Cysteine is an amino acid your body uses to create collagen, the major type of protein in connective tissue. Besides building your hair, skin and nails, cysteine helps convert glucose to energy and is a component of glutathione, a powerful antioxidant. Cysteine is classified as “conditionally essential,” meaning your cells can create it if other amino acids are plentiful. If your amino acid pool is deficient, you can increase your cysteine intake through the supplement N-acetyl cysteine (NAC).

NAC exists as an oral supplement that can be taken in capsule form and as a liquid that can be inhaled to prevent asthma attacks or infused intravenously to prevent liver damage caused by acetaminophen (Tylenol) overdose. The topical form can treat rashes and other skin problems. NAC has also shown promise in reducing the size of breast cancer tumors,1 and research shows that it can lower blood pressure and blood sugar.2 

But this versatile nutrient with a myriad of uses is getting harder to obtain and may soon be available by prescription only. In July 2020, the FDA sent warning letters to seven companies that marketed NAC as a hangover cure. The FDA often sends warnings to supplement manufacturers who make unsubstantiated claims regarding the health benefits of their products. But in this case, the FDA not only objected to the claim but to the ingredient itself, stating that NAC could not lawfully be marketed as a supplement because it had first been studied as a drug. The FDA warned that the NAC hangover products are not dietary supplements but unapproved new drugs that have not been evaluated and determined to be safe and effective.3

In December 2020, the Council for Responsible Nutrition, a trade association representing ingredient suppliers and manufacturers in the dietary supplement industry, urged the FDA to change its position, arguing that the inhaled drug first studied in 1963 was distinctly different from an oral supplement. Further, all oral NAC drugs marketed prior to 2016 had been withdrawn, leaving over-the-counter NAC the only option for decades.4 The FDA normally allows both prescription and non-prescription nutrients to coexist. One example is niacin, which is available over-the-counter in the vitamin section of grocery stores, and Niaspan, which is prescription-strength extended-release niacin.

In May 2021, retail giant Amazon began removing NAC from its website,5 bringing the issue to the public’s attention. As of this writing, NAC products are still available on Amazon. Supplement distributor Fullscript has some NAC-containing products available for direct-to-consumer purchase, while some are available only with a doctor’s recommendation. 

The FDA has not changed its position since last year, yet does not appear to be enforcing an outright ban while considering resolution of NAC’s status. If you use this supplement, as many have for COVID prevention due to NAC’s history as a respiratory treatment, make sure to stock up while you still can. You can also increase cysteine in your diet by consuming more high-protein foods such as chicken, turkey, eggs, sunflower seeds and legumes. If NAC becomes a prescription-only ingredient, you will still be able to obtain capsules by requesting them from your doctor.

Dr. Needle is a licensed naturopathic doctor with Optimal Health Center in Palm Desert and can be reached at (760) 568.2598 or visit


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