How Long Does It Take for NAC Supplements to Work? 

N-acetyl-cysteine (NAC) is a derivative of the amino acid L-cysteine.

Owing to its potent antioxidant and anti-inflammatory properties, NAC may help manage or treat certain conditions, support the body's immune response, and improve exercise performance.

However, if you have thought about supplementing with NAC for its purported benefits, you may wonder how long it takes to experience its effects.

This article explains everything you need to know about supplementing with NAC, including what effects you might expect and the factors that influence when you might experience them.

Understanding N-Acetyl-Cysteine (NAC)

NAC is a dietary supplement form of the amino acid L-cysteine, from which it's derived. It was originally introduced in 1967 as an over-the-counter medication to break down viscous mucus that can damage the lungs, pancreas, and other organs in patients with cystic fibrosis (1).

Since then, NAC has been clinically used as a drug to improve lung function in patients with chronic obstructive pulmonary disease (COPD) and protect the liver from acetaminophen overdose, among other clinical uses.

Although the Food and Drug Administration (FDA) prohibits ingredients from being sold as dietary supplements if they were first approved as a drug, the FDA has allowed the sale of NAC supplements to continue (likely due to NAC's exceptional safety profile).

By replenishing glutathione levels, NAC increases your body's ability to neutralize free radicals — unstable molecules that can damage your cells. Glutathione is a tripeptide made from the amino acids glycine, cysteine, and glutamic acid and supports numerous cellular processes, notably detoxification and antioxidant status. Often referred to as the "master" antioxidant, glutathione is an essential mediator of cellular defense mechanisms; depleted glutathione levels are implicated in aging and various disease states (2).

Some fruits and vegetables contain NAC, but only in small amounts.

Foods that naturally contain NAC include:

• asparagus

• cucumbers

• parsley

• tomatoes

• red and green peppers

• lemons

• grapefruits

• strawberries

However, because the body only absorbs 4–10% of the NAC consumed, you need much more than what you could realistically get from food to achieve therapeutic effects (1). And while many foods contain cysteine, supplementing with cysteine is impractical because it is unstable and susceptible to oxidation.

Similarly, glutathione is rapidly broken down in the body before it has a chance to be absorbed, limiting its bioavailability as a dietary supplement.

For these reasons, supplementing with NAC is a more efficient and cost-effective way to increase the body's pool of cysteine to replenish glutathione (3).

NAC supplements come in both capsule and powder forms and contain NAC alone or alongside other ingredients promoted to combat oxidative stress or support liver health, like quercetin, glycine, or milk thistle.

Benefits of NAC

Supplementing with NAC can be an effective way to support your body's level of glutathione and, in turn, your overall longevity, immune function, and more.

Here are some of the evidence-based health benefits of NAC supplementation:

Hepatoprotection (Liver Defense)

NAC replenishes the liver's glutathione stores by providing cysteine. It also acts as an antioxidant and binds to toxic compounds.

Through its antioxidant effects, some evidence also suggests that NAC can block fat from accumulating in the liver and consequently causing fatty liver disease (1).

Just like NAC can prevent or decrease acetaminophen-induced liver damage, it may also help protect the liver from other liver-toxic drugs (4).

Studies also suggest that NAC can improve liver function following damage caused by excessive alcohol use (5).

Anti-inflammatory Roles

Inflammation is a reaction by the immune system against injury and infection.

It can be either acute (short-lived) or chronic (long-lasting).

Chronic inflammation underlies many diseases, including diabetes, arthritis, respiratory conditions, heart disease, and kidney disease, among many others.

By combating various inflammatory proteins and pathways, NAC may be useful for reducing inflammation.

To this point, a review of 28 studies found that patients with various inflammatory conditions who supplemented with 500 to 2,000 mg for three weeks to one year experienced significant decreases in several inflammatory proteins and markers of oxidative stress (6).

Improved Physical Exercise Performance

NAC may increase oxygen delivery to cells and increase adenosine triphosphate (ATP) production, allowing you to exercise harder for longer.

In a review of 16 studies, supplementation with 1,200 mg of NAC decreased fatigue and increased muscle power during various exercise tests trained an physically active health men (7).

The men also demonstrated increases in antioxidant capacity and levels of cysteine and glutathione.

Most of the men supplemented with NAC once before or during the exercise test, but in other studies, the men supplemented with it daily for three to 21 days.

However, in a different study, NAC supplementation only improved exercise performance in men with low glutathione stores, suggesting that baseline glutathione status may play a role in determining whether supplementation is useful for increasing exercise performance (8).

In either case, while NAC may promote athletic performance in the short-term, like other antioxidant supplements, it might harm performance in the long-term by decreasing the body's ability to adapt to the stress induced by exercise.

Other Notable Health Benefits of NAC

Some research suggests that NAC supplementation may offer health benefits for treating various conditions, including (9):

• Inflammatory bowel disease. Supplementing with 800 mg daily of NAC reduced the number of patients with Crohn's disease or ulcerative colitis who experienced a relapse of their symptoms while tapering off a corticosteroid medication.

• Fertility. Dosages varying from 1,200 mg to 1,800 mg per day have been shown to improve fertility in women with polycystic ovary syndrome (PCOS) by decreasing insulin resistance, and enhancing fertility in men by supporting semen quality.

• Mental health conditions. Several studies — some of which have been conducted in animals — suggest that NAC supplementation may improve symptoms of various mental disorders, including schizophrenia, obsessive-compulsive disorder, depression, and bipolar disorder, in part by influencing certain neurotransmitters and reducing oxidative stress.

There are also some animal and in vitro studies to suggest that NAC may improve glycemic control and suppress the proliferation of certain types of cancer (1).

How Long Does it Take for NAC to Work?

Some studies suggest that NAC has immediate effects, primarily for improving exercise performance when taken before or during a workout or sporting event.

However, because NAC's primary role is to replenish and maintain glutathione stores by providing cysteine, the time it takes to experience benefits largely depends on your baseline glutathione stores.

With low baseline glutathione stores, you're likely to experience significant improvements in various aspects of health from NAC supplementation, such as immune system function, certain blood tests, as well as exercise performance.

There are various reasons why your body's glutathione level can become depleted, including:

• Poor diet. Diets rich in saturated fats, added sugars, and refined grains, like the Western or Standard American Diet, can promote inflammation and oxidative stress.

• Chronic disease. The inflammation and oxidative stress that underlie many chronic diseases can deplete glutathione stores.

• Stress. Stress can dysregulate immune function and increase inflammation.

• Age. Aging is associated with elevated oxidative stress, causing a decline in glutathione stores.

Depending on these factors and your baseline glutathione stores, it could take several weeks to replenish your stores.

In one study, it took men with low glutathione stores 30 days of supplementation with 2,400 mg of NAC to sufficiently replenish their levels (8).

Conversely, a different study found that just 21 days of daily supplementation with 200 mg of a NAC prescription drug was sufficient to demonstrate its antioxidant properties in patients at risk for metabolic syndrome (10).

The time it can take also depends on how efficiently your body can produce glutathione from NAC and its two other amino acids, which diminishes with age and in the presence of certain diseases.

In either case, although one trial suggested that 200 mg of NAC daily could effectively increase glutathione levels, most clinical trials suggest that at least 1,200 mg per day for 4-8 weeks is needed to experience its benefits.

Potential Side Effects of NAC

NAC is remarkably safe (11). In fact, protocols for using NAC to treat acetaminophen overdose call for around a 10-gram dose for a 150-pound person and up to about 90 grams over 72 hours (12).

Considering that most NAC supplements usually provide around 600 mg per serving, there's a very high margin of safety.

However, large doses, specifically in amounts administered clinically, can cause digestive symptoms, such as:

• nausea

• vomiting

• diarrhea

• excessive gas

• acid reflux

NAC may interfere with certain medications, specifically blood thinners and blood pressure medications, so it's best to talk with your doctor before supplementing NAC if you take these medications (1).

NAC has an unpleasant odor and taste — usually resembling rotten eggs due to the sulfur-containing residues of cysteine — but it shouldn't make you smell the same from consuming it.

FAQ – Frequently Asked Questions

How long does it take for NAC to work for anxiety?

Clinical studies that have evaluated NAC for mental disorders like anxiety have used dosages ranging between 600 and 3,600 mg daily for four to 24 weeks (12, 13).

Can I take NAC before bed?

When you take NAC does not appear to be important, unless you're using it to enhance exercise performance, so you can take it before bed or when it's convenient.

Can you take NAC with other supplements?

It's likely safe to combine NAC supplements with other supplements, but talk to your doctor first if you take prescription medications since NAC can interact with certain drugs.

How long after taking NAC can you eat?

Eating does not influence the absorption of NAC, so you can take your NAC supplement at any time.

How much NAC should I take?

Research suggests that at least 1,200 mg daily is necessary to experience NAC's benefits. However, depending on the reason for supplementing, smaller doses — between 600 and 800 mg daily — can also be effective.

What to expect when you start taking NAC?

Depending on the dose, duration, and reason, the effects you feel from supplementing with NAC may be obvious or nonexistent. While unproven, you could experience improved energy levels, sleep, and brain health, especially if you have low glutathione levels.

The Bottom Line on NAC

NAC is a supplemental form of cysteine. The body needs cysteine to produce and replenish glutathione, a powerful antioxidant. As such, supplemental NAC

NAC offers anti-inflammatory and antioxidant benefits independent of its role in replenishing glutathione stores. Supplementing with NAC confers liver-protective, anti-inflammatory, and ergogenic properties.

The time it takes to experience benefits from NAC depends on various factors, including the dosage and baseline glutathione levels, which can be influenced by your lifestyle and overall health. Most of the evidence suggests that the benefits of NAC become apparent within 3 to 4 weeks of daily supplementation.