel an enhanced sense of calm and focus and notice additional resiliency to work stress. During the past week, I’ve also found that NAC is in the class of supplements that gives me a social boost.  With 500mg of NAC in my system, I was a touch more outgoing and likely to engage with waiters, people around the city, and more upbeat in general. If I were to quantify, I’d say the difference is in the 10-15% range.

It seems my observations about NAC boosting mood have been demonstrated in clinical studies. Double blind, placebo controlled studies have shown promise for the ability of NAC to help alleviate depressive disorders. In fact, while not all the studies have shown efficacy, I was particularly impressed by this meta analysis of 5 studies which found NAC has value in treating depression.3 Keep in mind that the meta analysis started with 38 studies had to throw out 33 of them for failure to meet “inclusion criteria,” which I take as a message that many of the NAC studies out there are garbage.

NAC helps alleviate anxiety and mental health issues

Science Grade:

The likely mechanism here is NAC seems to work as a glutamate antagonist.4

For those of you who have regularly read the blog, you’ll remember glutamate is the “gas pedal” neurotransmitter, which is great, unless pressing on the gas has you accelerating through a brick wall. An excess of glutamate can lead to anxiety, as well as excitotoxicity, which some theorize is the cause of many neurodegenerative disorders.56 Another calming amino acid, L-theanine, is also a glutamate antagonist.

NAC is actually quite popular in the field of psychiatry and medical literature documents NAC experiments to treat everything from OCD, to addiction, to Bipolar disorder.4

NAC destroys biofilm

Science Grade:

In his book, Toxic, Dr. Neil Nathan, an M.D. in Northern California who has gained a reputation for taking on especially sensitive mold and Lyme patients, discusses the use of NAC as an agent for detoxing from gliotoxin, one of the waste byproducts of Candida and some mold species.

Why would NAC be used as part of an anti-fungal protocol?

There is evidence that NAC can disrupt and destroy bacterial and fungal biofilms, which are the “cocoons” fungal species build around themselves to protect their colonies from destruction. These biofilms become resistant even to antibiotics, which makes antioxidants and enzymes, like NAC, Lumbrokinase and Nattokinase, which can penetrate and destroy biofilm, all that much more important.7

NAC and the Lungs

Science Grade:

NAC is an anti-mucous agent, and many people take it for conditions like COPD, which involves the unpleasant build up of mucus in the lungs.8 The idea is that NAC can help alleviate an increase of oxidative stress and inflammation in the lungs, but it’s also important to be aware that there are studies on the other side of the divide as well. Just as eating animal protein rich in pro growth amino acids, like the BCAAs, can speed cell growth, both good and bad, there is emerging evidence that antioxidant supplements have the potential to protect both good and bad cells as well.

A study in mice found that NAC supplements could accelerate tumor growth in the lungs. The takeaway for the authors was that NAC could actually be dangerous in high risk populations, such as those struggling with COPD.9

NAC and Sulfur Sensitivity

Science Grade:

I’ve written before about the CBS family of genes and how certain SNPs in those pathways can affect sulfur metabolism. One SNP, CBS C699T, is associated with an up-regulation of sulfur metabolism, which can lead to higher levels of ammonia in the blood as well as gastrointestinal symptoms.

Side note, SNPs in the urea cycle can have the same result.

What does this have to do with NAC?

NAC, alpha lipoic acid, and glutathione are all “sulfur donor supplements,” meaning their building blocks are sulfur containing amino acids.10 In individuals whose bodies use up these amino acids too rapidly, as is the case when certain CBS variants are present, sulfur sensitivity can occur. As such, and with 28% of the population carrying at least one copy of the CBS C699T SNP, some people will have reactivity to NAC and the sulfur family of supplements.

NAC Side Effects – My Experience

I’m writing this review after taking a 500 mg dose of NAC every day for a week. As I’ve made clear in my recent post Are Your Supplements Making You Sick? I tend to cycle on and off virtually every supplement I take. It’s rare that I take any supplement for longer than a few weeks without some time off. Just the way I do it with supplements.

Previously, I’d taken NAC as a one off supplement a few hours before consuming alcohol, and experienced no side effects, but after a week of steady use, the main side effect I experienced was stomach upset and, unfortunately, diarrhea. On the 7th day of dosing at 500mg, I developed heart burn (in retrospect it may not have been wise to take NAC on a breakfast of just scrambled eggs) and eventually what some in the MCT oil world call “disaster pants.” The long and the short of it is that the acidity of NAC really upset my stomach after a somewhat prolonged period of usage. The fact that I developed stomach sensitivity after a week at a 500mg daily dose made me marvel at some of the psychiatric trials using doses 4 times this large.

I do plan to take NAC in the future, but when I do, I think I will either split the 500mg dose into two pills, and perhaps even cut it with an alkalizing agent like potassium citrate. Taking NAC with a proper full meal will also be a priority.

Finding the best NAC supplements

Omega Curcumin by Nordic Naturals

In my post on glutathione, I highlighted a product by Nordic Naturals, called Omega Curcumin, which I like because it uses high quality omega 3 fatty acids to encase a small dose of glutathione. Liposomal (fat encased) delivery mechanisms for glutathione have been shown to be far more bioavailable than traditional oral preparations, however, there is a rub. Most of these liposomes are made with omega 6 fats, many of them phospholipids that are prone to oxidation, can raise TMAO levels, and depending on the way your body absorbs plant sterols, can actually make their way into the blood stream and bind to pro-atherogenic lipoproteins, such as Lp(a), where they can do damage to the heart. The nice thing about the Omega Curcumin product is, in addition to a fairly bioavailable form of glutathione, it also contains a decent sized dose of NAC (200 mg if 2 soft gels are taken which is the recommended dose).

Thorne Research NAC

In light of the fact that, at least in my case, a 500mg dose caused side effects, and in light of the mouse research on tumor growth I cited above, why not consider a smaller dose of NAC? If you don’t find efficacy at that small of a dose, it’s always possible to move up to a product like this one from Thorne (a brand I trust) that contains 500mg of NAC.

I used the Thorne product in my experiment. The Thorne product is nice because you can take apart the capsule and stagger the 500mg dose across the span of a day, or as I have toyed with, combine a secondary agent that can neutralize some of the acidity of the NAC.

John O'Connor

John O'Connor is the founder of Gene Food. He is passionate about nutrition, genetics, and wellness and uses this blog to publish self experiments as well as some of the research that the Gene Food team does internally to highlight stories of bio-individuality.

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  1. Kitt says:

    I’ve was recently informed that I have a progressive lung disease, in the past (over 20 yrs) ago I was told I had COPD and I’m doing fine and I’m now a 73 yr old female, my Dr said that I would have to go on steroids, which I have many side effects in the past and do not want to go on steroids. I’m currently seeking alternative medicine and I’ve been interested in NAC…. I purchased them just today, but I hesitate taking them until I can find out more. It surprises me that all of the posts on all the ailments that are treated with NAC, it appears too good to be true, So, in conclusion I would appreciate comments.

  2. Edward says:

    Avoid fluoroquinilone anti-biotics if you can (they carry a FDA black box warning), including e.g. Ciprofloxacine. But fluoroquinilones are often an last resort anti-biotic. However, taking antioxidants (like NAC) alongside fluoroquinolones seems to mitigate their negative effects, according to Science magazine (March 2018).

  3. Ray says:

    NAC600 has worked great with me. Have used 1 am and pm for several yrs and has greatly reduced my COPD Exasperations to almost nil . I forgot to mention I have stage 4 COPD. My lung doc recommends for me also. Everyone is diff but works for me!

  4. Amber says:

    Everyone is different, i take it on a completely empty stomach, I read it works better that way, and Ive had no issues, I also take a much higher dose than 500mg.
    You didnt really mention any positive side effects for yourself other than the hangover issue.
    Makes me wonder if you could really benefit from just taking it for a week.
    It took weeks of it being in my system before I saw any positive results.

  5. Isabel says:

    Good Article, I have learned to take NAC not with a meal, only with a small bite of toast or something. Especially not with protein. Maybe that’s why your stomach was upset.

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