Background

N-acetyl cysteine (NAC) comes from the amino acid L-cysteine. Amino acids are building blocks of proteins. NAC has many uses and is an FDA approved drug.

N-acetyl cysteine is an antioxidant that might play a role in preventing cancer. As a drug, it's used by healthcare providers to treat acetaminophen (Tylenol) poisoning. It works by binding the poisonous forms of acetaminophen that are formed in the liver.

People commonly use N-acetyl cysteine for cough and other lung conditions. It is also used for flu, dry eye, and many other conditions, but there is no good scientific evidence to support many of these uses. There is also no good evidence to support using N-acetyl cysteine for COVID-19.

Although many dietary supplement products contain N-acetyl cysteine, the US FDA has stated that it's illegal for dietary supplements to contain N-acetyl cysteine since it's technically an approved drug. But as of August 2022, the FDA is considering changing this stance. It may allow for N-acetyl cysteine in dietary supplements as long as no safety issues come up. A final decision is pending. Prescription N-acetyl cysteine products are available under the guidance of a healthcare provider.

Safety Safety definitions

When taken by mouth: N-acetyl cysteine is likely safe for most adults. N-acetyl cysteine is an FDA-approved prescription drug. It can cause side effects such as dry mouth, nausea, vomiting, and diarrhea. It has an unpleasant odor that some people find hard to tolerate.

When inhaled: N-acetyl cysteine is likely safe for most adults, when used as a prescription medication. It can cause swelling in the mouth, runny nose, drowsiness, clamminess, and chest tightness.

Special Precautions & Warnings:

Pregnancy: N-acetyl cysteine is possibly safe when taken by mouth or inhaled during pregnancy. N-acetyl cysteine crosses the placenta, but there is no evidence that it harms the unborn child. But N-acetyl cysteine should only be used when medically needed.

Breast-feeding: There isn't enough reliable information to know if N-acetyl cysteine is safe to use during breast-feeding. Stay on the safe side and avoid use.

Children: N-acetyl cysteine is likely safe when taken by mouth in doses of 900-2700 mg daily for up to 12 weeks.

Allergy: Don't use N-acetyl cysteine if you are allergic to acetyl cysteine.

Asthma: N-acetyl cysteine might cause bronchospasm in people with asthma if inhaled or taken by mouth. If you take N-acetyl cysteine and have asthma, you should be monitored by your healthcare provider.

Bleeding disorder. N-acetyl cysteine might slow blood clotting. N-acetyl cysteine might increase the risk of bruising and bleeding in people with bleeding disorders.

Surgery. N-acetyl cysteine might slow blood clotting. This might increase the risk of bleeding during and after surgery. Stop taking N-acetyl cysteine at least 2 weeks before a scheduled surgery.

Effectiveness

Dosing & administration

N-acetyl cysteine is an FDA approved prescription drug. It can be taken in various ways, including by mouth, by IV, and by inhalation. It is most commonly taken by mouth in doses of 600-1200 mg daily. Speak with a healthcare provider to find out what type of product and dose might be best for a specific condition.

N-acetyl cysteine is also available in many dietary supplements. But according to the FDA, using N-acetyl cysteine in supplements is illegal because it is an approved drug. Supplement products should not be used in place of prescription products.

Interactions with pharmaceuticals

Activated charcoal

Interaction Rating=Moderate Be cautious with this combination.

Activated charcoal is sometimes used to prevent poisoning in people who take too much acetaminophen (Tylenol) or other medications. Taking N-acetyl cysteine at the same time as activated charcoal might decrease how well it works for preventing poisoning.

Chloroquine (Aralen)

Interaction Rating=Moderate Be cautious with this combination.

Chloroquine is a drug used to treat malaria. N-acetyl cysteine might reduce the effects of chloroquine against malaria.

Medications for high blood pressure (Antihypertensive drugs)

Interaction Rating=Moderate Be cautious with this combination.

N-acetyl cysteine might lower blood pressure. Taking N-acetyl cysteine along with medications that lower blood pressure might cause blood pressure to go too low. Monitor your blood pressure closely.

Medications that slow blood clotting (Anticoagulant / Antiplatelet drugs)

Interaction Rating=Moderate Be cautious with this combination.

N-acetyl cysteine might slow blood clotting. Taking N-acetyl cysteine along with medications that also slow blood clotting might increase the risk of bruising and bleeding.

Nitroglycerin

Interaction Rating=Major Do not take this combination.

Nitroglycerin can dilate blood vessels and increase blood flow. Taking N-acetyl cysteine seems to increase the effects of nitroglycerin. This could increase the risk for side effects including headache, dizziness, and lightheadedness.

Interactions with herbs & supplements

Herbs and supplements that might lower blood pressure: N-acetyl cysteine might lower blood pressure. Taking it with other supplements that have the same effect might cause blood pressure to drop too much. Examples of supplements with this effect include andrographis, casein peptides, L-arginine, niacin, and stinging nettle.
Herbs and supplements that might slow blood clotting: N-acetyl cysteine might slow blood clotting and increase the risk of bleeding. Taking it with other supplements with similar effects might increase the risk of bleeding in some people. Examples of supplements with this effect include garlic, ginger, ginkgo, nattokinase, and Panax ginseng.

Interactions with foods

There are no known interactions with foods.