What does the NIH label data show about Cystine?

Cystine appears as an ingredient in 74 dietary supplement product labels cataloged in the NIH Dietary Supplement Label Database (DSLD). The NIH classifies Cystine within the Amino acid category. That frequency reflects how often manufacturers list Cystine on submitted labels, both in single-ingredient products focused on this nutrient and in broader multi-ingredient formulas such as multivitamins, specialty blends, and category-spanning formulations. Across this catalog of 74 filings, the ingredient appears in products ranging from standalone capsules to combination formulas containing dozens of other components. Counting how many labels declare an ingredient is a useful way to gauge how common it is in the United States supplement market, though it does not indicate efficacy or safety on its own.

When reviewing products that contain Cystine, pay attention to a few label signals. First, the ingredient's amount per serving and any Daily Value (DV) percentage, some nutrients have an FDA reference daily intake (so a DV is shown), while others (many botanicals, amino acids, specialty compounds) do not. Second, the chemical form listed matters: the same common name can refer to several compounds with different absorption or bioavailability profiles, so the exact wording on the label is worth checking. Third, look at what else the product contains, a supplement listing Cystine alongside many other active ingredients may deliver a smaller amount than a single-ingredient product of the same total size. All of these data points are declared by the manufacturer on the label as filed with the NIH DSLD.

A reminder on scope: the DSLD is a label database, not an approval list. Dietary supplements are regulated in the United States under the Dietary Supplement Health and Education Act (DSHEA) of 1994, which does not require FDA pre-market approval for safety or efficacy. Inclusion of Cystine on a product label does not imply that the FDA has evaluated claims about the ingredient, verified its potency, or tested the specific bottle you may buy. Some ingredients have well-established research bases, others are far more speculative, and effects can vary by form, dose, and individual health status. This page presents factual label-frequency data and is not medical or nutritional advice, consult a licensed healthcare provider before starting, stopping, or combining supplements, especially if you are pregnant, take prescription medication, or have a medical condition.