N-acetyl-L-cysteine is a stable, bioavailable form of the amino acid L-cysteine.* It occurs naturally in Allium plant species, especially onions. In the body, NAC serves as the precursor your cells use to produce glutathione.

When taken as a supplement, NAC may help support several physiological functions, including:

• Glutathione production and the body's natural antioxidant defenses*
• Exercise performance during strenuous training*
• Recovery between training sessions*
• Respiratory and immune health*

Glutathione is a tripeptide built from three amino acids: glycine, glutamine, and cysteine, and it is the body's primary intracellular antioxidant. It is the molecule your body relies on to help neutralize the normal cellular stress that vigorous muscle contraction creates.* Of its three building blocks, cysteine is the rate-limiting one, which means the body's capacity to produce glutathione is constrained by how much cysteine is available.*

Supplemental glutathione taken orally faces an absorption challenge, because the intact tripeptide is subject to breakdown in the digestive tract before it reaches the cells where it works. NAC is a small, stable cysteine derivative that is absorbed efficiently and may be more bioavailable than supplemental glutathione.* If you already use a glutathione product, NAC isn't a replacement, it supplies the precursor your body needs to produce its own.*

It is a practitioner-aligned serving delivered in a single capsule, and it is the highest serving currently available among NSF Certified for Sport® NAC products.¹ The same 900 mg per capsule appears in the Designs for Health NAC formula used in clinical practice; NAC 900 brings that serving into a formula that is NSF Certified for Sport® and screened for banned substances.

Take 1 capsule per day, at any time of day. There is no timing window to manage and no need to work it around training sessions.

Yes. NAC 900 is NSF Certified for Sport® and checked for banned substances, making it preferable for competitive athletes subject to testing.

Reactive oxygen species generated during exercise are part of how the body adapts to training. NAC works differently: it supplies the rate-limiting precursor your body uses to produce its own glutathione, supporting the antioxidant system already in place rather than adding antioxidants directly.* Discuss your specific protocol with your health-care practitioner.

Yes. NAC 900 is designed to fit into a daily performance nutrition routine alongside other Designs for Sport® products. One capsule daily, at any time of day, with no timing conflicts to manage.

Consult your health-care practitioner before use, particularly if you are pregnant or nursing, taking anticoagulant medication, or have a known sensitivity to sulfur-containing compounds. As with any supplement, individual history and current medications should be reviewed with a qualified practitioner.

NSF Certified for Sport® is an independent certification program that tests sports supplements for quality, label accuracy, contaminants, and more than 280 substances banned by major athletic organizations. Pro-Formance Peptides™ carries this certification, giving athletes added confidence that the product meets strict safety and quality standards.