Glutathione vs. NAC: Which Is Better?

Glutathione has been gaining attention in the supplement world, and it’s not hard to see why. It’s one of the body’s most important antioxidants, helping protect cells against oxidative stress. It also plays roles in immune function and helps the body process potentially harmful compounds.1 Interest in maintaining glutathione levels has also grown alongside research into healthy aging, as some studies suggest that glutathione levels tend to decline as we get older.25

That has made glutathione supplements increasingly popular among people looking for everything from antioxidant and immune support to healthy aging and better-looking skin. But if you start investigating whether you should actually take one, there’s a good chance you’ll come across another supplement: N-acetylcysteine (NAC).

NAC isn’t glutathione, but the two are closely connected — closely enough that you may even see NAC recommended instead of glutathione itself. So, if your goal is to support your glutathione levels, which approach makes more sense?

In this guide, we’ll break down how glutathione and NAC are related, what the research tells us about supplementing with each, and how to decide which one may be a better fit for you.

Glutathione and NAC are closely related, but they support your body in different ways. Taking glutathione directly gives you the antioxidant itself, while NAC supplies cysteine, one of the amino acids your body uses to make its own glutathione. Both approaches have been shown to increase glutathione levels in human research.2 3

If you have to choose just one, we’d give NAC a slight edge. It has a longer clinical track record, helps your body make its own glutathione, and has demonstrated health benefits beyond its role in glutathione production.4 24 But taking glutathione directly isn’t far behind. Longer-term human research shows that oral supplementation can increase the body’s glutathione stores, though how well it works may depend partly on the dose and how the supplement is formulated.2 5

Taking both also makes sense in theory, since glutathione provides the antioxidant itself while NAC supplies cysteine, often the limiting building block in your body's own glutathione production.17 But research into taking the two supplements together is lacking, so the case for combining them remains theoretically strong rather than demonstrably strong.

We’ll take a closer look at using them together later in this guide. We also provide guides to the best NAC supplements and the best glutathione supplements on the market right now.

Over the past two decades, Innerbody Research has helped tens of millions of readers make more informed decisions about their health and wellness.

Our team has extensively researched both glutathione and NAC, including how they work in the body, their relationship to one another, and the evidence behind their potential health benefits. Across our research on these supplements, we’ve reviewed more than 150 scholarly sources covering glutathione, NAC, antioxidant support, healthy aging, respiratory health, and other areas of ongoing research.

Additionally, like all health-related content on this website, this guide was reviewed by one or more members of our Medical Review Board for accuracy. We’ll continue to monitor emerging research on glutathione and NAC and update this guide as new evidence becomes available.

Glutathione and NAC are closely connected, but they aren’t the same thing. To understand why they’re so often compared, it helps to start with what each one does.

What is glutathione?

Glutathione is an antioxidant your body makes naturally from three amino acids: cysteine, glutamate, and glycine.6 It’s found throughout the body, where one of its most important jobs is helping protect your cells from oxidative stress — damage that can occur when unstable molecules called free radicals build up faster than your body can neutralize them.

Glutathione does more than fight oxidative stress, though. It also plays roles in immune function and helps your body process and remove certain potentially harmful compounds.6 And as we noted earlier, research suggests that glutathione levels tend to decline with age, which has helped fuel interest in maintaining them as we get older.1

In other words, glutathione is an important part of your body’s built-in antioxidant defense system.

What is NAC?

N-Acetylcysteine, better known as NAC, is a form of the amino acid cysteine. NAC has several actions of its own, but one of the main reasons it comes up alongside glutathione is that your body can use NAC as a source of cysteine to make glutathione.7

The basic relationship is fairly straightforward: NAC provides cysteine, and your body can combine cysteine with glutamate and glycine to make glutathione.6 7

This is why NAC and glutathione supplements are so often compared. Taking glutathione gives your body the antioxidant itself, while taking NAC provides one of the building blocks your body can use to make its own.

Which approach does a better job of increasing glutathione is a separate question — and one we’ll look at next.

If your main goal is increasing your body’s glutathione levels, both NAC and glutathione supplements can work, but neither is a clear winner. The reason comes down partly to how differently they get there.

Taking glutathione directly

Taking glutathione sounds like the simplest approach: if you want more glutathione, why not just take more of it? The problem is that glutathione is made from three amino acids, and enzymes in your digestive tract can break it apart before much of the intact antioxidant reaches your bloodstream.5

That may help explain why human studies haven’t always agreed. In one four-week trial, 1,000mg of oral glutathione per day didn’t significantly increase glutathione levels in healthy adults.8 But a larger six-month trial found that both 250mg and 1,000mg daily increased glutathione stores, with the larger increases generally occurring at the higher dose.2

In other words, oral glutathione can work, but dose and duration may affect how much benefit you get from it. How the supplement is formulated may matter, too, since certain delivery methods are designed to help protect glutathione during digestion.

Using NAC to make more glutathione

NAC takes an indirect approach. Your body breaks down and processes NAC extensively after you swallow it, so only a relatively small portion reaches the bloodstream as unchanged NAC.9 But that doesn’t mean the rest is wasted. As your body processes NAC, it can make more cysteine available, and cysteine is one of the three amino acids your cells use to make glutathione.7 In other words, NAC doesn’t need to remain intact for your body to use it to support glutathione production.

Human research supports this pathway. After oral NAC supplementation, researchers have found higher cysteine and glutathione levels even when NAC itself was no longer detectable.24

There’s a catch, though. Giving your body more cysteine doesn’t guarantee that it will make more glutathione. How much NAC helps may depend partly on how much glutathione your body needs and whether cysteine is actually in short supply.3 7

That may help explain why NAC doesn’t increase glutathione in every study. In one trial of 114 healthy older adults, a combination of NAC and glycine didn’t significantly increase glutathione across the group as a whole. A follow-up analysis suggested that participants with lower glutathione production and higher oxidative stress may have responded better, although that wasn’t the study’s primary analysis.10

So, neither route is quite as straightforward as it might seem:

• Glutathione takes the direct route: You’re taking the antioxidant itself, but some can be broken down during digestion before your body can use it.
• NAC takes the indirect route: You’re giving your body a building block for glutathione, but your body still has to turn that raw material into the finished antioxidant.

What do head-to-head studies show?

Unfortunately, we don’t have much research directly comparing the two approaches.

One small crossover study gave 20 people with metabolic syndrome NAC, conventional oral glutathione, and sublingual glutathione — a form designed to dissolve under the tongue rather than simply being swallowed. After three weeks with each supplement, sublingual glutathione performed better on several measures of glutathione status than either conventional oral glutathione or NAC.11

Those results give glutathione an interesting point in its favor, but the study is far too small and narrow to settle the question. It included only 20 people, lasted three weeks per treatment, and specifically enrolled people with metabolic syndrome. For now, we’d call it a draw. Both approaches can increase glutathione, but neither has been shown convincingly to work better across the board.

And increasing glutathione is only one way to compare these supplements. NAC and glutathione have also been studied for different health effects, which may matter more depending on why you’re considering either one.

Whether NAC or glutathione makes more sense depends partly on why you’re taking it. The two overlap when it comes to antioxidant support because NAC supplies cysteine that your body can use to make glutathione. But NAC also has effects that aren’t dependent on glutathione, while taking glutathione directly may be more relevant for certain goals of its own.6 7

Human research reflects those differences. In some areas, one supplement has a clearer rationale or stronger evidence than the other; in others, neither has enough research to call a clear winner.

Yes. There’s a reasonable biological case for taking NAC and glutathione together, since the two enter the glutathione system in different ways. Glutathione supplements provide the antioxidant directly, while NAC supplies cysteine your cells can use to make additional glutathione.6 7

That means taking both isn't necessarily redundant. Your cells are constantly using, recycling, and making glutathione, and the amount available at any given time depends partly on the raw materials needed to produce more of it.17 In theory, taking glutathione while also supplying cysteine through NAC could support this system from two different directions.

What we don't have is strong human evidence showing that the combination works better than either supplement alone. Most clinical research has studied NAC and glutathione separately, and the small head-to-head study we discussed earlier compared the two rather than combining them.11

So, while the mechanism behind taking both makes sense, we'd view the combination as biologically plausible rather than proven to be more effective.

Both glutathione and NAC appear to be well-tolerated at the doses commonly used in supplements. Glutathione has been studied at doses up to 1,000mg daily for six months, while a review of NAC safety found that oral doses ranging from 600mg to 3,000mg daily were generally well tolerated in clinical studies.2 19

Side effects are still possible with either supplement, though they’re generally mild.

• Glutathione may cause gastrointestinal discomfort and other minor adverse effects.2
• NAC may cause nausea, diarrhea, heartburn, gas, headache, and other digestive complaints.4 19

There are also some situations where we’d recommend additional caution:

One area where the safety picture gets more complicated is cancer. Both NAC and glutathione affect the body’s antioxidant defenses, and antioxidants aren’t necessarily helpful or harmful in every cancer context. Cancer cells experience oxidative stress just like healthy cells do, and glutathione can help them manage it. That can become a problem because oxidative stress can damage or kill cancer cells, so strengthening their antioxidant defenses could potentially help them survive. In some cancers, higher glutathione activity has also been associated with tumor progression and resistance to certain treatments.18

But there’s another side to the story. Oxidative stress doesn’t selectively damage cancer cells — it can harm healthy cells, too. Some cancer treatments generate oxidative stress as part of how they work, but that same process can contribute to treatment-related side effects. Glutathione has therefore been investigated for its potential to protect healthy tissue and reduce some of these effects.18 NAC can also influence cellular processes beyond glutathione production, including oxidative stress, inflammation, and cell signaling.4 This makes its potential role in cancer similarly complicated.

For healthy adults, current human evidence doesn’t show that taking NAC or glutathione causes cancer. The bigger uncertainty is what either supplement might do when cancer is already present or during cancer treatment. If you have active cancer or are receiving cancer treatment, we’d recommend discussing either supplement with your oncology team rather than taking it on your own.

Choosing a glutathione or NAC supplement

So, which one should you actually take? For most people choosing between the two, we lean toward NAC. Rather than giving you glutathione directly, NAC supplies cysteine that your body can use to make its own. It also has a longer clinical track record and has been studied for benefits beyond its role in glutathione production.4 7 And from a practical standpoint, it’s relatively straightforward to shop for.

That doesn’t mean taking glutathione directly is a lesser option. Human research shows that oral glutathione supplementation can increase the body’s glutathione stores, and taking the antioxidant itself may make particular sense for certain goals, such as skin pigmentation.2 15 The main drawback is that some of the glutathione you swallow can be broken down during digestion, so formulation may matter more than it does with NAC.5

Here are a couple of things to consider when shopping:

If you choose glutathione, there’s a reasonable argument for both liposomal and standard supplements. Liposomal glutathione packages the antioxidant inside tiny fat-based structures called liposomes, which are intended to help protect it as it moves through the digestive tract. That could help address one of the potential limitations of taking glutathione orally, since some of it can be broken down during digestion.5 Early human research on liposomal glutathione has also been encouraging, with one small study finding increases in glutathione stores after supplementation.26

Standard oral glutathione, by comparison, doesn’t use this liposomal delivery system. It may not offer the same potential protection during digestion, but it has a longer track record in human research, including studies showing that daily supplementation can increase the body’s glutathione stores.2 So, if your priority is sticking closely to the type of glutathione used in much of the successful clinical research, there’s a good argument for choosing a standard capsule.

We currently lean toward liposomal glutathione for most people, which is one reason our top pick is Codeage Liposomal Glutathione. It provides 500mg of Setria glutathione per two-capsule serving — the same daily dose used in one small study of liposomal glutathione.26 Still, Codeage won’t be the best fit for everyone. Our full guide to the best glutathione supplements compares it with lower-cost options and other formulations, including our picks for liver support and liquid glutathione.

If you choose NAC, shopping is a little simpler. Because you’re taking a source of cysteine rather than glutathione itself, you don’t need to seek out the same kinds of specialized delivery systems. Life Extension, our best overall pick in our guide to the best NAC supplements, provides 600mg per capsule, making it easy to get 600mg or 1,200mg.

There is one decidedly less appealing thing about NAC: its smell. NAC naturally has a sulfurous odor that’s sometimes compared to rotten eggs. That doesn’t mean the supplement has gone bad, but if the smell is enough to put you off taking it regularly, glutathione may be the more practical choice. Our full NAC guide also covers lower-cost options, powders, and products geared toward more specific goals.