Supplement company NOW just completed another round of testing products on Amazon, with 25 different brand samples of the methylcolabamin form of vitamin B12 purchased in January 2025. Methyl B12 was chosen for its high cost and high potential to fail potency tests. Compared to other expensive supplements, B12 appeared to have fewer brands that failed to meet claimed potency.

NOW purchased two bottles of each product to test at its own internal labs and cross-reference the results with a reputable external laboratory. But they didn’t publish the results from an external lab this time due to “significant inconsistencies,” and “a lack of clarity in test methods.”

NOW noted that vitamin B12 can be difficult to test due to complexities inherent to different supplement matrices, and the fact that the compound is unstable. NOW reported that its results came from internal high-performance liquid chromatography (HPLC) tests following a validated method aligned with the USP monograph for methylcobalamin. “However, due to the inherent instability of vitamin B12 and the difficulty contract labs face in maintaining stable standards and accurate analyte recovery, results may vary across different testing environments,” NOW reported.

Key Findings

Both NOW products tested above the label claim, at 140% and 114%, due to intentional overages. Among the other 23 brands tested, 11 brands exceeded their label claim, with six testing over 120%. 12 brands tested below 100%, with three showing potency between 90% and 100% and three brands containing a 0% to 1% potency.

The brand Monohar showed 0% potency in this round, which was a repeat performance after its SAMe supplement also yielded a 0% in 2024 tests. The brand aSquared showed some improvement in quality compared to previous testing, but only achieved 56% potency compared to its label claim in its liquid product.

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%.

This is NOW’s 20th time testing Amazon products, and it shared its results with Amazon and FDA.