Bloomingdale, IL—NOW has shared the latest results of its industry quality testing program investigating unfamiliar brands sold on online in an effort to raise awareness on low-quality products in the marketplace. This is NOW's 20th round of testing since the program began in 2017.

NOW noted the inherent complexity of testing Vitamin B-12 across different matrices and dosage forms and the analyte’s instability. For these reasons, NOW maintains, even reputable third-party labs may not be able to produce consistent test results. The company added: "NOW recommends that this material therefore become a priority for collaboration by testing proficiency expert groups."

About NOW's Methyl B-12 testing

This ingredient was selected for study due to its high cost and the potential failure of its potency label claim. NOW looked at 25 different brand samples of Methyl B-12 purchased on Amazon in January 2025. Two bottles of each brand of Methyl B-12 supplement (plus two NOW products) were purchased and subject to internal testing in NOW’s labs. Those results were cross-referenced with the results from a reputable external laboratory. However, NOW said  there were "significant inconsistencies from the external lab indicating a lack of clarity in test methods." Therefore, NOW chose not to publish those results.

Testing Methodology

All samples were analyzed using High-Performance Liquid Chromatography (HPLC) at NOW’s laboratories, following a validated method aligned with the USP monograph for Methylcobalamin. Due to the inherent instability of Vitamin B-12 and the difficulty contract labs face in maintaining stable standards and accurate analyte recovery, results may vary across different testing environments, NOW acknowledged.

Understanding Methylcobalamin

NOW explained: Methylcobalamin is a highly bioavailable form of Vitamin B-12. Other common forms include Cyanocobalamin and Adenosylcobalamin (Dibencozide). Since Vitamin B-12 is nearly absent in plant-based foods, it is often supplemented by vegetarians. Methylcobalamin is preferred for solid dose supplements due to its stability and immediate usability by the body, while Cyanocobalamin is more stable in liquid forms but requires conversion to an active form within the body.

NOW's observations from its  internal analysis:

NOW Products Performance:

Both NOW products tested well above the label claim at 140% and 114%. The company said this is due to intentional overages to ensure full potency at best by date. 

Market Performance:

Among the remaining 23 brands, 11 brands exceeded their label claim, with six testing over 120%. Twelve brands tested below 100%, with three showing potency between 90-100% and three brands containing only 0-1% potency.

Challenges with Dosage Forms:

Liquid and gummy forms were less stable and harder to analyze accurately compared to tablets and capsules. Only one product met potency regulations, while others ranged from 1% to 105%.

A table showing the results is available here.

NOW concluded that testing Vitamin B-12 is inherently challenging due to the instability of Methylcobalamin and the difficulty in obtaining consistent results across various matrices and dosage forms. "Contract laboratories often struggle with maintaining standard stability and accurate analyte recovery, contributing to the variability observed in this study," the company said. "Our internal data highlight the industry's need for more robust testing methods and quality control measures."