N-Acetyl-L-Cysteine powder is an organic substance, white crystalline powder, similar to garlic smell, sour taste. It is hygroscopic, soluble in water or ethanol, insoluble in ether and chloroform. It is acidic in aqueous solution and contains thiols, which can break the disulfide bond ( − S − S − ) of the mucoprotein peptide bond, so that the mucoprotein chain becomes a small molecular peptide chain and reduces the viscosity of mucoprotein.
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Chemical Formula |
C5H9NO3S |
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Exact Mass |
163 |
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Molecular Weight |
163 |
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m/z |
163 (100.0%), 164 (5.4%), 165 (4.5%) |
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Elemental Analysis |
C, 36.80; H, 5.56; N, 8.58; O, 29.41; S, 19.65 |
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Morphological |
liquid |
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Color |
soluble in water |
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Melting point |
106 – 108 °C ( lit. ) |
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Boiling point |
407.7 ± 40.0 ° C ( predicted ) |
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Density |
1.22 g / ml at 25 ° C (lit.) |
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Storage conditions |
2-8 ° C |
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specific rotation |
− 35.1 oC ( c = 2, H2O ) |
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Acidity coefficient ( pKa ) |
9.52 ( 30 °C ) |
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Flash point |
133 ° f |
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Solubility H2O |
100 mg / mL with heating |
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Vapor density |
1.03 (vs air) |
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Refractive index |
24 ° ( C = JPC Method ) |
N-Acetyl-L-Cysteine powder (NAC), as a sulfur-containing amino acid derivative, has been developed as a expectorant since the 1960s. Its application areas have expanded from respiratory disease treatment to sports nutrition, neuroprotection, and beauty and skincare. Its core value lies in the thiol group (- SH) in its molecular structure, which not only endows NAC with strong antioxidant capacity, but also makes it a key precursor for glutathione (GSH) synthesis.
In the field of beauty and skincare, NAC has become a core component in anti-aging and skin health management by clearing free radicals, inhibiting inflammation, promoting collagen synthesis, and regulating melanin metabolism through multiple mechanisms. Here is its detailed description:
The antioxidant effect of NAC originates from the thiol group (- SH) in its molecule, which can directly react with reactive oxygen species (ROS) such as hydroxyl radicals (· OH) and hydrogen peroxide (H ₂ O ₂) to generate stable thiol derivatives, thereby interrupting the chain reaction of free radicals. For example, in vitro experiments, NAC can significantly reduce the ROS levels of keratinocytes induced by ultraviolet (UV) radiation, protecting the cell membrane from lipid peroxidation damage.
NAC inhibits the nuclear factor kappa B (NF - κ B) signaling pathway, reduces the release of pro-inflammatory factors such as TNF - α and IL-6, and alleviates the damage of chronic inflammation to the skin. For example, in acne models, NAC can reduce sebaceous gland activity and decrease the number of inflammatory papules. In addition, NAC regulates Th1/Th2 balance, inhibits allergen induced contact dermatitis, and provides protection for sensitive muscles.
The biological basis of NAC: from antioxidant to cell protection
NAC promotes the proliferation of keratinocytes and fibroblasts by activating the extracellular signal regulated kinase (ERK) pathway, accelerating skin barrier repair. In the photoaging model, NAC can increase skin thickness by 15% -20% and reduce wrinkle depth. Its mechanism includes: inhibition of matrix metalloproteinases (MMPs): NAC reduces collagen degradation by decreasing the expression of MMP-1 and MMP-9. Promoting collagen synthesis: NAC upregulates the expression of type I collagen by activating the TGF - β/Smad pathway. Protecting mitochondrial function: NAC clears mitochondrial ROS, maintains ATP synthesis, and delays cellular aging.
Reducing wrinkles and improving skin firmness, NAC inhibits MMP-1 activity and reduces collagen degradation. For example, in vitro experiments showed that 10mM N-Acetyl-L-Cysteine powder can increase collagen synthesis in fibroblasts by 25%. NAC enhances the activity of lysyl oxidase (LOX), promotes elastin fiber cross-linking, and improves skin elasticity.
The clinical study showed that after 12 weeks of continuous use of the cream containing 5% NAC, the depth of wrinkles around the eyes of the subjects decreased by 18%, and the skin firmness increased by 22%. Uniform skin tone and whitening: NAC reduces melanin synthesis by inhibiting tyrosinase activity. For example, in melanoma cell experiments, 5mM NAC can reduce melanin content by 30%. NAC reduces skin dullness by clearing lipid peroxides.
The clinical study showed that the use of essence containing 3% NAC for 8 consecutive weeks increased the skin color brightness of the subjects by 15% and reduced the stain area by 20%.NAC activates the PPAR - α pathway, enhances the synthesis of ceramides and free fatty acids, and strengthens the skin barrier. For example, in the atopic dermatitis model, NAC can reduce transcutaneous water loss (TEWL) by 25%. NAC alleviates burning and stinging sensations by inhibiting TRPV1 receptor activity. The clinical study showed that the use of cream containing 2% NAC for four consecutive weeks reduced the erythema area of sensitive muscle subjects by 30%.
Emergency Antidote for Acetaminophen Overdose Poisoning
The most central and important clinical use of NAC powder is as an antidote for acetaminophen (paracetamol) poisoning. Excessive acetaminophen can deplete hepatic glutathione and produce highly toxic metabolites that damage liver cells.
As a precursor of glutathione, NAC can rapidly replenish intracellular antioxidants in the liver and block the destruction of liver tissue by toxic intermediates. Clinically, it is often prepared into an oral or intravenous solution. Administration within 8 hours after poisoning yields the best efficacy, significantly reducing the risk of acute liver failure and death. It is recognized worldwide as a first-line antidote.
Respiratory Diseases: Mucolysis and Improved Sputum Clearance
NAC can break the disulfide bonds of mucin in sputum, reduce sputum viscosity, and make it easier to cough up. Therefore, it is widely used in diseases accompanied by thick purulent sputum, such as chronic obstructive pulmonary disease, bronchitis, pneumonia, and bronchiectasis.
The powder formulation can be prepared into a nebulized solution or oral solution to reduce airway obstruction, improve ventilation, and is especially suitable for adjuvant therapy in elderly patients, those with postoperative expectoration difficulties, and during the recovery period of respiratory infections. It is a commonly used clinical mucolytic agent.
Antioxidation and Liver Protection
As a potent antioxidant, NAC can scavenge free radicals and alleviate oxidative stress. It is used for the adjuvant treatment of alcoholic liver injury, drug-induced liver injury, and non-alcoholic fatty liver disease. It can increase glutathione levels in the body, stabilize cell membranes, reduce inflammatory responses, and protect liver cells from lipid peroxidation damage. In the field of health products, NAC powder is also often used as a functional ingredient for liver protection, anti-fatigue, and metabolic improvement.
Adjunctive Improvement of Respiratory Tract Infections and Pulmonary Inflammation
In respiratory diseases such as influenza and COVID-19, NAC can alleviate pulmonary inflammatory responses, reduce airway hyperresponsiveness and the risk of cytokine storm through its antioxidant and anti-inflammatory effects. Although not a specific antiviral drug, it can be used as adjuvant therapy to relieve symptoms such as cough, excessive sputum, and chest tightness, improving patient comfort and recovery speed.
Other Clinical and Healthcare Applications
NAC can also be used for the adjuvant intervention of polycystic ovary syndrome, depression, obsessive-compulsive disorder and other diseases, as it can regulate neurotransmitters and improve oxidative stress status. In addition, in the laboratory field, NAC powder is often used for cell culture protection to prevent oxidative damage to cells, and as a sulfhydryl-protective agent in biochemical experiments. Its application scenarios cover medicine, scientific research, health products and many other fields.
I. Core Synthetic Process
The mainstream manufacturing process of N-Acetyl-L-Cysteine powder uses L-Cysteine Hydrochloride Monohydrate as the starting material, synthesized via the key step of acetylation reaction. First, the raw material is added to a ceramic reaction kettle and dissolved in water, followed by the introduction of acetic anhydride. The pH is adjusted to 12 with 20% caustic lye solution; the system is then sealed, heated to 125–135°C under a pressure of 0.4 MPa, and maintained for 2 hours to complete acetylation. Subsequently, hydrochloric acid is added to adjust the pH to 3, and the solution is transferred to a cooling kettle, where brine cooling is applied to below 3°C to precipitate crystals. Solid-liquid separation is performed using a centrifuge to obtain the crude product. This process is mature and stable, features high raw material conversion rate, and is suitable for large-scale industrial production.
II. Refining and Drying Process
The crude product requires multiple refining steps to improve purity. The crude product is dissolved in purified water, decolorized with 5% activated carbon, and recrystallized at low temperature after filtration to remove unreacted raw materials and by-products. The crystals are washed with ice ethanol and diethyl ether to further eliminate impurities. Vacuum low-temperature drying is adopted, with drying at 75–85°C for 12 hours, and the loss on drying is strictly controlled to ≤1.0%. After drying, the product undergoes jet milling and sieving to ensure uniform particle size. Meanwhile, ambient humidity is maintained at ≤40% RH to prevent powder caking.
III. Quality Control Standards
The entire production process complies with GMP and ISO standards, implementing strict quality control. Purity requirements: HPLC detection ≥99.0%, single impurity ≤0.1%. Physicochemical indicators: pH 1.5–2.5, specific rotation +21.0° ~ +27.0°, residue on ignition ≤0.1%, heavy metals ≤10 ppm. Microbial limits: total aerobic microbial count ≤1000 CFU/g, absence of Escherichia coli. Each batch is assayed by iodometric method or HPLC to ensure the content is within 98.0%–102.0%, meeting pharmacopoeial standards.
IV. Packaging, Storage and Transportation Specifications
The finished product is packaged in double polyethylene bags plus aluminum foil bags under vacuum, with an outer 25 kg fiber drum to block oxygen and moisture. Storage and transportation require protection from light, sealed conditions, temperature ≤25°C and humidity ≤60% RH to avoid oxidative degradation. A complete batch traceability system is established throughout the process, with full records from raw materials to finished products, ensuring stable product quality and safe use.
The chemical synthesis of N-Acetyl-L-Cysteine powder can be traced back to the late 1950s, originating from researchers' efforts to improve the stability and biological activity of L-cysteine. As a sulfhydryl-containing amino acid, L-cysteine is prone to oxidative inactivation and is difficult to use directly in medicine.
Between 1950 and 1960, German and Italian scientists conducted N-terminal acetylation modification on L-cysteine via the acetic anhydride acylation method, successfully synthesizing stable NAC powder and determining its molecular formula as C₅H₉NO₃S. It was confirmed that acetylation protects the sulfhydryl group and improves water solubility and in vivo stability. In 1961, its chemical structure was fully confirmed by X-ray diffraction and infrared spectroscopy, laying the foundation for subsequent medical applications.
In 1963, NAC was first launched in Italy as a mucolytic agent under the trade name Mucomyst. Studies found that its sulfhydryl group can break the disulfide bonds in sputum mucin, reduce sputum viscosity, and significantly relieve expectoration difficulties in patients with chronic bronchitis and asthma. It was approved by the U.S. FDA as a prescription drug in 1966 and included in the European Pharmacopoeia in the late 1960s, becoming the world's first oral/nebulized mucolytic agent and launching large-scale clinical use. In the early 1970s, the NAC powder formulation became the mainstream preparation due to its good stability and ease of compounding.
III. Major Breakthrough: Antidote for Acetaminophen Poisoning (1970s)
The period from 1974 to 1977 marked a turning point in the history of NAC. American scholar Rumack and his laboratory team discovered that acetaminophen overdose depletes hepatic glutathione and causes hepatic necrosis. In 1975, Piperno and Berssenbruegge confirmed through animal experiments that NAC can efficiently replenish glutathione and neutralize toxic metabolites, with a detoxification effect far superior to cysteine and methionine. In 1977, a British team led by Prescott published clinical research establishing NAC as the first-line antidote for acetaminophen poisoning. In 1985, the FDA formally approved it for this emergency indication, elevating NAC from a mucolytic agent to a core emergency drug.
In the 1990s, NAC was included in the WHO Model List of Essential Medicines, and its powder formulation was widely used in nutritional supplements, adjuvant liver disease treatment, and antioxidant therapy. Since the 21st century, its antioxidant, anti-inflammatory, and immunomodulatory effects have been verified, leading to applications in adjuvant treatment for chronic obstructive pulmonary disease, pulmonary fibrosis, HIV infection, and supportive intervention for COVID-19. From chemical synthesis to a life-saving emergency drug, NAC has become a classic cross-disciplinary, multi-field pharmaceutical agent thanks to its unique mechanism, and still plays a pivotal role in clinical and healthcare settings today.
FAQ
What is N acetyl L cysteine powder used for?
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N-Acetylcysteine (NAC) is a drug approved by the Food and Drug Administration (FDA) and recognized by the World Health Organization (WHO) as an essential drug, widely used for the treatment of acetaminophen overdose (paracetamol) and more recently as a mucolytic agent, in respiratory diseases.
Can I take n-acetyl-L-cysteine every day?
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You may take NAC daily for a short time, but research about the safety of taking NAC every day for the long term is limited. A 2021 literature review found that most studies use it with specific therapeutic goals between 6 weeks and 6 months. Toxicity from NAC intake is rare, particularly in low doses.
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